Animals Planet

Therufous hornbill(Buceros hydrocorax), also known as thePhilippine hornbilland locally askalaw(pronounced KAH-lau), is a large species ofhornbillendemic to thePhilippines(the largest hornbill in the country). The are referred by locals as the "clock-of-the-mountains" due to its large booming call which typically occur of every hour. It occurs inmoist tropical lowland forest. They are now considered to be a threatened species and its reasons for decline beinghabitat destruction.huntingandpoachingfor theillegal pet trade.

Thegoatordomestic goat(Capra hircus) is adomesticatedspecies ofgoat-antelopetypically kept aslivestock. It wasdomesticatedfrom thewild goat(C. aegagrus) ofSouthwest AsiaandEastern Europe. The goat is a member of the animal familyBovidaeand the tribeCaprini, meaning it is closely related to thesheep. There are over 300 distinctbreedsof goat.[1]It is one of the oldest domesticated species of animal, according to archaeological evidence that its earliest domestication occurred in Iran at 10,000 calibrated calendar years ago. Domestic goat Temporal range:0.01–0Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓ Neolithic–Recent Apygmy goaton atree stump Conservation status Domesticated Scientific classificationKingdom:AnimaliaPhylum:ChordataClass:MammaliaOrder:ArtiodactylaFamily:BovidaeSubfamily:CaprinaeTribe:CapriniGenus:CapraSpecies: C.hircus Binomial nameCapra hircus Linnaeus,1758 Synonyms Capra aegagrus hircusLinnaeus,1758 Capra depressaLinnaeus,1758 Capra mambricaLinnaeus,1758 Capra reversaLinnaeus,1758 Goat-herding is an ancient tradition that is still important in places such as Egypt. Goats have been used formilk,meat,fur, andskinsacross much of the world.[3]Milk from goats is often turned intogoat cheese. Female goats are referred to asdoesornannies,intactmales are calledbucksorbillies, and juvenile goats of both sexes are calledkids.Castratedmales are calledwethers. While the wordshircineandcaprineboth refer to anything having a goat-like quality,hircineis used most often to emphasize the distinct smell of domestic goats. In 2011, there were more than 924 million goats living in the world, according to theUNFood and Agriculture Organization.

Theemu(Dromaius novaehollandiae) is the second-tallest living bird after itsratiterelative theostrich. It isendemictoAustraliawhere it is the largest native bird and the onlyextantmember of thegenusDromaius. The emu's range covers most of mainland Australia, but theTasmanian,Kangaroo IslandandKing Islandsubspecies became extinct after theEuropean settlement of Australiain 1788. Emu Temporal range:Middle Miocene – present PreꞒ Ꞓ O S D C P T J K Pg N Miocene–present  Conservation status  Least Concern(IUCN 3.1) Scientific classificationKingdom:AnimaliaPhylum:ChordataClass:AvesInfraclass:PalaeognathaeOrder:CasuariiformesFamily:CasuariidaeGenus:DromaiusSpecies: D.novaehollandiae Binomial nameDromaius novaehollandiae (Latham, 1790) Subspecies D. n. novaehollandiae(Latham, 1790) D. n. woodwardi(Mathews, 1912) (disputed) †D. n. baudinianusParker, S.A., 1984 †D. n. diemenensisLe Souef, 1907 †D. n. minorSpencer, 1906 Distribution in redSynonyms Casuarius novaehollandiaeLatham, 1790 Dromiceius novaehollandiae(Latham, 1790) Casuarius australisShaw, 1792 Dromaius aterVieillot, 1817 Dromiceius emuStephens, 1826 Casuarius diemenianusJennings, 1827 Dromiceius majorBrookes, 1830 Dromaeus irroratusBartlett, 1859 Dromaeus ater(Blyth, 1862) call of a female emu at theZOOM Erlebniswelt GelsenkircheninGermany Emus are soft-feathered, brown,flightless birdswith long necks and legs, and can reach up to 1.9 metres (6.2ft) in height. Emus can travel great distances, and when necessary can sprint at 48km/h (30mph); they forage for a variety of plants and insects, but have been known to go for weeks without eating. They drink infrequently, but take in copious amounts of water when the opportunity arises. Breeding takes place in May and June, and fighting among females for a mate is common. Females can mate several times and lay several clutches of eggs in one season. The male does the incubation; during this process he hardly eats or drinks and loses a significant amount of weight. The eggs hatch after around eight weeks, and the young are nurtured by their fathers. They reach full size after around six months, but can remain as a family unit until the next breeding season. The emu is an importantcultural icon of Australia, appearing on thecoat of armsand various coins. The bird features prominently inIndigenous Australianmythology. The bird is sufficiently common for it to be rated as aleast-concern speciesby theInternational Union for Conservation of Nature. Despite this, some local populations are listed as endangered, with subspecies such as theTasmanian emugoing extinct by the 1800s. Threats to their survival include predation of their eggs, roadkills, and fragmentation of their habitats.

The Patagonian mara resembles ajackrabbit.It has distinctive long ears and long limbs. Its hind limbs are longer and more muscular than its fore limbs and it has a longer radius thanhumerus.The feet are compressed, making them hoof-like. The fore feet have four digits while the hind feet have three digits. Its tail is short, depressed, and hairless.It has a gray dorsal pelage with a white patch on the rump separated from the dorsal fur by a black area.In addition, the mara has a white underside with a somewhat orange flank and chin.The average Patagonian mara has a head and body length of 69–75cm (27–30in) with a tail of 4–5cm (1.6–2.0in). It weighs 8–16kg (18–35lb). Unlike most othercaviids, such asguinea pigsandcapybaras, theanal glandsof the mara are between the anus and the base of the tail rather than being anterior to the anus.

Village street dog is very cute.

Dog safari very nice.

Street dog slipping.

Whit cat. Very sweet cat.

One black cat.

Black cat.

The male Taveta weaver is a vibrant golden yellow color; this color is duller on its back. The wings and tail are a greener color, whereas brown spots are located on the chest. The back of the head is red, and the bill, or beak, is black. The female is an olive color with paler streaks. In general, the Taveta weaver is a small bird, around the size of thefinchand closely related to thesparrow.

Therufous hornbill(Buceros hydrocorax), also known as thePhilippine hornbilland locally askalaw(pronounced KAH-lau), is a large species ofhornbillendemic to thePhilippines(the largest hornbill in the country). The are referred by locals as the "clock-of-the-mountains" due to its large booming call which typically occur of every hour. It occurs inmoist tropical lowland forest. They are now considered to be a threatened species and its reasons for decline beinghabitat destruction.huntingandpoachingfor theillegal pet trade.

The red fody is about 5 inches (13cm) in length and weighs 14–19 grams (0.49–0.67oz). The male of the species is bright red with black markings around each eye. Its wings and tail are olive-brown. Its underparts are also red, which distinguishes it from other fodies in areas where it has been introduced. The female fody's upper parts are olive-brown and its underparts are greyish brown.

The culer fish. Fishareaquatic,craniate,gill-bearing animals that lacklimbswithdigits. Included in this definition are the livinghagfish,lampreys, andcartilaginousandbony fishas well as various extinct related groups. Approximately 95% of living fish species are ray-finned fish, belonging to the classActinopterygii, with around 99% of those beingteleosts. Fish Temporal range:535–0Ma PreꞒ Ꞓ O S D C P T J K Pg N Middle Cambrian-Recent Giant grouperswimming amongschoolsof other fishHead-on view of ared lionfishScientific classificationKingdom:AnimaliaPhylum:ChordataClade:OlfactoresSubphylum:VertebrataGroups includedJawless fish†Armoured fish†Spiny sharksCartilaginous fishBony fishRay-finned fishLobe-finned fishCladisticallyincluded but traditionally excluded taxaTetrapods†Conodonts The earliest organisms that can be classified as fish were soft-bodiedchordatesthat first appeared during theCambrianperiod. Although they lacked atrue spine, they possessednotochordswhich allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through thePaleozoicera, diversifying into a wide variety of forms. Many fish of the Paleozoic developedexternal armorthat protected them from predators. The first fish withjawsappeared in theSilurianperiod, after which many (such assharks) became formidable marine predators rather than just the prey ofarthropods. Most fish areectothermic("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers likewhite sharkandtunacan hold a highercore temperature.[1][2]Fish can acoustically communicate with each other, most often in the context of feeding, aggression or courtship.[3] Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g.,charandgudgeon) to theabyssaland evenhadaldepths of the deepest oceans (e.g.,cusk-eelsandsnailfish), although no species has yet been documented in the deepest 25% of the ocean.[4]With 34,300 described species, fish exhibit greater species diversity than any other group of vertebrates.[5] Fish are an important resource for humans worldwide, especiallyas food. Commercial and subsistence fishers hunt fish inwild fisheriesorfarmthem in ponds or in cages in the ocean (inaquaculture). They are also caught byrecreational fishers, kept as pets, raised byfishkeepers, and exhibited in publicaquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies. Tetrapods(amphibians,reptiles,birdsandmammals) emerged withinlobe-finned fishes, socladisticallythey are fish as well. However, traditionally fish (piscesorichthyes) are renderedparaphyleticby excluding the tetrapods, and are therefore not considered a formal taxonomic grouping insystematic biology, unless it is used in thecladisticsense, including tetrapods,[6][7]although usually "vertebrate" is preferred and used for this purpose (fish plus tetrapods) instead. Furthermore,cetaceans, although mammals, have often been considered fish by various cultures and timeperiods. Contents Etymology The word forfishin English and the otherGermanic languages(GermanFisch;Gothicfisks) is inherited fromProto-Germanic, and is related to theLatinpiscisandOld Irishīasc, though the exact root is unknown; some authorities reconstruct anProto-Indo-Europeanroot*peysk-, attested only inItalic,Celtic, andGermanic.[8][9][10][11] The English word once had a much broader usage than its current biological meaning. Names such asstarfish,jellyfish,shellfishandcuttlefishattest to almost any fully aquatic animal (including whales) once beingfish. "Correcting" such names (e.g. tosea star) is an attempt to retroactively apply the current meaning offishto words that were coined when it had a different meaning. Evolution Main article:Evolution of fish Fish, as vertebrata, developed as sister of the tunicata. As the tetrapods emerged deep within the fishes group, as sister of the lungfish, characteristics of fish are typically shared by tetrapods, including having vertebrae and a cranium.  Dunkleosteuswas a gigantic, 10-metre (33ft) longprehistoric fishof class Placodermi.  Lower jaw of the placodermEastmanosteuspustulosus, showing the shearing structures ("teeth") on its oral surface; from theDevonianofWisconsin Early fish from the fossil record are represented by a group of small, jawless, armored fish known asostracoderms. Jawless fish lineages are mostly extinct. An extant clade, thelampreysmay approximate ancient pre-jawed fish. The first jaws are found inPlacodermifossils. They lacked distinct teeth, having instead the oral surfaces of their jaw plates modified to serve the various purposes of teeth. The diversity of jawed vertebrates may indicate the evolutionary advantage of ajawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors. Fish may have evolved from a creature similar to a coral-likesea squirt, whose larvae resemble primitive fish in important ways. The first ancestors of fish may havekept the larval form into adulthood(as some sea squirts do today). Phylogeny Fishes are aparaphyleticgroup: that is, anycladecontaining all fish also contains thetetrapods, which are not fish (though they include fish-shaped forms, such asWhales and Dolphinsor theextinctichthyosaurs, which acquired a fish-like body shape due tosecondary aquatic adaptation, seeevolution of cetaceans). The followingcladogramshowsclades- some with, some withoutextantrelatives - that are traditionally considered as "fishes" (cyanline) and the tetrapods (four-limbed vertebrates), which are mostly terrestrial.Extinctgroups are marked with adagger(†). Vertebrata/ Agnatha/  Hyperoartia(lampreys)    Myxini(hagfish)  Cyclostomes   †Euconodonta     †Pteraspidomorphi    †Thelodonti     †Anaspida     †Galeaspida     †Pituriaspida    †Osteostraci  Gnathostomata  "†Placodermi" (armoured fishes,paraphyletic)[13]     "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)[14]   Chondrichthyes  "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)     Holocephali(ratfish)    Euselachii(sharks,rays)   (cartilaginousfishes)Euteleostomi/  "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)    Actinopterygii  Cladistia(bichirs,reedfish)     Chondrostei(sturgeons,paddlefish)    Neopterygii(includesTeleostei, 96% of living fishspecies)   (ray‑finnedfishes)Sarcopterygii  †Onychodontiformes    Actinistia(coelacanths)  Rhipidistia   †Porolepiformes    Dipnoi(lungfishes)   Tetrapodomorpha/   †Rhizodontimorpha     †Tristichopteridae     †Tiktaalik  Tetrapoda  †Ichthyostega    crown-grouptetrapods  four‑limbedvertebrates   (Choanata) (lobe‑finnedfish)  Osteichthyes  (jawedvertebrates)     "Fishes" Craniata Taxonomy  Leedsichthys,of the subclass Actinopterygii, is the largest known fish, with estimates in 2005 putting its maximum size at 16 metres (52ft). Fishes are aparaphyleticgroup and for this reason, groups such as the classPiscesseen in older reference works are no longer used in formal classifications. Traditional classification divides fish into threeextantclasses, and with extinct forms sometimes classified within the tree, sometimes as their own classes:[15][16] ClassAgnatha(jawless fish) SubclassCyclostomata(hagfishandlampreys) SubclassOstracodermi(armoured jawless fish) † ClassChondrichthyes(cartilaginous fish) SubclassElasmobranchii(sharksandrays) SubclassHolocephali(chimaerasand extinct relatives) ClassPlacodermi(armoured fish) † ClassAcanthodii("spiny sharks", sometimes classified under bony fishes)† ClassOsteichthyes(bony fish) SubclassActinopterygii(ray finned fishes) SubclassSarcopterygii(fleshy finned fishes, ancestors of tetrapods) The above scheme is the one most commonly encountered in non-specialist and general works. Many of the above groups are paraphyletic, in that they have given rise to successive groups: Agnathans are ancestral to Chondrichthyes, who again have given rise to Acanthodiians, the ancestors of Osteichthyes. With the arrival ofphylogenetic nomenclature, the fishes has been split up into a more detailed scheme, with the following major groups: Class Myxini (hagfish) ClassPteraspidomorphi† (early jawless fish) ClassThelodonti† ClassAnaspida† ClassPetromyzontida or Hyperoartia Petromyzontidae (lampreys) ClassConodonta(conodonts) † ClassCephalaspidomorphi† (early jawless fish) (unranked)Galeaspida† (unranked)Pituriaspida† (unranked)Osteostraci† InfraphylumGnathostomata(jawed vertebrates) ClassPlacodermi† (armoured fish) ClassChondrichthyes(cartilaginous fish) ClassAcanthodii† (spiny sharks) SuperclassOsteichthyes(bony fish) ClassActinopterygii(ray-finned fish) SubclassChondrostei OrderAcipenseriformes(sturgeonsandpaddlefishes) OrderPolypteriformes(reedfishesandbichirs). SubclassNeopterygii InfraclassHolostei(garsandbowfins) InfraclassTeleostei(many orders of common fish) ClassSarcopterygii(lobe-finned fish) SubclassActinistia(coelacanths) Subclass Dipnoi (lungfish, sister group to thetetrapods) † – indicates extinct taxon Some palaeontologists contend that becauseConodontaarechordates, they are primitive fish. For a fuller treatment of this taxonomy, see thevertebratearticle. The position ofhagfishin the phylum Chordata is not settled. Phylogenetic research in 1998 and 1999 supported the idea that the hagfish and the lampreys form a natural group, theCyclostomata, that is a sister group of the Gnathostomata.[17][18] The various fish groups account for more than half of vertebrate species. As of 2006,[19]there are almost 28,000 knownextantspecies, of which almost 27,000 are bony fish, with 970sharks, rays, and chimerasand about 108 hagfish and lampreys. A third of these species fall within the nine largest families; from largest to smallest, these families areCyprinidae,Gobiidae,Cichlidae,Characidae,Loricariidae,Balitoridae,Serranidae,Labridae, andScorpaenidae. About 64 families aremonotypic, containing only one species. The final total of extant species may grow to exceed 32,500.[20]Each year, newspeciesare discovered andscientifically described. As of 2016,[21]there are over 32,000 documented species of bony fish and over 1,100 species of cartilaginous fish. Species are lost throughextinction(seebiodiversity crisis). Recent examples are theChinese paddlefishor thesmooth handfish. Diversity Main article:Diversity of fish  Agnatha (Pacific hagfish)  Chondrichthyes (Horn shark)  Actinopterygii (Brown trout)  Sarcopterygii (Coelacanth)  A relative of the seahorses, theleafy seadragon's appendages allow it to camouflage (in the form ofcrypsis) with the surroundingseaweed.  The psychedelicmandarin dragonetis one of only two animal species known to have blue colouring because of cellular pigment.[22] The term "fish" most precisely describes any non-tetrapodcraniate(i.e. an animal with a skull and in most cases a backbone) that hasgillsthroughout life and whose limbs, if any, are in the shape of fins.[23]Unlike groupings such as birds ormammals, fish are not a singlecladebut aparaphyleticcollection oftaxa, includinghagfishes,lampreys,sharks and rays,ray-finned fish,coelacanths, andlungfish.[24][25]Indeed, lungfish and coelacanths are closer relatives oftetrapods(such as mammals, birds,amphibians, etc.) than of other fish such as ray-finned fish or sharks, so thelast common ancestorof all fish is also an ancestor to tetrapods. As paraphyletic groups are no longer recognised in modernsystematic biology, the use of the term "fish" as a biological group must be avoided. Many types ofaquatic animalscommonly referred to as "fish" are not fish in the sense given above; examples includeshellfish,cuttlefish,starfish,crayfishandjellyfish. In earlier times, even biologists did not make a distinction– sixteenth century natural historians classified alsoseals, whales,amphibians,crocodiles, evenhippopotamuses, as well as a host of aquatic invertebrates, as fish.[26]However, according to the definition above, all mammals, includingcetaceanslike whales and dolphins, are not fish. In some contexts, especially inaquaculture, the true fish are referred to asfinfish(orfin fish) to distinguish them from these other animals. A typical fish isectothermic, has astreamlinedbody for rapid swimming, extracts oxygen from water using gills or uses an accessory breathing organ to breathe atmospheric oxygen, has two sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin, and a tail fin, has jaws, has skin that is usually covered withscales, and lays eggs. Each criterion has exceptions.Tuna,swordfish, and some species ofsharksshowsome warm-blooded adaptations– they can heat their bodies significantly above ambient water temperature.[24]Streamlining and swimming performance varies from fish such as tuna,salmon, andjacksthat can cover 10–20 body-lengths per second to species such aseelsandraysthat swim no more than 0.5 body-lengths per second.[27]Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures.Lungfishhave paired lungs similar to those of tetrapods,gouramishave a structure called thelabyrinth organthat performs a similar function, while many catfish, such asCorydorasextract oxygen via the intestine or stomach.[28]Body shape and the arrangement of the fins is highly variable, covering such seemingly un-fishlike forms asseahorses,pufferfish,anglerfish, andgulpers. Similarly, the surface of the skin may be naked (as inmoray eels), or covered with scales of a variety of different types usually defined asplacoid(typical of sharks and rays),cosmoid(fossil lungfish and coelacanths),ganoid(various fossil fish but also livinggarsandbichirs),cycloid, andctenoid(these last two are found on mostbony fish).[29]There are even fish that live mostly on land or lay their eggs on land near water.[30]Mudskippersfeed and interact with one another on mudflats and go underwater to hide in their burrows.[31]A singleundescribed speciesofPhreatobiushas been called a true "land fish" as this worm-like catfish strictly lives among waterloggedleaf litter.[32][33]Many species live inunderground lakes,underground riversoraquifersand are popularly known ascavefish.[34] Fish range in size from the huge 16-metre (52ft)whale sharkto the tiny 8-millimetre (0.3in)stout infantfish. Fishspeciesdiversity is roughly divided equally between marine (oceanic) andfreshwaterecosystems.Coral reefsin theIndo-Pacificconstitute the center of diversity for marine fishes, whereas continental freshwater fishes are most diverse in largeriver basinsoftropical rainforests, especially theAmazon,Congo, andMekongbasins. More than 5,600 fish species inhabitNeotropicalfreshwaters alone, such thatNeotropical fishesrepresent about 10% of allvertebratespecies on the Earth. Exceptionally rich sites in the Amazon basin, such asCantão State Park, can contain more freshwater fish species than occur in all of Europe.[35] The deepest living fish in the ocean so far found is the Mariana snailfish (Pseudoliparis swirei) which lives at deeps of 8,000 meters (26,200 feet) along the Mariana Trench near Guam.[36] Thediversityof living fish (finfish) is unevenly distributed among the various groups, withteleostsmaking up the bulk of living fishes (96%), and over 50% of allvertebratespecies.[21]The followingcladogram[37]shows theevolutionary relationshipsof all groups of living fishes (with their respective diversity[21]) and the four-limbed vertebrates (tetrapods).  Diversityof various groups of fish (and othervertebrates) through time  Lungfishare the closest living relatives oftetrapods(four-limbed vertebrates).  ThebowfinAmia calvais the sole survivor of thehalecomorphclade. Vertebrates  Jawless fish(118 living species:hagfish,lampreys)  Jawedvertebrates  Cartilaginous fishes(>1,100 living species:sharks,rays,chimaeras)  Bonyfishes Lobe-finfishRhipidistia  Tetrapoda(>30,000 living species:amphibians,mammals,reptiles,birds)    Dipnoi(6 living species:lungfish)     Actinistia(2 living species:coelacanths)   Ray-finfish  Cladistia(14 living species:bichirs,reedfish)  Actinopteri  Chondrostei(27 living species:sturgeons,paddlefish)  Neopterygii Holostei  Ginglymodi(7 living species:gars,alligator gars)    Halecomorphi(1 living species:bowfin)     Teleostei(>32,000 living species)           Anatomy and physiology Further information:Fish anatomyandFish physiology  Organs: 1.Liver, 2.Gas bladder, 3.Roe, 4.Pyloric caeca, 5.Stomach, 6.Intestine Respiration See also:Aquatic respiration Gills  Tunagills inside the head. The fish head is oriented snout-downwards, with the view looking towards the mouth. Most fish exchange gases usinggillson either side of thepharynx. Gills consist of threadlike structures calledfilaments. Each filament contains acapillarynetwork that provides a largesurface areafor exchangingoxygenandcarbon dioxide. Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. In some fish, capillary blood flows in the opposite direction to the water, causingcountercurrent exchange. The gills push the oxygen-poor water out through openings in the sides of the pharynx. Some fish, likesharksandlampreys, possess multiple gill openings. However,bony fishhave a single gill opening on each side. This opening is hidden beneath a protective bony cover called anoperculum. Juvenilebichirshave external gills, a very primitive feature that they share with larvalamphibians. Air breathing Fish from multiple groups can live out of the water for extended periods.Amphibious fishsuch as themudskippercan live and move about on land for up to several days,[dubious–discuss]or live in stagnant or otherwise oxygen depleted water. Many such fish can breathe air via a variety of mechanisms. The skin ofanguillid eelsmay absorb oxygen directly. Thebuccal cavityof theelectric eelmay breathe air. Catfish of the familiesLoricariidae,Callichthyidae, andScoloplacidaeabsorb air through their digestive tracts.[38]Lungfish, with the exception of theAustralian lungfish, andbichirshave paired lungs similar to those oftetrapodsand must surface to gulp fresh air through the mouth and pass spent air out through the gills.Garandbowfinhave a vascularized swim bladder that functions in the same way.Loaches,trahiras, and manycatfishbreathe by passing air through the gut. Mudskippers breathe by absorbing oxygen across the skin (similar to frogs). A number of fish have evolved so-called accessory breathing organs that extract oxygen from the air. Labyrinth fish (such asgouramisandbettas) have alabyrinth organabove the gills that performs this function. A few other fish have structures resembling labyrinth organs in form and function, most notablysnakeheads,pikeheads, and theClariidaecatfish family. Breathing air is primarily of use to fish that inhabit shallow, seasonally variable waters where the water's oxygen concentration may seasonally decline. Fish dependent solely on dissolved oxygen, such as perch andcichlids, quickly suffocate, while air-breathers survive for much longer, in some cases in water that is little more than wet mud. At the most extreme, some air-breathing fish are able to survive in damp burrows for weeks without water, entering a state ofaestivation(summertime hibernation) until water returns. Air breathing fish can be divided into obligate air breathers and facultative air breathers. Obligate air breathers, such as theAfrican lungfish,mustbreathe air periodically or they suffocate. Facultative air breathers, such as the catfishHypostomus plecostomus, only breathe air if they need to and will otherwise rely on their gills for oxygen. Most air breathing fish are facultative air breathers that avoid the energetic cost of rising to the surface and the fitness cost of exposure to surface predators.[38] Circulation  Didactic modelof a fish heart Fish have aclosed-loop circulatory system. Theheartpumps the blood in a single loop throughout the body. In most fish, the heart consists of four parts, including two chambers and an entrance and exit.[39]The first part is thesinus venosus, a thin-walled sac that collects blood from the fish'sveinsbefore allowing it to flow to the second part, theatrium, which is a large muscular chamber. The atrium serves as a one-way antechamber, sends blood to the third part,ventricle. The ventricle is another thick-walled, muscular chamber and it pumps the blood, first to the fourth part,bulbus arteriosus, a large tube, and then out of the heart. The bulbus arteriosus connects to theaorta, through which blood flows to the gills for oxygenation. Digestion Jaws allow fish to eat a wide variety of food, including plants and other organisms. Fish ingest food through the mouth and break it down in theesophagus. In the stomach, food is further digested and, in many fish, processed in finger-shaped pouches calledpyloric caeca, which secrete digestiveenzymesand absorb nutrients. Organs such as theliverandpancreasadd enzymes and various chemicals as the food moves through the digestive tract. The intestine completes the process of digestion and nutrient absorption. Excretion As with many aquatic animals, most fish release their nitrogenous wastes asammonia. Some of the wastesdiffusethrough the gills. Blood wastes arefilteredby thekidneys. Saltwater fish tend to lose water because ofosmosis. Their kidneys return water to the body. The reverse happens infreshwater fish: they tend to gain water osmotically. Their kidneys produce dilute urine for excretion. Some fish have specially adapted kidneys that vary in function, allowing them to move from freshwater to saltwater. Scales Main article:Fish scale The scales of fish originate from themesoderm(skin); they may be similar in structure to teeth. Sensory and nervous system  Dorsal view of the brain of therainbow trout Central nervous system Fish typically have quite small brains relative to body size compared with other vertebrates, typically one-fifteenth the brain mass of a similarly sized bird or mammal.[40]However, some fish have relatively large brains, most notablymormyridsandsharks, which have brains about as massive relative to body weight as birds andmarsupials.[41] Fish brains are divided into several regions. At the front are theolfactory lobes, a pair of structures that receive and process signals from thenostrilsvia the twoolfactory nerves.[40]The olfactory lobes are very large in fish that hunt primarily by smell, such as hagfish, sharks, and catfish. Behind the olfactory lobes is the two-lobedtelencephalon, the structural equivalent to thecerebruminhigher vertebrates. In fish the telencephalon is concerned mostly witholfaction.[40]Together these structures form the forebrain. Connecting the forebrain to the midbrain is thediencephalon(in the diagram, this structure is below the optic lobes and consequently not visible). The diencephalon performs functions associated withhormonesandhomeostasis.[40]Thepineal bodylies just above the diencephalon. This structure detects light, maintainscircadianrhythms, and controls color changes.[40] Themidbrain(or mesencephalon) contains the twooptic lobes. These are very large in species that hunt by sight, such asrainbow troutandcichlids.[40] The hindbrain (ormetencephalon) is particularly involved in swimming and balance.[40]The cerebellum is a single-lobed structure that is typically the biggest part of the brain.[40]Hagfish andlampreyshave relatively small cerebellae, while themormyridcerebellum is massive and apparently involved in theirelectrical sense.[40] The brain stem (ormyelencephalon) is the brain's posterior.[40]As well as controlling some muscles and body organs, in bony fish at least, the brain stem governsrespirationandosmoregulation.[40] Sense organs Main article:Sensory systems in fish Most fish possess highly developed sense organs. Nearly all daylight fish have color vision that is at least as good as a human's (seevision in fishes). Many fish also have chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears, many fish may not hear very well. Most fish have sensitive receptors that form thelateral line system, which detects gentle currents and vibrations, and senses the motion of nearby fish and prey.[42]The sense information obtained from the lateral line system can be considered both a sense oftouchandhearing.Blind cave fishnavigate almost entirely through the sensations from their lateral line system.[43]Some fish, such as catfish and sharks, have theampullae of Lorenzini,electroreceptorsthat detect weak electric currents on the order of millivolt.[44]Other fish, like the South American electric fishesGymnotiformes, can produce weak electric currents, which they use in navigation and social communication. Fish orient themselves using landmarks and may use mental maps based on multiple landmarks or symbols. Fish behavior in mazes reveals that they possess spatial memory and visual discrimination.[45] Vision Main article:Vision in fishes Visionis an importantsensory systemfor most species of fish. Fish eyes are similar to those ofterrestrialvertebrateslikebirdsand mammals, but have a moresphericallens. Theirretinasgenerally have bothrodsandcones(forscotopicandphotopic vision), and most species havecolour vision. Some fish can seeultravioletand some can seepolarized light. Amongstjawless fish, thelampreyhas well-developed eyes, while thehagfishhas only primitiveeyespots.[46]Fish vision showsadaptationto their visual environment, for exampledeep sea fisheshave eyes suited to the dark environment. Hearing See also:Hearing in fish Hearingis an important sensory system for most species of fish. Fish sense sound using theirlateral linesand theirears. Cognition Further information:Fish intelligence New research has expanded preconceptions about the cognitive capacities of fish. For example,manta rayshave exhibited behavior linked toself-awarenessinmirror testcases. Placed in front of a mirror, individual rays engaged in contingency testing, that is, repetitive behavior aiming to check whether their reflection's behavior mimics their body movement.[47] Wrasseshave also passed the mirror test in a 2018 scientific study.[48][49] Cases of tool use have also been noticed, notably in theChoerodonfamily, inarcherfishandAtlantic cod.[50] Capacity for pain Further information:Pain in fish Experiments done by William Tavolga provide evidence that fish havepainand fear responses. For instance, in Tavolga's experiments,toadfishgrunted when electrically shocked and over time they came to grunt at the mere sight of an electrode.[51] In 2003, Scottish scientists at theUniversity of Edinburghand the Roslin Institute concluded that rainbow trout exhibit behaviors often associated withpainin other animals.Beevenomandacetic acidinjected into the lips resulted in fish rocking their bodies and rubbing their lips along the sides and floors of their tanks, which the researchers concluded were attempts to relieve pain, similar to what mammals would do.[52][53]Neurons fired in a pattern resembling human neuronal patterns.[53] Professor James D. Rose of theUniversity of Wyomingclaimed the study was flawed since it did not provide proof that fish possess "conscious awareness, particularly a kind of awareness that is meaningfully like ours".[54]Rose argues that since fish brains are so different from human brains, fish are probably not conscious in the manner humans are, so that reactions similar to human reactions to pain instead have other causes. Rose had published a study a year earlier arguing that fish cannot feel pain because their brains lack aneocortex.[55]However, animal behavioristTemple Grandinargues that fish could still have consciousness without a neocortex because "different species can use different brain structures and systems to handle the same functions."[53] Animal welfare advocates raise concerns about the possiblesufferingof fish caused by angling. Some countries, such as Germany, have banned specific types of fishing, and the BritishRSPCAnow formally prosecutes individuals who are cruel to fish.[56] Emotion In 2019, scientists have shown that members of themonogamousspeciesAmatitlania siquiaexhibit pessimistic behavior when they are prevented from being with their partner.[57] Muscular system Main article:Fish locomotion  The anatomy ofLampanyctodes hectoris(1)operculum (gill cover), (2)lateral line, (3)dorsal fin, (4)fat fin, (5)caudal peduncle, (6)caudal fin, (7)anal fin, (8)photophores, (9)pelvic fins (paired), (10)pectoral fins (paired)  Swim bladder of a rudd (Scardinius erythrophthalmus) Most fish move by alternately contracting paired sets of muscles on either side of the backbone. These contractions form S-shaped curves that move down the body. As each curve reaches the back fin, backward force is applied to the water, and in conjunction with the fins, moves the fish forward. The fish's fins function like an airplane's flaps. Fins also increase the tail's surface area, increasing speed. The streamlined body of the fish decreases the amount of friction from the water. Since body tissue is denser than water, fish must compensate for the difference or they will sink. Many bony fish have an internal organ called aswim bladderthat adjusts their buoyancy through manipulation of gases. Endothermy Although most fish are exclusivelyectothermic, there are exceptions. The only known bony fishes (infraclassTeleostei) that exhibitendothermyare in the suborderScombroidei– which includes thebillfishes, tunas, and thebutterfly kingfish, abasalspecies of mackerel[58]– and also theopah. The opah, alampriform, was demonstrated in 2015 to utilize "whole-body endothermy", generating heat with its swimming muscles to warm its body while countercurrent exchange (as in respiration) minimizes heat loss.[59]It is able to actively hunt prey such as squid and swim for long distances due to the ability to warm its entire body, including its heart,[60]which is a trait typically found in only mammals and birds (in the form ofhomeothermy). In the cartilaginous fishes (classChondrichthyes), sharks of the familiesLamnidae(porbeagle, mackerel, salmon, and great white sharks) andAlopiidae(thresher sharks) exhibit endothermy. The degree of endothermy varies from the billfishes, which warm only their eyes and brain, to thebluefin tunaand theporbeagle shark, which maintain body temperatures in excess of 20°C (68°F) above ambient water temperatures.[58] Endothermy, though metabolically costly, is thought to provide advantages such as increased muscle strength, higher rates of centralnervous systemprocessing, and higher rates ofdigestion. Reproductive system Further information:Fish reproductionandSpawn (biology)  Ovary of fish (Corumbatá) Fish reproductive organs includetesticlesandovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused.[61]There may also be a range of secondary organs that increase reproductive fitness. In terms ofspermatogoniadistribution, the structure ofteleoststestes has two types: in the most common, spermatogonia occur all along theseminiferous tubules, while inatherinomorphfish they are confined to thedistalportion of these structures. Fish can present cystic or semi-cysticspermatogenesisin relation to the release phase of germ cells in cysts to the seminiferous tubuleslumen.[61] Fish ovaries may be of three types: gymnovarian, secondary gymnovarian or cystovarian. In the first type, theoocytesare released directly into thecoelomiccavity and then enter theostium, then through theoviductand are eliminated. Secondary gymnovarian ovaries shedovainto the coelom from which they go directly into the oviduct. In the third type, the oocytes are conveyed to the exterior through the oviduct.[62]Gymnovaries are the primitive condition found inlungfish,sturgeon, andbowfin. Cystovaries characterize most teleosts, where the ovary lumen has continuity with the oviduct.[61]Secondary gymnovaries are found insalmonidsand a few other teleosts. Oogoniadevelopment in teleosts fish varies according to the group, and the determination of oogenesis dynamics allows the understanding of maturation and fertilization processes. Changes in thenucleus, ooplasm, and the surrounding layers characterize the oocyte maturation process.[61] Postovulatoryfolliclesare structures formed after oocyte release; they do not haveendocrinefunction, present a wide irregular lumen, and are rapidly reabsorbed in a process involving theapoptosisof follicular cells. A degenerative process calledfollicular atresiareabsorbs vitellogenic oocytes not spawned. This process can also occur, but less frequently, in oocytes in other development stages.[61] Some fish, like theCalifornia sheephead, arehermaphrodites, having both testes and ovaries either at different phases in their life cycle or, as inhamlets, have them simultaneously. Over 97% of all known fish areoviparous,[63]that is, the eggs develop outside the mother's body. Examples of oviparous fish includesalmon,goldfish,cichlids,tuna, andeels. In the majority of these species, fertilisation takes place outside the mother's body, with the male and female fish shedding theirgametesinto the surrounding water. However, a few oviparous fish practice internal fertilization, with the male using some sort ofintromittent organto deliver sperm into the genital opening of the female, most notably the oviparous sharks, such as thehorn shark, and oviparous rays, such asskates. In these cases, the male is equipped with a pair of modifiedpelvic finsknown asclaspers. Marine fish can produce high numbers of eggs which are often released into the open water column. The eggs have an average diameter of 1 millimetre (0.04in).  Egg oflamprey  Egg ofcatshark(mermaids' purse)  Egg ofbullhead shark  Egg ofchimaera The newly hatched young of oviparous fish are calledlarvae. They are usually poorly formed, carry a largeyolk sac(for nourishment), and are very different in appearance from juvenile and adult specimens. The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termedmetamorphosis) to become juveniles. During this transition larvae must switch from their yolk sac to feeding onzooplanktonprey, a process which depends on typically inadequate zooplankton density, starving many larvae. Inovoviviparousfish the eggs develop inside the mother's body after internal fertilization but receive little or no nourishment directly from the mother, depending instead on theyolk. Each embryo develops in its own egg. Familiar examples of ovoviviparous fish includeguppies,angel sharks, andcoelacanths. Some species of fish areviviparous. In such species the mother retains the eggs and nourishes the embryos. Typically, viviparous fish have a structure analogous to theplacentaseen inmammalsconnecting the mother's blood supply with that of the embryo. Examples of viviparous fish include thesurf-perches,splitfins, andlemon shark. Some viviparous fish exhibitoophagy, in which the developing embryos eat other eggs produced by the mother. This has been observed primarily among sharks, such as theshortfin makoandporbeagle, but is known for a few bony fish as well, such as thehalfbeakNomorhamphus ebrardtii.[64]Intrauterine cannibalismis an even more unusual mode of vivipary, in which the largest embryos eat weaker and smaller siblings. This behavior is also most commonly found among sharks, such as thegrey nurse shark, but has also been reported forNomorhamphus ebrardtii.[64] Aquaristscommonly refer to ovoviviparous and viviparous fish aslivebearers. Acoustic communication See also:Acoustic communication in aquatic animals Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another. The production of sounds as a means of communication among fish is most often used in the context of feeding, aggression or courtship behaviour.[3]The sounds emitted can vary depending on the species and stimulus involved. Fish can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder.[65] Stridulatory  French grunts –Haemulon flavolineatum There are some species of fish that can produce sounds by rubbing or grinding their bones together. These noises produced by bone-on-bone interactions are known as 'stridulatory sounds'.[65] An example of this is seen inHaemulon flavolineatum, a species commonly referred to as the 'French grunt fish', as it produces a grunting noise by grinding its teeth together.[65]This behaviour is most pronounced when theH. flavolineatumis in distress situations.[65]The grunts produced by this species of fishes generate a frequency of approximately 700Hz, and last approximately 47 milliseconds.[65]TheH. flavolineatumdoes not emit sounds with frequencies greater than 1000Hz, and does not detect sounds that have frequencies greater than 1050Hz.[65] In a study conducted by Oliveira et al. (2014), the longsnout seahorse,Hippocampus reidi, was recorded producing two different categories of sounds; 'clicks' and 'growls'. The sounds emitted by theH. reidiare accomplished by rubbing their coronet bone across the grooved section of their neurocranium.[66]'Clicking' sounds were found to be primarily produced during courtship and feeding, and the frequencies of clicks were within the range of 50Hz-800Hz.[67]The frequencies were noted to be on the higher end of the range during spawning periods, when the female and male fishes were less than fifteen centimeters apart.[67]Growl sounds were produced when theH. reidiencountered stressful situations, such as handling by researchers.[67]The 'growl' sounds consist of a series of sound pulses and are emitted simultaneously with body vibrations.[67] Non-stridulatory  Oyster toadfish Some fish species create noise by engaging specialized muscles that contract and cause swimbladder vibrations. Oyster toadfishproduce loud grunting sounds by contracting muscles located along the sides of their swim bladder, known as sonic muscles[68]Female and male toadfishes emit short-duration grunts, often as a fright response.[69]In addition to short-duration grunts, male toadfishes produce "boat whistle calls".[70]These calls are longer in duration, lower in frequency, and are primarily used to attract mates.[70]The sounds emitted by theO. taohave frequency range of 140Hz to 260Hz.[70]The frequencies of the calls depend on the rate at which the sonic muscles contract.[71][68] The red drum,Sciaenops ocellatus, produces drumming sounds by vibrating its swimbladder.[72]Vibrations are caused by the rapid contraction of sonic muscles that surround the dorsal aspect of the swimbladder.[72]These vibrations result in repeated sounds with frequencies that range from 100 to >200Hz.[72]TheS. ocellatuscan produce different calls depending on the stimuli involved.[72]The sounds created in courtship situations are different from those made during distressing events such as predatorial attacks.[72]Unlike the males of theS. ocellatusspecies, the females of this species do not produce sounds and lack sound-producing (sonic) muscles.[72] Diseases Main article:Fish diseases and parasites Like other animals, fish suffer from diseases and parasites. To prevent disease they have a variety of defenses.Non-specificdefenses include the skin and scales, as well as the mucus layer secreted by theepidermisthat traps and inhibits the growth ofmicroorganisms. Ifpathogensbreach these defenses, fish can develop aninflammatory responsethat increases blood flow to the infected region and deliverswhite blood cellsthat attempt to destroy pathogens. Specific defenses respond to particular pathogens recognised by the fish's body, i.e., animmune response.[73]In recent years,vaccineshave become widely used in aquaculture and also with ornamental fish, for examplefurunculosisvaccines in farmedsalmonandkoi herpes virusinkoi.[74][75] Some species usecleaner fishto remove external parasites. The best known of these are thebluestreak cleaner wrassesof the genusLabroidesfound oncoral reefsin theIndianandPacificoceans. These small fish maintain so-called "cleaning stations" where other fish congregate and perform specific movements to attract the attention of the cleaners.[76]Cleaning behaviors have been observed in a number of fish groups, including an interesting case between two cichlids of the same genus,Etroplus maculatus, the cleaner, and the much largerEtroplus suratensis.[77] Immune system Immune organs vary by type of fish.[78]In thejawless fish(lampreys and hagfish), truelymphoidorgans are absent. These fish rely on regions oflymphoid tissuewithin other organs to produce immune cells. For example,erythrocytes,macrophagesandplasma cellsare produced in the anterior kidney (orpronephros) and some areas of the gut (wheregranulocytesmature.) They resemble primitivebone marrowin hagfish.Cartilaginous fish(sharks and rays) have a more advanced immune system. They have three specialized organs that are unique toChondrichthyes; the epigonal organs (lymphoid tissue similar to mammalian bone) that surround the gonads, theLeydig's organwithin the walls of their esophagus, and aspiral valvein their intestine. These organs house typical immune cells (granulocytes, lymphocytes and plasma cells). They also possess an identifiablethymusand a well-developedspleen(their most important immune organ) where variouslymphocytes, plasma cells and macrophages develop and are stored.Chondrosteanfish (sturgeons, paddlefish, and bichirs) possess a major site for the production of granulocytes within a mass that is associated with themeninges(membranes surrounding the central nervous system.) Their heart is frequently covered with tissue that contains lymphocytes,reticular cellsand a small number ofmacrophages. The chondrostean kidney is an importanthemopoieticorgan; where erythrocytes, granulocytes, lymphocytes and macrophages develop. Like chondrostean fish, the major immune tissues of bony fish (orteleostei) include the kidney (especially the anterior kidney), which houses many different immune cells.[79]In addition, teleost fish possess a thymus, spleen and scattered immune areas within mucosal tissues (e.g. in the skin, gills, gut and gonads). Much like the mammalian immune system, teleost erythrocytes, neutrophils and granulocytes are believed to reside in the spleen whereas lymphocytes are the major cell type found in the thymus.[80][81]In 2006, a lymphatic system similar to that in mammals was described in one species of teleost fish, thezebrafish. Although not confirmed as yet, this system presumably will be where naive (unstimulated)T cellsaccumulate while waiting to encounter anantigen.[82] B and T lymphocytes bearingimmunoglobulinsandT cell receptors, respectively, are found in all jawed fishes. Indeed, theadaptive immune systemas a wholeevolvedin an ancestor of all jawed vertebrates.[83] Conservation The 2006IUCNRed Listnames 1,173 fish species that are threatened with extinction.[84]Included are species such asAtlantic cod,[85]Devil's Hole pupfish,[86]coelacanths,[87]andgreat white sharks.[88]Because fish live underwater they are more difficult to study than terrestrial animals and plants, and information about fish populations is often lacking. However, freshwater fish seem particularly threatened because they often live in relatively small water bodies. For example, theDevil's Hole pupfishoccupies only a single 3 by 6 metres (10 by 20ft) pool.[89] Overfishing  Whale sharks, the largest species of fish, are classified asvulnerable. Main article:Overfishing Overfishing is a major threat to edible fish such as cod andtuna.[90][91]Overfishing eventually causespopulation(known asstock) collapse because the survivors cannot produce enough young to replace those removed. Suchcommercial extinctiondoes not mean that the species is extinct, merely that it can no longer sustain a fishery. One well-studied example of fishery collapse is thePacific sardineSadinops sagax caeruluesfishery off the California coast. From a 1937 peak of 790,000 long tons (800,000t) the catch steadily declined to only 24,000 long tons (24,000t) in 1968, after which the fishery was no longer economically viable.[92] The main tension betweenfisheries scienceand thefishing industryis that the two groups have different views on the resiliency of fisheries to intensive fishing. In places such as Scotland, Newfoundland, and Alaska the fishing industry is a major employer, so governments are predisposed to support it.[93][94]On the other hand, scientists and conservationists push for stringent protection, warning that many stocks could be wiped out within fifty years.[95][96] Habitat destruction See also:Environmental impact of fishing A key stress on both freshwater and marine ecosystems is habitat degradation includingwater pollution, the building of dams, removal of water for use by humans, and the introduction ofexoticspecies.[97]An example of a fish that has become endangered because of habitat change is thepallid sturgeon, a North American freshwater fish that lives in rivers damaged by human activity.[98] Exotic species Introduction ofnon-nativespecies has occurred in many habitats. One of the best studied examples is the introduction ofNile perchintoLake Victoriain the 1960s. Nile perch gradually exterminated the lake's 500endemiccichlidspecies. Some of them survive now in captive breeding programmes, but others are probably extinct.[99]Carp,snakeheads,[100]tilapia,European perch,brown trout,rainbow trout, andsea lampreysare other examples of fish that have caused problems by being introduced into alien environments. Importance to humans Economic Main articles:Fishing industry,Aquaculture, andFish farming  These fish-farming ponds were created as acooperativeproject in a rural village. Throughout history, humans have utilizedfish as a food source. Historically and today, most fishproteinhas come by means of catching wild fish. However, aquaculture, or fish farming, which has been practiced since about 3,500 BCE. in China,[101]is becoming increasingly important in many nations. Overall, about one-sixth of the world's protein is estimated to be provided by fish.[102]That proportion is considerably elevated in somedeveloping nationsand regions heavily dependent on the sea. In a similar manner, fish have been tied to trade.  Fish counter display at theOulu Market HallinOulu, Finland. Catching fish for the purpose of food or sport is known asfishing, while the organized effort by humans to catch fish is called afishery. Fisheries are a huge global business and provide income for millions of people.[102]The annual yield from all fisheries worldwide is about 154 million tons,[103]with popular species includingherring,cod,anchovy,tuna,flounder, andsalmon. However, the term fishery is broadly applied, and includes more organisms than just fish, such asmollusksandcrustaceans, which are often called "fish" when used as food. Recreation  ABengalifish vendor Main articles:Fishkeeping,Recreational fishing, andAngling Fishkeeping Fish have been recognized as a source of beauty for almost as long as used for food, appearing incave art, being raised asornamental fishin ponds, and displayed inaquariumsin homes, offices, or public settings. Recreational fishing Recreational fishingis fishing primarily for pleasure or competition; it can be contrasted withcommercial fishing, which is fishing for profit, orartisanal fishing, which is fishing primarily for food. The most common form of recreational fishing is done with arod,reel,line,hooks, and any one of a wide range ofbaits. Recreational fishing is particularly popular in North America and Europe and state, provincial, and federal government agencies actively management target fish species.[104][105]Angling is a method of fishing, specifically the practice of catching fish by means of an "angle" (hook). Anglers must select the right hook,castaccurately, and retrieve at the right speed while considering water and weather conditions, species, fish response, time of the day, and other factors. Culture Main article:Fish in culture  AvatarofVishnuas aMatsya Fish themes have symbolic significance in many religions. In ancientMesopotamia, fish offerings were made to the gods from the very earliest times.[106]Fish were also a major symbol ofEnki, the god of water.[106]Fish frequently appear as filling motifs incylinder sealsfrom theOld Babylonian(c.1830 BC –c.1531 BC) andNeo-Assyrian(911–609 BC) periods.[106]Starting during theKassite Period(c.1600 BC –c.1155 BC) and lasting until the earlyPersian Period(550–30 BC), healers and exorcists dressed in ritual garb resembling the bodies of fish.[106]During theSeleucid Period(312–63 BC), the legendary Babylonianculture heroOannes, described byBerossus, was said to have dressed in the skin of a fish.[106]Fish were sacred to the Syrian goddessAtargatis[107]and, during her festivals, only her priests were permitted to eat them.[107]  Theichthusis a Christian symbol of a fish signifying that the person who uses it is a Christian.[107][108] In theBook of Jonah, a work of Jewish literature probably written in the fourth century BC, the central figure, aprophetnamedJonah, is swallowed by a giant fish after being thrown overboard by the crew of the ship he is travelling on.[109][110][111]The fish later vomits Jonah out on shore after three days.[109][110][111]This book was later included as part of theHebrew Bible, or ChristianOld Testament,[112][113]and a version of the story it contains is summarized inSurah37:139-148 of theQuran.[114]Early Christiansused theichthys, a symbol of a fish, to represent Jesus,[107][108]because the Greek word for fish, ΙΧΘΥΣ Ichthys, could be used as an acronym for "Ίησοῦς Χριστός, Θεοῦ Υἱός, Σωτήρ" (Iesous Christos, Theou Huios, Soter), meaning "Jesus Christ, Son of God, Saviour".[107][108]Thegospelsalso refer to "fishers of men"[115]andfeeding the multitude. In thedhammaofBuddhism, the fish symbolize happiness as they have complete freedom of movement in the water. Often drawn in the form ofcarpwhich are regarded in the Orient as sacred on account of their elegant beauty, size and life-span. Among thedeitiessaid to take the form of a fish areIka-Roaof thePolynesians,Dagonof various ancientSemitic peoples, the shark-gods ofHawaiʻiandMatsyaof the Hindus. TheastrologicalsymbolPiscesis based on a constellation of thesame name, but there is also a second fish constellation in the night sky,Piscis Austrinus.[116] Fish feature prominently in art and literature, in movies such asFinding Nemoand books such asThe Old Man and the Sea. Large fish, particularly sharks, have frequently been the subject ofhorror moviesandthrillers, most notably the novelJaws, which spawned a series of films of thesame namethat in turn inspired similar films or parodies such asShark TaleandSnakehead Terror. Piranhas are shown in a similar light to sharks in films such asPiranha; however, contrary to popular belief, thered-bellied piranhais actually a generally timid scavenger species that is unlikely to harm humans.[117]Legends of half-human, half-fishmermaidshave featured in folklore, including the stories ofHans Christian Andersen. Terminology "Fish" or "fishes" Though often used interchangeably, in biology these words have different meanings.Fishis used as a singular noun, or as a plural to describe multiple individuals from a single species.Fishesis used to describe different species or species groups.[118][119][120]Thus a pond would be said to contain 120 fish if all were from a single species or 120 fishes if these included a mix of several species. The distinction is similar to that between people and peoples. "True fish" or "finfish" In biology, the termfishis most strictly used to describe any animal with abackbone,gillsthroughout life, and limbs (if any) in the shape offins.[23]Many types ofaquatic animalswith common names ending in "fish" are not fish in thissense; examples includeshellfish,cuttlefish,starfish,crayfishandjellyfish. In earlier times, even biologists did not make a distinction– sixteenth century natural historians classified alsoseals, whales,amphibians,crocodiles, evenhippopotamuses, as well as a host of aquatic invertebrates, as fish.[26] In fisheries, the termfishis used as a collective term, and includesmollusks,crustaceansand anyaquatic animalwhich is harvested.[121] The strict biological definition of a fish, above, is sometimes called atrue fish. True fish are also referred to asfinfishorfin fishto distinguish them from other aquatic life harvested in fisheries or aquaculture. "Shoal" or "school" Main article:Shoaling and schooling  Thesegoldband fusiliersareschoolingbecause their swimming is synchronised. An assemblage of fish merely using some localised resource such as food or nesting sites is known simply as anaggregation. When fish come together in an interactive, social grouping, then they may be forming either ashoalor aschooldepending on the degree of organisation. Ashoalis a loosely organised group where each fish swims and forages independently but is attracted to other members of the group and adjusts its behaviour, such as swimming speed, so that it remains close to the other members of the group.Schoolsof fish are much more tightly organised, synchronising their swimming so that all fish move at the same speed and in the same direction. Shoaling and schooling behaviour is believed to provide a variety of advantages.[122] Examples: Cichlids congregating atlekkingsites form anaggregation. Many minnows and characins formshoals. Anchovies, herrings and silversides are classic examples ofschoolingfish. The most common collective nouns for a group of fish in general are school and shoal. Both the words have evolved from the same common Dutch root 'schole' meaning a troop or crowd. While the words "school" and "shoal" have different meanings within biology, the distinctions are often ignored by non-specialists who treat the words assynonyms. Thus speakers ofBritish Englishcommonly use "shoal" to describe any grouping of fish, and speakers ofAmerican Englishcommonly use "school" just as loosely.[123]

Fishareaquatic,craniate,gill-bearing animals that lacklimbswithdigits. Included in this definition are the livinghagfish,lampreys, andcartilaginousandbony fishas well as various extinct related groups. Approximately 95% of living fish species are ray-finned fish, belonging to the classActinopterygii, with around 99% of those beingteleosts. Fish Temporal range:535–0Ma PreꞒ Ꞓ O S D C P T J K Pg N Middle Cambrian-Recent Giant grouperswimming amongschoolsof other fishHead-on view of ared lionfishScientific classificationKingdom:AnimaliaPhylum:ChordataClade:OlfactoresSubphylum:VertebrataGroups includedJawless fish†Armoured fish†Spiny sharksCartilaginous fishBony fishRay-finned fishLobe-finned fishCladisticallyincluded but traditionally excluded taxaTetrapods†Conodonts The earliest organisms that can be classified as fish were soft-bodiedchordatesthat first appeared during theCambrianperiod. Although they lacked atrue spine, they possessednotochordswhich allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through thePaleozoicera, diversifying into a wide variety of forms. Many fish of the Paleozoic developedexternal armorthat protected them from predators. The first fish withjawsappeared in theSilurianperiod, after which many (such assharks) became formidable marine predators rather than just the prey ofarthropods. Most fish areectothermic("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers likewhite sharkandtunacan hold a highercore temperature.[1][2]Fish can acoustically communicate with each other, most often in the context of feeding, aggression or courtship.[3] Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g.,charandgudgeon) to theabyssaland evenhadaldepths of the deepest oceans (e.g.,cusk-eelsandsnailfish), although no species has yet been documented in the deepest 25% of the ocean.[4]With 34,300 described species, fish exhibit greater species diversity than any other group of vertebrates.[5] Fish are an important resource for humans worldwide, especiallyas food. Commercial and subsistence fishers hunt fish inwild fisheriesorfarmthem in ponds or in cages in the ocean (inaquaculture). They are also caught byrecreational fishers, kept as pets, raised byfishkeepers, and exhibited in publicaquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies. Tetrapods(amphibians,reptiles,birdsandmammals) emerged withinlobe-finned fishes, socladisticallythey are fish as well. However, traditionally fish (piscesorichthyes) are renderedparaphyleticby excluding the tetrapods, and are therefore not considered a formal taxonomic grouping insystematic biology, unless it is used in thecladisticsense, including tetrapods,[6][7]although usually "vertebrate" is preferred and used for this purpose (fish plus tetrapods) instead. Furthermore,cetaceans, although mammals, have often been considered fish by various cultures and timeperiods. Contents Etymology The word forfishin English and the otherGermanic languages(GermanFisch;Gothicfisks) is inherited fromProto-Germanic, and is related to theLatinpiscisandOld Irishīasc, though the exact root is unknown; some authorities reconstruct anProto-Indo-Europeanroot*peysk-, attested only inItalic,Celtic, andGermanic.[8][9][10][11] The English word once had a much broader usage than its current biological meaning. Names such asstarfish,jellyfish,shellfishandcuttlefishattest to almost any fully aquatic animal (including whales) once beingfish. "Correcting" such names (e.g. tosea star) is an attempt to retroactively apply the current meaning offishto words that were coined when it had a different meaning. Evolution Main article:Evolution of fish Fish, as vertebrata, developed as sister of the tunicata. As the tetrapods emerged deep within the fishes group, as sister of the lungfish, characteristics of fish are typically shared by tetrapods, including having vertebrae and a cranium.  Dunkleosteuswas a gigantic, 10-metre (33ft) longprehistoric fishof class Placodermi.  Lower jaw of the placodermEastmanosteuspustulosus, showing the shearing structures ("teeth") on its oral surface; from theDevonianofWisconsin Early fish from the fossil record are represented by a group of small, jawless, armored fish known asostracoderms. Jawless fish lineages are mostly extinct. An extant clade, thelampreysmay approximate ancient pre-jawed fish. The first jaws are found inPlacodermifossils. They lacked distinct teeth, having instead the oral surfaces of their jaw plates modified to serve the various purposes of teeth. The diversity of jawed vertebrates may indicate the evolutionary advantage of ajawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors. Fish may have evolved from a creature similar to a coral-likesea squirt, whose larvae resemble primitive fish in important ways. The first ancestors of fish may havekept the larval form into adulthood(as some sea squirts do today). Phylogeny Fishes are aparaphyleticgroup: that is, anycladecontaining all fish also contains thetetrapods, which are not fish (though they include fish-shaped forms, such asWhales and Dolphinsor theextinctichthyosaurs, which acquired a fish-like body shape due tosecondary aquatic adaptation, seeevolution of cetaceans). The followingcladogramshowsclades- some with, some withoutextantrelatives - that are traditionally considered as "fishes" (cyanline) and the tetrapods (four-limbed vertebrates), which are mostly terrestrial.Extinctgroups are marked with adagger(†). Vertebrata/ Agnatha/  Hyperoartia(lampreys)    Myxini(hagfish)  Cyclostomes   †Euconodonta     †Pteraspidomorphi    †Thelodonti     †Anaspida     †Galeaspida     †Pituriaspida    †Osteostraci  Gnathostomata  "†Placodermi" (armoured fishes,paraphyletic)[13]     "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)[14]   Chondrichthyes  "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)     Holocephali(ratfish)    Euselachii(sharks,rays)   (cartilaginousfishes)Euteleostomi/  "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)    Actinopterygii  Cladistia(bichirs,reedfish)     Chondrostei(sturgeons,paddlefish)    Neopterygii(includesTeleostei, 96% of living fishspecies)   (ray‑finnedfishes)Sarcopterygii  †Onychodontiformes    Actinistia(coelacanths)  Rhipidistia   †Porolepiformes    Dipnoi(lungfishes)   Tetrapodomorpha/   †Rhizodontimorpha     †Tristichopteridae     †Tiktaalik  Tetrapoda  †Ichthyostega    crown-grouptetrapods  four‑limbedvertebrates   (Choanata) (lobe‑finnedfish)  Osteichthyes  (jawedvertebrates)     "Fishes" Craniata Taxonomy  Leedsichthys,of the subclass Actinopterygii, is the largest known fish, with estimates in 2005 putting its maximum size at 16 metres (52ft). Fishes are aparaphyleticgroup and for this reason, groups such as the classPiscesseen in older reference works are no longer used in formal classifications. Traditional classification divides fish into threeextantclasses, and with extinct forms sometimes classified within the tree, sometimes as their own classes:[15][16] ClassAgnatha(jawless fish) SubclassCyclostomata(hagfishandlampreys) SubclassOstracodermi(armoured jawless fish) † ClassChondrichthyes(cartilaginous fish) SubclassElasmobranchii(sharksandrays) SubclassHolocephali(chimaerasand extinct relatives) ClassPlacodermi(armoured fish) † ClassAcanthodii("spiny sharks", sometimes classified under bony fishes)† ClassOsteichthyes(bony fish) SubclassActinopterygii(ray finned fishes) SubclassSarcopterygii(fleshy finned fishes, ancestors of tetrapods) The above scheme is the one most commonly encountered in non-specialist and general works. Many of the above groups are paraphyletic, in that they have given rise to successive groups: Agnathans are ancestral to Chondrichthyes, who again have given rise to Acanthodiians, the ancestors of Osteichthyes. With the arrival ofphylogenetic nomenclature, the fishes has been split up into a more detailed scheme, with the following major groups: Class Myxini (hagfish) ClassPteraspidomorphi† (early jawless fish) ClassThelodonti† ClassAnaspida† ClassPetromyzontida or Hyperoartia Petromyzontidae (lampreys) ClassConodonta(conodonts) † ClassCephalaspidomorphi† (early jawless fish) (unranked)Galeaspida† (unranked)Pituriaspida† (unranked)Osteostraci† InfraphylumGnathostomata(jawed vertebrates) ClassPlacodermi† (armoured fish) ClassChondrichthyes(cartilaginous fish) ClassAcanthodii† (spiny sharks) SuperclassOsteichthyes(bony fish) ClassActinopterygii(ray-finned fish) SubclassChondrostei OrderAcipenseriformes(sturgeonsandpaddlefishes) OrderPolypteriformes(reedfishesandbichirs). SubclassNeopterygii InfraclassHolostei(garsandbowfins) InfraclassTeleostei(many orders of common fish) ClassSarcopterygii(lobe-finned fish) SubclassActinistia(coelacanths) Subclass Dipnoi (lungfish, sister group to thetetrapods) † – indicates extinct taxon Some palaeontologists contend that becauseConodontaarechordates, they are primitive fish. For a fuller treatment of this taxonomy, see thevertebratearticle. The position ofhagfishin the phylum Chordata is not settled. Phylogenetic research in 1998 and 1999 supported the idea that the hagfish and the lampreys form a natural group, theCyclostomata, that is a sister group of the Gnathostomata.[17][18] The various fish groups account for more than half of vertebrate species. As of 2006,[19]there are almost 28,000 knownextantspecies, of which almost 27,000 are bony fish, with 970sharks, rays, and chimerasand about 108 hagfish and lampreys. A third of these species fall within the nine largest families; from largest to smallest, these families areCyprinidae,Gobiidae,Cichlidae,Characidae,Loricariidae,Balitoridae,Serranidae,Labridae, andScorpaenidae. About 64 families aremonotypic, containing only one species. The final total of extant species may grow to exceed 32,500.[20]Each year, newspeciesare discovered andscientifically described. As of 2016,[21]there are over 32,000 documented species of bony fish and over 1,100 species of cartilaginous fish. Species are lost throughextinction(seebiodiversity crisis). Recent examples are theChinese paddlefishor thesmooth handfish. Diversity Main article:Diversity of fish  Agnatha (Pacific hagfish)  Chondrichthyes (Horn shark)  Actinopterygii (Brown trout)  Sarcopterygii (Coelacanth)  A relative of the seahorses, theleafy seadragon's appendages allow it to camouflage (in the form ofcrypsis) with the surroundingseaweed.  The psychedelicmandarin dragonetis one of only two animal species known to have blue colouring because of cellular pigment.[22] The term "fish" most precisely describes any non-tetrapodcraniate(i.e. an animal with a skull and in most cases a backbone) that hasgillsthroughout life and whose limbs, if any, are in the shape of fins.[23]Unlike groupings such as birds ormammals, fish are not a singlecladebut aparaphyleticcollection oftaxa, includinghagfishes,lampreys,sharks and rays,ray-finned fish,coelacanths, andlungfish.[24][25]Indeed, lungfish and coelacanths are closer relatives oftetrapods(such as mammals, birds,amphibians, etc.) than of other fish such as ray-finned fish or sharks, so thelast common ancestorof all fish is also an ancestor to tetrapods. As paraphyletic groups are no longer recognised in modernsystematic biology, the use of the term "fish" as a biological group must be avoided. Many types ofaquatic animalscommonly referred to as "fish" are not fish in the sense given above; examples includeshellfish,cuttlefish,starfish,crayfishandjellyfish. In earlier times, even biologists did not make a distinction– sixteenth century natural historians classified alsoseals, whales,amphibians,crocodiles, evenhippopotamuses, as well as a host of aquatic invertebrates, as fish.[26]However, according to the definition above, all mammals, includingcetaceanslike whales and dolphins, are not fish. In some contexts, especially inaquaculture, the true fish are referred to asfinfish(orfin fish) to distinguish them from these other animals. A typical fish isectothermic, has astreamlinedbody for rapid swimming, extracts oxygen from water using gills or uses an accessory breathing organ to breathe atmospheric oxygen, has two sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin, and a tail fin, has jaws, has skin that is usually covered withscales, and lays eggs. Each criterion has exceptions.Tuna,swordfish, and some species ofsharksshowsome warm-blooded adaptations– they can heat their bodies significantly above ambient water temperature.[24]Streamlining and swimming performance varies from fish such as tuna,salmon, andjacksthat can cover 10–20 body-lengths per second to species such aseelsandraysthat swim no more than 0.5 body-lengths per second.[27]Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures.Lungfishhave paired lungs similar to those of tetrapods,gouramishave a structure called thelabyrinth organthat performs a similar function, while many catfish, such asCorydorasextract oxygen via the intestine or stomach.[28]Body shape and the arrangement of the fins is highly variable, covering such seemingly un-fishlike forms asseahorses,pufferfish,anglerfish, andgulpers. Similarly, the surface of the skin may be naked (as inmoray eels), or covered with scales of a variety of different types usually defined asplacoid(typical of sharks and rays),cosmoid(fossil lungfish and coelacanths),ganoid(various fossil fish but also livinggarsandbichirs),cycloid, andctenoid(these last two are found on mostbony fish).[29]There are even fish that live mostly on land or lay their eggs on land near water.[30]Mudskippersfeed and interact with one another on mudflats and go underwater to hide in their burrows.[31]A singleundescribed speciesofPhreatobiushas been called a true "land fish" as this worm-like catfish strictly lives among waterloggedleaf litter.[32][33]Many species live inunderground lakes,underground riversoraquifersand are popularly known ascavefish.[34] Fish range in size from the huge 16-metre (52ft)whale sharkto the tiny 8-millimetre (0.3in)stout infantfish. Fishspeciesdiversity is roughly divided equally between marine (oceanic) andfreshwaterecosystems.Coral reefsin theIndo-Pacificconstitute the center of diversity for marine fishes, whereas continental freshwater fishes are most diverse in largeriver basinsoftropical rainforests, especially theAmazon,Congo, andMekongbasins. More than 5,600 fish species inhabitNeotropicalfreshwaters alone, such thatNeotropical fishesrepresent about 10% of allvertebratespecies on the Earth. Exceptionally rich sites in the Amazon basin, such asCantão State Park, can contain more freshwater fish species than occur in all of Europe.[35] The deepest living fish in the ocean so far found is the Mariana snailfish (Pseudoliparis swirei) which lives at deeps of 8,000 meters (26,200 feet) along the Mariana Trench near Guam.[36] Thediversityof living fish (finfish) is unevenly distributed among the various groups, withteleostsmaking up the bulk of living fishes (96%), and over 50% of allvertebratespecies.[21]The followingcladogram[37]shows theevolutionary relationshipsof all groups of living fishes (with their respective diversity[21]) and the four-limbed vertebrates (tetrapods).  Diversityof various groups of fish (and othervertebrates) through time  Lungfishare the closest living relatives oftetrapods(four-limbed vertebrates).  ThebowfinAmia calvais the sole survivor of thehalecomorphclade. Vertebrates  Jawless fish(118 living species:hagfish,lampreys)  Jawedvertebrates  Cartilaginous fishes(>1,100 living species:sharks,rays,chimaeras)  Bonyfishes Lobe-finfishRhipidistia  Tetrapoda(>30,000 living species:amphibians,mammals,reptiles,birds)    Dipnoi(6 living species:lungfish)     Actinistia(2 living species:coelacanths)   Ray-finfish  Cladistia(14 living species:bichirs,reedfish)  Actinopteri  Chondrostei(27 living species:sturgeons,paddlefish)  Neopterygii Holostei  Ginglymodi(7 living species:gars,alligator gars)    Halecomorphi(1 living species:bowfin)     Teleostei(>32,000 living species)           Anatomy and physiology Further information:Fish anatomyandFish physiology  Organs: 1.Liver, 2.Gas bladder, 3.Roe, 4.Pyloric caeca, 5.Stomach, 6.Intestine Respiration See also:Aquatic respiration Gills  Tunagills inside the head. The fish head is oriented snout-downwards, with the view looking towards the mouth. Most fish exchange gases usinggillson either side of thepharynx. Gills consist of threadlike structures calledfilaments. Each filament contains acapillarynetwork that provides a largesurface areafor exchangingoxygenandcarbon dioxide. Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. In some fish, capillary blood flows in the opposite direction to the water, causingcountercurrent exchange. The gills push the oxygen-poor water out through openings in the sides of the pharynx. Some fish, likesharksandlampreys, possess multiple gill openings. However,bony fishhave a single gill opening on each side. This opening is hidden beneath a protective bony cover called anoperculum. Juvenilebichirshave external gills, a very primitive feature that they share with larvalamphibians. Air breathing Fish from multiple groups can live out of the water for extended periods.Amphibious fishsuch as themudskippercan live and move about on land for up to several days,[dubious–discuss]or live in stagnant or otherwise oxygen depleted water. Many such fish can breathe air via a variety of mechanisms. The skin ofanguillid eelsmay absorb oxygen directly. Thebuccal cavityof theelectric eelmay breathe air. Catfish of the familiesLoricariidae,Callichthyidae, andScoloplacidaeabsorb air through their digestive tracts.[38]Lungfish, with the exception of theAustralian lungfish, andbichirshave paired lungs similar to those oftetrapodsand must surface to gulp fresh air through the mouth and pass spent air out through the gills.Garandbowfinhave a vascularized swim bladder that functions in the same way.Loaches,trahiras, and manycatfishbreathe by passing air through the gut. Mudskippers breathe by absorbing oxygen across the skin (similar to frogs). A number of fish have evolved so-called accessory breathing organs that extract oxygen from the air. Labyrinth fish (such asgouramisandbettas) have alabyrinth organabove the gills that performs this function. A few other fish have structures resembling labyrinth organs in form and function, most notablysnakeheads,pikeheads, and theClariidaecatfish family. Breathing air is primarily of use to fish that inhabit shallow, seasonally variable waters where the water's oxygen concentration may seasonally decline. Fish dependent solely on dissolved oxygen, such as perch andcichlids, quickly suffocate, while air-breathers survive for much longer, in some cases in water that is little more than wet mud. At the most extreme, some air-breathing fish are able to survive in damp burrows for weeks without water, entering a state ofaestivation(summertime hibernation) until water returns. Air breathing fish can be divided into obligate air breathers and facultative air breathers. Obligate air breathers, such as theAfrican lungfish,mustbreathe air periodically or they suffocate. Facultative air breathers, such as the catfishHypostomus plecostomus, only breathe air if they need to and will otherwise rely on their gills for oxygen. Most air breathing fish are facultative air breathers that avoid the energetic cost of rising to the surface and the fitness cost of exposure to surface predators.[38] Circulation  Didactic modelof a fish heart Fish have aclosed-loop circulatory system. Theheartpumps the blood in a single loop throughout the body. In most fish, the heart consists of four parts, including two chambers and an entrance and exit.[39]The first part is thesinus venosus, a thin-walled sac that collects blood from the fish'sveinsbefore allowing it to flow to the second part, theatrium, which is a large muscular chamber. The atrium serves as a one-way antechamber, sends blood to the third part,ventricle. The ventricle is another thick-walled, muscular chamber and it pumps the blood, first to the fourth part,bulbus arteriosus, a large tube, and then out of the heart. The bulbus arteriosus connects to theaorta, through which blood flows to the gills for oxygenation. Digestion Jaws allow fish to eat a wide variety of food, including plants and other organisms. Fish ingest food through the mouth and break it down in theesophagus. In the stomach, food is further digested and, in many fish, processed in finger-shaped pouches calledpyloric caeca, which secrete digestiveenzymesand absorb nutrients. Organs such as theliverandpancreasadd enzymes and various chemicals as the food moves through the digestive tract. The intestine completes the process of digestion and nutrient absorption. Excretion As with many aquatic animals, most fish release their nitrogenous wastes asammonia. Some of the wastesdiffusethrough the gills. Blood wastes arefilteredby thekidneys. Saltwater fish tend to lose water because ofosmosis. Their kidneys return water to the body. The reverse happens infreshwater fish: they tend to gain water osmotically. Their kidneys produce dilute urine for excretion. Some fish have specially adapted kidneys that vary in function, allowing them to move from freshwater to saltwater. Scales Main article:Fish scale The scales of fish originate from themesoderm(skin); they may be similar in structure to teeth. Sensory and nervous system  Dorsal view of the brain of therainbow trout Central nervous system Fish typically have quite small brains relative to body size compared with other vertebrates, typically one-fifteenth the brain mass of a similarly sized bird or mammal.[40]However, some fish have relatively large brains, most notablymormyridsandsharks, which have brains about as massive relative to body weight as birds andmarsupials.[41] Fish brains are divided into several regions. At the front are theolfactory lobes, a pair of structures that receive and process signals from thenostrilsvia the twoolfactory nerves.[40]The olfactory lobes are very large in fish that hunt primarily by smell, such as hagfish, sharks, and catfish. Behind the olfactory lobes is the two-lobedtelencephalon, the structural equivalent to thecerebruminhigher vertebrates. In fish the telencephalon is concerned mostly witholfaction.[40]Together these structures form the forebrain. Connecting the forebrain to the midbrain is thediencephalon(in the diagram, this structure is below the optic lobes and consequently not visible). The diencephalon performs functions associated withhormonesandhomeostasis.[40]Thepineal bodylies just above the diencephalon. This structure detects light, maintainscircadianrhythms, and controls color changes.[40] Themidbrain(or mesencephalon) contains the twooptic lobes. These are very large in species that hunt by sight, such asrainbow troutandcichlids.[40] The hindbrain (ormetencephalon) is particularly involved in swimming and balance.[40]The cerebellum is a single-lobed structure that is typically the biggest part of the brain.[40]Hagfish andlampreyshave relatively small cerebellae, while themormyridcerebellum is massive and apparently involved in theirelectrical sense.[40] The brain stem (ormyelencephalon) is the brain's posterior.[40]As well as controlling some muscles and body organs, in bony fish at least, the brain stem governsrespirationandosmoregulation.[40] Sense organs Main article:Sensory systems in fish Most fish possess highly developed sense organs. Nearly all daylight fish have color vision that is at least as good as a human's (seevision in fishes). Many fish also have chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears, many fish may not hear very well. Most fish have sensitive receptors that form thelateral line system, which detects gentle currents and vibrations, and senses the motion of nearby fish and prey.[42]The sense information obtained from the lateral line system can be considered both a sense oftouchandhearing.Blind cave fishnavigate almost entirely through the sensations from their lateral line system.[43]Some fish, such as catfish and sharks, have theampullae of Lorenzini,electroreceptorsthat detect weak electric currents on the order of millivolt.[44]Other fish, like the South American electric fishesGymnotiformes, can produce weak electric currents, which they use in navigation and social communication. Fish orient themselves using landmarks and may use mental maps based on multiple landmarks or symbols. Fish behavior in mazes reveals that they possess spatial memory and visual discrimination.[45] Vision Main article:Vision in fishes Visionis an importantsensory systemfor most species of fish. Fish eyes are similar to those ofterrestrialvertebrateslikebirdsand mammals, but have a moresphericallens. Theirretinasgenerally have bothrodsandcones(forscotopicandphotopic vision), and most species havecolour vision. Some fish can seeultravioletand some can seepolarized light. Amongstjawless fish, thelampreyhas well-developed eyes, while thehagfishhas only primitiveeyespots.[46]Fish vision showsadaptationto their visual environment, for exampledeep sea fisheshave eyes suited to the dark environment. Hearing See also:Hearing in fish Hearingis an important sensory system for most species of fish. Fish sense sound using theirlateral linesand theirears. Cognition Further information:Fish intelligence New research has expanded preconceptions about the cognitive capacities of fish. For example,manta rayshave exhibited behavior linked toself-awarenessinmirror testcases. Placed in front of a mirror, individual rays engaged in contingency testing, that is, repetitive behavior aiming to check whether their reflection's behavior mimics their body movement.[47] Wrasseshave also passed the mirror test in a 2018 scientific study.[48][49] Cases of tool use have also been noticed, notably in theChoerodonfamily, inarcherfishandAtlantic cod.[50] Capacity for pain Further information:Pain in fish Experiments done by William Tavolga provide evidence that fish havepainand fear responses. For instance, in Tavolga's experiments,toadfishgrunted when electrically shocked and over time they came to grunt at the mere sight of an electrode.[51] In 2003, Scottish scientists at theUniversity of Edinburghand the Roslin Institute concluded that rainbow trout exhibit behaviors often associated withpainin other animals.Beevenomandacetic acidinjected into the lips resulted in fish rocking their bodies and rubbing their lips along the sides and floors of their tanks, which the researchers concluded were attempts to relieve pain, similar to what mammals would do.[52][53]Neurons fired in a pattern resembling human neuronal patterns.[53] Professor James D. Rose of theUniversity of Wyomingclaimed the study was flawed since it did not provide proof that fish possess "conscious awareness, particularly a kind of awareness that is meaningfully like ours".[54]Rose argues that since fish brains are so different from human brains, fish are probably not conscious in the manner humans are, so that reactions similar to human reactions to pain instead have other causes. Rose had published a study a year earlier arguing that fish cannot feel pain because their brains lack aneocortex.[55]However, animal behavioristTemple Grandinargues that fish could still have consciousness without a neocortex because "different species can use different brain structures and systems to handle the same functions."[53] Animal welfare advocates raise concerns about the possiblesufferingof fish caused by angling. Some countries, such as Germany, have banned specific types of fishing, and the BritishRSPCAnow formally prosecutes individuals who are cruel to fish.[56] Emotion In 2019, scientists have shown that members of themonogamousspeciesAmatitlania siquiaexhibit pessimistic behavior when they are prevented from being with their partner.[57] Muscular system Main article:Fish locomotion  The anatomy ofLampanyctodes hectoris(1)operculum (gill cover), (2)lateral line, (3)dorsal fin, (4)fat fin, (5)caudal peduncle, (6)caudal fin, (7)anal fin, (8)photophores, (9)pelvic fins (paired), (10)pectoral fins (paired)  Swim bladder of a rudd (Scardinius erythrophthalmus) Most fish move by alternately contracting paired sets of muscles on either side of the backbone. These contractions form S-shaped curves that move down the body. As each curve reaches the back fin, backward force is applied to the water, and in conjunction with the fins, moves the fish forward. The fish's fins function like an airplane's flaps. Fins also increase the tail's surface area, increasing speed. The streamlined body of the fish decreases the amount of friction from the water. Since body tissue is denser than water, fish must compensate for the difference or they will sink. Many bony fish have an internal organ called aswim bladderthat adjusts their buoyancy through manipulation of gases. Endothermy Although most fish are exclusivelyectothermic, there are exceptions. The only known bony fishes (infraclassTeleostei) that exhibitendothermyare in the suborderScombroidei– which includes thebillfishes, tunas, and thebutterfly kingfish, abasalspecies of mackerel[58]– and also theopah. The opah, alampriform, was demonstrated in 2015 to utilize "whole-body endothermy", generating heat with its swimming muscles to warm its body while countercurrent exchange (as in respiration) minimizes heat loss.[59]It is able to actively hunt prey such as squid and swim for long distances due to the ability to warm its entire body, including its heart,[60]which is a trait typically found in only mammals and birds (in the form ofhomeothermy). In the cartilaginous fishes (classChondrichthyes), sharks of the familiesLamnidae(porbeagle, mackerel, salmon, and great white sharks) andAlopiidae(thresher sharks) exhibit endothermy. The degree of endothermy varies from the billfishes, which warm only their eyes and brain, to thebluefin tunaand theporbeagle shark, which maintain body temperatures in excess of 20°C (68°F) above ambient water temperatures.[58] Endothermy, though metabolically costly, is thought to provide advantages such as increased muscle strength, higher rates of centralnervous systemprocessing, and higher rates ofdigestion. Reproductive system Further information:Fish reproductionandSpawn (biology)  Ovary of fish (Corumbatá) Fish reproductive organs includetesticlesandovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused.[61]There may also be a range of secondary organs that increase reproductive fitness. In terms ofspermatogoniadistribution, the structure ofteleoststestes has two types: in the most common, spermatogonia occur all along theseminiferous tubules, while inatherinomorphfish they are confined to thedistalportion of these structures. Fish can present cystic or semi-cysticspermatogenesisin relation to the release phase of germ cells in cysts to the seminiferous tubuleslumen.[61] Fish ovaries may be of three types: gymnovarian, secondary gymnovarian or cystovarian. In the first type, theoocytesare released directly into thecoelomiccavity and then enter theostium, then through theoviductand are eliminated. Secondary gymnovarian ovaries shedovainto the coelom from which they go directly into the oviduct. In the third type, the oocytes are conveyed to the exterior through the oviduct.[62]Gymnovaries are the primitive condition found inlungfish,sturgeon, andbowfin. Cystovaries characterize most teleosts, where the ovary lumen has continuity with the oviduct.[61]Secondary gymnovaries are found insalmonidsand a few other teleosts. Oogoniadevelopment in teleosts fish varies according to the group, and the determination of oogenesis dynamics allows the understanding of maturation and fertilization processes. Changes in thenucleus, ooplasm, and the surrounding layers characterize the oocyte maturation process.[61] Postovulatoryfolliclesare structures formed after oocyte release; they do not haveendocrinefunction, present a wide irregular lumen, and are rapidly reabsorbed in a process involving theapoptosisof follicular cells. A degenerative process calledfollicular atresiareabsorbs vitellogenic oocytes not spawned. This process can also occur, but less frequently, in oocytes in other development stages.[61] Some fish, like theCalifornia sheephead, arehermaphrodites, having both testes and ovaries either at different phases in their life cycle or, as inhamlets, have them simultaneously. Over 97% of all known fish areoviparous,[63]that is, the eggs develop outside the mother's body. Examples of oviparous fish includesalmon,goldfish,cichlids,tuna, andeels. In the majority of these species, fertilisation takes place outside the mother's body, with the male and female fish shedding theirgametesinto the surrounding water. However, a few oviparous fish practice internal fertilization, with the male using some sort ofintromittent organto deliver sperm into the genital opening of the female, most notably the oviparous sharks, such as thehorn shark, and oviparous rays, such asskates. In these cases, the male is equipped with a pair of modifiedpelvic finsknown asclaspers. Marine fish can produce high numbers of eggs which are often released into the open water column. The eggs have an average diameter of 1 millimetre (0.04in).  Egg oflamprey  Egg ofcatshark(mermaids' purse)  Egg ofbullhead shark  Egg ofchimaera The newly hatched young of oviparous fish are calledlarvae. They are usually poorly formed, carry a largeyolk sac(for nourishment), and are very different in appearance from juvenile and adult specimens. The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termedmetamorphosis) to become juveniles. During this transition larvae must switch from their yolk sac to feeding onzooplanktonprey, a process which depends on typically inadequate zooplankton density, starving many larvae. Inovoviviparousfish the eggs develop inside the mother's body after internal fertilization but receive little or no nourishment directly from the mother, depending instead on theyolk. Each embryo develops in its own egg. Familiar examples of ovoviviparous fish includeguppies,angel sharks, andcoelacanths. Some species of fish areviviparous. In such species the mother retains the eggs and nourishes the embryos. Typically, viviparous fish have a structure analogous to theplacentaseen inmammalsconnecting the mother's blood supply with that of the embryo. Examples of viviparous fish include thesurf-perches,splitfins, andlemon shark. Some viviparous fish exhibitoophagy, in which the developing embryos eat other eggs produced by the mother. This has been observed primarily among sharks, such as theshortfin makoandporbeagle, but is known for a few bony fish as well, such as thehalfbeakNomorhamphus ebrardtii.[64]Intrauterine cannibalismis an even more unusual mode of vivipary, in which the largest embryos eat weaker and smaller siblings. This behavior is also most commonly found among sharks, such as thegrey nurse shark, but has also been reported forNomorhamphus ebrardtii.[64] Aquaristscommonly refer to ovoviviparous and viviparous fish aslivebearers. Acoustic communication See also:Acoustic communication in aquatic animals Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another. The production of sounds as a means of communication among fish is most often used in the context of feeding, aggression or courtship behaviour.[3]The sounds emitted can vary depending on the species and stimulus involved. Fish can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder.[65] Stridulatory  French grunts –Haemulon flavolineatum There are some species of fish that can produce sounds by rubbing or grinding their bones together. These noises produced by bone-on-bone interactions are known as 'stridulatory sounds'.[65] An example of this is seen inHaemulon flavolineatum, a species commonly referred to as the 'French grunt fish', as it produces a grunting noise by grinding its teeth together.[65]This behaviour is most pronounced when theH. flavolineatumis in distress situations.[65]The grunts produced by this species of fishes generate a frequency of approximately 700Hz, and last approximately 47 milliseconds.[65]TheH. flavolineatumdoes not emit sounds with frequencies greater than 1000Hz, and does not detect sounds that have frequencies greater than 1050Hz.[65] In a study conducted by Oliveira et al. (2014), the longsnout seahorse,Hippocampus reidi, was recorded producing two different categories of sounds; 'clicks' and 'growls'. The sounds emitted by theH. reidiare accomplished by rubbing their coronet bone across the grooved section of their neurocranium.[66]'Clicking' sounds were found to be primarily produced during courtship and feeding, and the frequencies of clicks were within the range of 50Hz-800Hz.[67]The frequencies were noted to be on the higher end of the range during spawning periods, when the female and male fishes were less than fifteen centimeters apart.[67]Growl sounds were produced when theH. reidiencountered stressful situations, such as handling by researchers.[67]The 'growl' sounds consist of a series of sound pulses and are emitted simultaneously with body vibrations.[67] Non-stridulatory  Oyster toadfish Some fish species create noise by engaging specialized muscles that contract and cause swimbladder vibrations. Oyster toadfishproduce loud grunting sounds by contracting muscles located along the sides of their swim bladder, known as sonic muscles[68]Female and male toadfishes emit short-duration grunts, often as a fright response.[69]In addition to short-duration grunts, male toadfishes produce "boat whistle calls".[70]These calls are longer in duration, lower in frequency, and are primarily used to attract mates.[70]The sounds emitted by theO. taohave frequency range of 140Hz to 260Hz.[70]The frequencies of the calls depend on the rate at which the sonic muscles contract.[71][68] The red drum,Sciaenops ocellatus, produces drumming sounds by vibrating its swimbladder.[72]Vibrations are caused by the rapid contraction of sonic muscles that surround the dorsal aspect of the swimbladder.[72]These vibrations result in repeated sounds with frequencies that range from 100 to >200Hz.[72]TheS. ocellatuscan produce different calls depending on the stimuli involved.[72]The sounds created in courtship situations are different from those made during distressing events such as predatorial attacks.[72]Unlike the males of theS. ocellatusspecies, the females of this species do not produce sounds and lack sound-producing (sonic) muscles.[72] Diseases Main article:Fish diseases and parasites Like other animals, fish suffer from diseases and parasites. To prevent disease they have a variety of defenses.Non-specificdefenses include the skin and scales, as well as the mucus layer secreted by theepidermisthat traps and inhibits the growth ofmicroorganisms. Ifpathogensbreach these defenses, fish can develop aninflammatory responsethat increases blood flow to the infected region and deliverswhite blood cellsthat attempt to destroy pathogens. Specific defenses respond to particular pathogens recognised by the fish's body, i.e., animmune response.[73]In recent years,vaccineshave become widely used in aquaculture and also with ornamental fish, for examplefurunculosisvaccines in farmedsalmonandkoi herpes virusinkoi.[74][75] Some species usecleaner fishto remove external parasites. The best known of these are thebluestreak cleaner wrassesof the genusLabroidesfound oncoral reefsin theIndianandPacificoceans. These small fish maintain so-called "cleaning stations" where other fish congregate and perform specific movements to attract the attention of the cleaners.[76]Cleaning behaviors have been observed in a number of fish groups, including an interesting case between two cichlids of the same genus,Etroplus maculatus, the cleaner, and the much largerEtroplus suratensis.[77] Immune system Immune organs vary by type of fish.[78]In thejawless fish(lampreys and hagfish), truelymphoidorgans are absent. These fish rely on regions oflymphoid tissuewithin other organs to produce immune cells. For example,erythrocytes,macrophagesandplasma cellsare produced in the anterior kidney (orpronephros) and some areas of the gut (wheregranulocytesmature.) They resemble primitivebone marrowin hagfish.Cartilaginous fish(sharks and rays) have a more advanced immune system. They have three specialized organs that are unique toChondrichthyes; the epigonal organs (lymphoid tissue similar to mammalian bone) that surround the gonads, theLeydig's organwithin the walls of their esophagus, and aspiral valvein their intestine. These organs house typical immune cells (granulocytes, lymphocytes and plasma cells). They also possess an identifiablethymusand a well-developedspleen(their most important immune organ) where variouslymphocytes, plasma cells and macrophages develop and are stored.Chondrosteanfish (sturgeons, paddlefish, and bichirs) possess a major site for the production of granulocytes within a mass that is associated with themeninges(membranes surrounding the central nervous system.) Their heart is frequently covered with tissue that contains lymphocytes,reticular cellsand a small number ofmacrophages. The chondrostean kidney is an importanthemopoieticorgan; where erythrocytes, granulocytes, lymphocytes and macrophages develop. Like chondrostean fish, the major immune tissues of bony fish (orteleostei) include the kidney (especially the anterior kidney), which houses many different immune cells.[79]In addition, teleost fish possess a thymus, spleen and scattered immune areas within mucosal tissues (e.g. in the skin, gills, gut and gonads). Much like the mammalian immune system, teleost erythrocytes, neutrophils and granulocytes are believed to reside in the spleen whereas lymphocytes are the major cell type found in the thymus.[80][81]In 2006, a lymphatic system similar to that in mammals was described in one species of teleost fish, thezebrafish. Although not confirmed as yet, this system presumably will be where naive (unstimulated)T cellsaccumulate while waiting to encounter anantigen.[82] B and T lymphocytes bearingimmunoglobulinsandT cell receptors, respectively, are found in all jawed fishes. Indeed, theadaptive immune systemas a wholeevolvedin an ancestor of all jawed vertebrates.[83] Conservation The 2006IUCNRed Listnames 1,173 fish species that are threatened with extinction.[84]Included are species such asAtlantic cod,[85]Devil's Hole pupfish,[86]coelacanths,[87]andgreat white sharks.[88]Because fish live underwater they are more difficult to study than terrestrial animals and plants, and information about fish populations is often lacking. However, freshwater fish seem particularly threatened because they often live in relatively small water bodies. For example, theDevil's Hole pupfishoccupies only a single 3 by 6 metres (10 by 20ft) pool.[89] Overfishing  Whale sharks, the largest species of fish, are classified asvulnerable. Main article:Overfishing Overfishing is a major threat to edible fish such as cod andtuna.[90][91]Overfishing eventually causespopulation(known asstock) collapse because the survivors cannot produce enough young to replace those removed. Suchcommercial extinctiondoes not mean that the species is extinct, merely that it can no longer sustain a fishery. One well-studied example of fishery collapse is thePacific sardineSadinops sagax caeruluesfishery off the California coast. From a 1937 peak of 790,000 long tons (800,000t) the catch steadily declined to only 24,000 long tons (24,000t) in 1968, after which the fishery was no longer economically viable.[92] The main tension betweenfisheries scienceand thefishing industryis that the two groups have different views on the resiliency of fisheries to intensive fishing. In places such as Scotland, Newfoundland, and Alaska the fishing industry is a major employer, so governments are predisposed to support it.[93][94]On the other hand, scientists and conservationists push for stringent protection, warning that many stocks could be wiped out within fifty years.[95][96] Habitat destruction See also:Environmental impact of fishing A key stress on both freshwater and marine ecosystems is habitat degradation includingwater pollution, the building of dams, removal of water for use by humans, and the introduction ofexoticspecies.[97]An example of a fish that has become endangered because of habitat change is thepallid sturgeon, a North American freshwater fish that lives in rivers damaged by human activity.[98] Exotic species Introduction ofnon-nativespecies has occurred in many habitats. One of the best studied examples is the introduction ofNile perchintoLake Victoriain the 1960s. Nile perch gradually exterminated the lake's 500endemiccichlidspecies. Some of them survive now in captive breeding programmes, but others are probably extinct.[99]Carp,snakeheads,[100]tilapia,European perch,brown trout,rainbow trout, andsea lampreysare other examples of fish that have caused problems by being introduced into alien environments. Importance to humans Economic Main articles:Fishing industry,Aquaculture, andFish farming  These fish-farming ponds were created as acooperativeproject in a rural village. Throughout history, humans have utilizedfish as a food source. Historically and today, most fishproteinhas come by means of catching wild fish. However, aquaculture, or fish farming, which has been practiced since about 3,500 BCE. in China,[101]is becoming increasingly important in many nations. Overall, about one-sixth of the world's protein is estimated to be provided by fish.[102]That proportion is considerably elevated in somedeveloping nationsand regions heavily dependent on the sea. In a similar manner, fish have been tied to trade.  Fish counter display at theOulu Market HallinOulu, Finland. Catching fish for the purpose of food or sport is known asfishing, while the organized effort by humans to catch fish is called afishery. Fisheries are a huge global business and provide income for millions of people.[102]The annual yield from all fisheries worldwide is about 154 million tons,[103]with popular species includingherring,cod,anchovy,tuna,flounder, andsalmon. However, the term fishery is broadly applied, and includes more organisms than just fish, such asmollusksandcrustaceans, which are often called "fish" when used as food. Recreation  ABengalifish vendor Main articles:Fishkeeping,Recreational fishing, andAngling Fishkeeping Fish have been recognized as a source of beauty for almost as long as used for food, appearing incave art, being raised asornamental fishin ponds, and displayed inaquariumsin homes, offices, or public settings. Recreational fishing Recreational fishingis fishing primarily for pleasure or competition; it can be contrasted withcommercial fishing, which is fishing for profit, orartisanal fishing, which is fishing primarily for food. The most common form of recreational fishing is done with arod,reel,line,hooks, and any one of a wide range ofbaits. Recreational fishing is particularly popular in North America and Europe and state, provincial, and federal government agencies actively management target fish species.[104][105]Angling is a method of fishing, specifically the practice of catching fish by means of an "angle" (hook). Anglers must select the right hook,castaccurately, and retrieve at the right speed while considering water and weather conditions, species, fish response, time of the day, and other factors. Culture Main article:Fish in culture  AvatarofVishnuas aMatsya Fish themes have symbolic significance in many religions. In ancientMesopotamia, fish offerings were made to the gods from the very earliest times.[106]Fish were also a major symbol ofEnki, the god of water.[106]Fish frequently appear as filling motifs incylinder sealsfrom theOld Babylonian(c.1830 BC –c.1531 BC) andNeo-Assyrian(911–609 BC) periods.[106]Starting during theKassite Period(c.1600 BC –c.1155 BC) and lasting until the earlyPersian Period(550–30 BC), healers and exorcists dressed in ritual garb resembling the bodies of fish.[106]During theSeleucid Period(312–63 BC), the legendary Babylonianculture heroOannes, described byBerossus, was said to have dressed in the skin of a fish.[106]Fish were sacred to the Syrian goddessAtargatis[107]and, during her festivals, only her priests were permitted to eat them.[107]  Theichthusis a Christian symbol of a fish signifying that the person who uses it is a Christian.[107][108] In theBook of Jonah, a work of Jewish literature probably written in the fourth century BC, the central figure, aprophetnamedJonah, is swallowed by a giant fish after being thrown overboard by the crew of the ship he is travelling on.[109][110][111]The fish later vomits Jonah out on shore after three days.[109][110][111]This book was later included as part of theHebrew Bible, or ChristianOld Testament,[112][113]and a version of the story it contains is summarized inSurah37:139-148 of theQuran.[114]Early Christiansused theichthys, a symbol of a fish, to represent Jesus,[107][108]because the Greek word for fish, ΙΧΘΥΣ Ichthys, could be used as an acronym for "Ίησοῦς Χριστός, Θεοῦ Υἱός, Σωτήρ" (Iesous Christos, Theou Huios, Soter), meaning "Jesus Christ, Son of God, Saviour".[107][108]Thegospelsalso refer to "fishers of men"[115]andfeeding the multitude. In thedhammaofBuddhism, the fish symbolize happiness as they have complete freedom of movement in the water. Often drawn in the form ofcarpwhich are regarded in the Orient as sacred on account of their elegant beauty, size and life-span. Among thedeitiessaid to take the form of a fish areIka-Roaof thePolynesians,Dagonof various ancientSemitic peoples, the shark-gods ofHawaiʻiandMatsyaof the Hindus. TheastrologicalsymbolPiscesis based on a constellation of thesame name, but there is also a second fish constellation in the night sky,Piscis Austrinus.[116] Fish feature prominently in art and literature, in movies such asFinding Nemoand books such asThe Old Man and the Sea. Large fish, particularly sharks, have frequently been the subject ofhorror moviesandthrillers, most notably the novelJaws, which spawned a series of films of thesame namethat in turn inspired similar films or parodies such asShark TaleandSnakehead Terror. Piranhas are shown in a similar light to sharks in films such asPiranha; however, contrary to popular belief, thered-bellied piranhais actually a generally timid scavenger species that is unlikely to harm humans.[117]Legends of half-human, half-fishmermaidshave featured in folklore, including the stories ofHans Christian Andersen. Terminology "Fish" or "fishes" Though often used interchangeably, in biology these words have different meanings.Fishis used as a singular noun, or as a plural to describe multiple individuals from a single species.Fishesis used to describe different species or species groups.[118][119][120]Thus a pond would be said to contain 120 fish if all were from a single species or 120 fishes if these included a mix of several species. The distinction is similar to that between people and peoples. "True fish" or "finfish" In biology, the termfishis most strictly used to describe any animal with abackbone,gillsthroughout life, and limbs (if any) in the shape offins.[23]Many types ofaquatic animalswith common names ending in "fish" are not fish in thissense; examples includeshellfish,cuttlefish,starfish,crayfishandjellyfish. In earlier times, even biologists did not make a distinction– sixteenth century natural historians classified alsoseals, whales,amphibians,crocodiles, evenhippopotamuses, as well as a host of aquatic invertebrates, as fish.[26] In fisheries, the termfishis used as a collective term, and includesmollusks,crustaceansand anyaquatic animalwhich is harvested.[121] The strict biological definition of a fish, above, is sometimes called atrue fish. True fish are also referred to asfinfishorfin fishto distinguish them from other aquatic life harvested in fisheries or aquaculture. "Shoal" or "school" Main article:Shoaling and schooling  Thesegoldband fusiliersareschoolingbecause their swimming is synchronised. An assemblage of fish merely using some localised resource such as food or nesting sites is known simply as anaggregation. When fish come together in an interactive, social grouping, then they may be forming either ashoalor aschooldepending on the degree of organisation. Ashoalis a loosely organised group where each fish swims and forages independently but is attracted to other members of the group and adjusts its behaviour, such as swimming speed, so that it remains close to the other members of the group.Schoolsof fish are much more tightly organised, synchronising their swimming so that all fish move at the same speed and in the same direction. Shoaling and schooling behaviour is believed to provide a variety of advantages.[122] Examples: Cichlids congregating atlekkingsites form anaggregation. Many minnows and characins formshoals. Anchovies, herrings and silversides are classic examples ofschoolingfish. The most common collective nouns for a group of fish in general are school and shoal. Both the words have evolved from the same common Dutch root 'schole' meaning a troop or crowd. While the words "school" and "shoal" have different meanings within biology, the distinctions are often ignored by non-specialists who treat the words assynonyms. Thus speakers ofBritish Englishcommonly use "shoal" to describe any grouping of fish, and speakers ofAmerican Englishcommonly use "school" just as loosely.[123]

Turtles are an order of reptiles known as Testudines, characterized by a shell developed mainly from their ribs. Modern turtles are divided into two major groups, the side-necked turtles and hidden neck turtles, which differ in the way the head retracts. There are 360 living and recently extinct species of turtles, including land-dwelling tortoises and freshwater terrapins. They are found on most continents, some islands and, in the case of sea turtles, much of the ocean. Like other reptiles, birds, and mammals, they breathe air and do not lay eggs underwater, although many species live in or around water. Genetic evidence typically places them in close relation to crocodilians and birds. Turtles Temporal range: Late Jurassic – Present PreꞒꞒOSDCPTJKPgN Turtle diversity.jpg Turtles from different families; clockwise from top-left: Red-bellied short-necked turtle, Indian flapshell turtle, Hawksbill sea turtle, and Galápagos tortoise Scientific classificatione Kingdom: Animalia Phylum: Chordata Class: Reptilia Clade: Pantestudines Clade: Testudinata Clade: Perichelydia Order: Testudines Batsch, 1788[1] Subgroups Cryptodira Pleurodira †Paracryptodira Diversity 14 living families World.distribution.testudines.1.png Blue: sea turtles, black: land turtles Synonyms[2] Chelonii Latreille 1800 Chelonia Ross and Macartney 1802 Turtle shells are made mostly of bone; the upper part is the domed carapace, while the underside is the flatter plastron or belly-plate. Its outer surface is covered in scales made of keratin, the material of hair, horns, and claws. The carapace bones develop from ribs that grow sideways and develop into broad flat plates that join up to cover the body. Turtles are ectotherms or "cold-blooded", meaning that their internal temperature varies with their direct environment. They are generally opportunistic omnivores and mainly feed on plants and animals with limited movements. Many turtles migrate short distances seasonally. Sea turtles are the only reptiles that migrate long distances to lay their eggs on a favored beach. Turtles have appeared in myths and folktales around the world. Some terrestrial and freshwater species are widely kept as pets. Turtles have been hunted for their meat, for use in traditional medicine, and for their shells. Sea turtles are often killed accidentally as bycatch in fishing nets. Turtle habitats around the world are being destroyed. As a result of these pressures, many species are threatened with extinction. Contents Naming and etymology The word turtle is derived from the French tortue or tortre ('turtle, tortoise').[3] It is a common name and may be used without knowledge of taxonomic distinctions. In North America, it may denote the order as a whole. In Britain, the name is used for sea turtles as opposed to freshwater terrapins and land-dwelling tortoises. In Australia, which lacks true tortoises (family Testudinidae), non-marine turtles were traditionally called tortoises, but more recently turtle has been used for the entire group.[4] The name of the order, Testudines (/tɛˈstjuːdɪniːz/ teh-STEW-din-eez), is based on the Latin word for tortoise, testudo;[5] and was coined by German naturalist August Batsch in 1788.[1] The order has also been historically known as Chelonii (Latreille 1800) and Chelonia (Ross and Macartney 1802),[2] which are based on the Ancient Greek word for tortoise: χελώνη (chelone).[6][7] Testudines is the official order name due to the principle of priority.[2] The term chelonian is used as a formal name for members of the group.[1][8] Anatomy and physiology Size The largest living species of turtle (and fourth-largest reptile) is the leatherback turtle, which can reach over 2.7 m (8 ft 10 in) in length and weigh over 500 kg (1,100 lb).[9] The largest known turtle was Archelon ischyros, a Late Cretaceous sea turtle up to 4.5 m (15 ft) long, 5.25 m (17 ft) wide between the tips of the front flippers, and estimated to have weighed over 2,200 kg (4,900 lb).[10] The smallest living turtle is Chersobius signatus of South Africa, measuring no more than 10 cm (3.9 in) in length[11] and weighing 172 g (6.1 oz).[12] Shell Main article: Turtle shell Photograph of one half of a tortoise skeleton, cut in half vertically showing the vertebrae following curving along the carapace Sagittal section of a tortoise skeleton The shell of a turtle is unique among vertebrates and serves to protect the animal and provide shelter from the elements.[13][14][15] It is primarily made of 50–60 bones and consists of two parts: the domed, dorsal (back) carapace and the flatter, ventral (belly) plastron. They are connected by lateral (side) extensions of the plastron.[13][16] The carapace is fused with the vertebrae and ribs while the plastron is formed from bones of the shoulder girdle, sternum, and gastralia (abdominal ribs).[13] During development, the ribs grow sideways into a carapacial ridge, unique to turtles, entering the dermis (inner skin) of the back to support the carapace. The development is signaled locally by proteins known as fibroblast growth factors that include FGF10.[17] The shoulder girdle in turtles is made up of two bones, the scapula and the coracoid.[18] Both the shoulder and pelvic girdles of turtles are located within the shell and hence are effectively within the rib cage. The trunk ribs grow over the shoulder girdle during development.[19] Drawing of a section through a turtle embryo showing formation of the shell, with the ribs growing sideways Development of the shell. The ribs are growing sideways into the carapacial ridge, seen here as a bud, to support the carapace.[17] The shell is covered in epidermal (outer skin) scales known as scutes that are made of keratin, the same substance that makes up hair and fingernails. Typically, a turtle has 38 scutes on the carapace and 16 on the plastron, giving them 54 in total. Carapace scutes are divided into "marginals" around the margin and "vertebrals" over the vertebral column, though the scute that overlays the neck is called the "cervical". "Pleurals" are present between the marginals and vertebrals.[20] Plastron scutes include gulars (throat), humerals, pectorals, abdominals, and anals. Side-necked turtles additionally have "intergular" scutes between the gulars.[16][21] Turtle scutes are usually structured like mosaic tiles, but some species, like the hawksbill sea turtle, have overlapping scutes on the carapace.[16] The shapes of turtle shells vary with the adaptations of the individual species, and sometimes with sex. Land-dwelling turtles are more dome-shaped, which appears to make them more resistant to being crushed by large animals. Aquatic turtles have flatter, smoother shells that allow them to cut through the water. Sea turtles in particular have streamlined shells that reduce drag and increase stability in the open ocean. Some turtle species have pointy or spiked shells that provide extra protection from predators and camouflage against the leafy ground. The lumps of a tortoise shell can tilt its body when it gets flipped over, allowing it to flip back. In male tortoises, the tip of the plastron is thickened and used for butting and ramming during combat.[22] Shells vary in flexibility. Some species, such as box turtles, lack the lateral extensions and instead have the carapace bones fully fused or ankylosed together. Several species have hinges on their shells, usually on the plastron, which allow them to expand and contract. Softshell turtles have rubbery edges, due to the loss of bones. The leatherback turtle has hardly any bones in its shell, but has thick connective tissue and an outer layer of leathery skin.[23] Head and neck Head and neck of a European pond turtle The turtle's skull is unique among living amniotes (which includes reptiles, birds and mammals), it is solid and rigid with no openings for muscle attachment (temporal fenestrae).[24][25] Muscles instead attach to recesses in the back of the skull. Turtle skulls vary in shape, from the long and narrow skulls of softshells to the broad and flattened skull of the mata mata.[25] Some turtle species have developed large and thick heads, allowing for greater muscle mass and stronger bites.[26] Turtles that are carnivorous or durophagous (eating hard-shelled animals) have the most powerful bites. For example, the durophagous Mesoclemmys nasuta has a bite force of 432 N. Species that are insectivorous, piscivorous (fish-eating), or omnivorous have lower bite forces.[27] Living turtles lack teeth but have beaks made of keratin sheaths along the edges of the jaws.[28][13] These sheaths may have sharp edges for cutting meat, serrations for clipping plants, or broad plates for breaking mollusks.[29] The necks of turtles are highly flexible, possibly to compensate for their rigid shells. Some species, like sea turtles, have short necks while others, such as snake-necked turtles, have long ones. Despite this, all turtle species have eight neck vertebrae, a consistency not found in other reptiles but similar to mammals.[30] Some snake-necked turtles have both long necks and large heads, limiting their ability to lift them when not in water.[26] Some turtles have folded structures in the larynx or glottis that vibrate to produce sound. Other species have elastin-rich vocal cords.[31][32] Limbs and locomotion Due to their heavy shells, turtles are slow-moving on land. A desert tortoise moves at only 0.22–0.48 km/h (0.14–0.30 mph). By contrast, sea turtles can swim at 30 km/h (19 mph).[13] The limbs of turtles are adapted for various means of locomotion and habits and most have five toes. Tortoises are specialized for terrestrial environments and have column-like legs with elephant-like feet and short toes. The gopher tortoise has flattened front limbs for digging in the substrate. Freshwater turtles have more flexible legs and longer toes with webbing, giving them thrust in the water. Some of these species, such as snapping turtles and mud turtles, mainly walk along the water bottom, as they would on land. Others, such as terrapins, swim by paddling with all four limbs, switching between the opposing front and hind limbs, which keeps their direction stable.[13][33] Sea turtles have streamlined shells and limbs adapted for fast and efficient swimming.[34] Sea turtles and the pig-nosed turtle are the most specialized for swimming. Their front limbs have evolved into flippers while the shorter hind limbs are shaped more like rudders. The front limbs provide most of the thrust for swimming, while the hind limbs serve as stabilizers.[13][35] Sea turtles such as the green sea turtle rotate the front limb flippers like a bird's wings to generate a propulsive force on both the upstroke and on the downstroke. This is in contrast to similar-sized freshwater turtles (measurements having been made on young animals in each case) such as the Caspian turtle, which uses the front limbs like the oars of a rowing boat, creating substantial negative thrust on the recovery stroke in each cycle. In addition, the streamlining of the marine turtles reduces drag. As a result, marine turtles produce a propulsive force twice as large, and swim six times as fast, as freshwater turtles. The swimming efficiency of young marine turtles is similar to that of fast-swimming fish of open water, like mackerel.[34] Compared to other reptiles, turtles tend to have reduced tails, but these vary in both length and thickness among species and between sexes. Snapping turtles and the big-headed turtle have longer tails; the latter uses it for balance while climbing. The cloaca is found underneath and at the base, and the tail itself houses the reproductive organs. Hence, males have longer tails to contain the penis. In sea turtles, the tail is longer and more prehensile in males, who use it to grasp mates. Several turtle species have spines on their tails.[36][24] Senses The red-eared slider has an exceptional seven types of color-detecting cells in its eyes.[37] Turtles make use of vision to find food and mates, avoid predators, and orient themselves. The retina's light-sensitive cells include both rods for vision in low light, and cones with three different photopigments for bright light, where they have full-color vision. There is possibly a fourth type of cone that detects ultraviolet, as hatchling sea turtles respond experimentally to ultraviolet light, but it is unknown if they can distinguish this from longer wavelengths. A freshwater turtle, the red-eared slider, has an exceptional seven types of cone cell.[37][38][39] Sea turtles orient themselves on land by night, using visual features detected in dim light. They can use their eyes in clear surface water, muddy coasts, the darkness of the deep ocean, and also above water. Unlike in terrestrial turtles, the cornea, the curved surface that lets light into the eye, does not help to focus light on the retina, so focusing underwater is handled entirely by the lens, behind the cornea. The cone cells contain oil droplets placed to shift perception toward the red part of the spectrum, improving color discrimination. Visual acuity, studied in hatchlings, is highest in a horizontal band with retinal cells packed about twice as densely as elsewhere. This gives the best vision along the visual horizon. Sea turtles do not appear to use polarized light for orientation as many other animals do. The deep-diving leatherback turtle lacks specific adaptations to low light, such as large eyes, large lenses, or a reflective tapetum. It may rely on seeing the bioluminescence of prey when hunting in deep water.[37] Turtles have no ear openings; the eardrum is covered with scales and encircled by a bony otic capsule, which is absent in other reptiles.[30] Their hearing thresholds are high in comparison to other reptiles, reaching up to 500 Hz in air, but underwater they are more attuned to lower frequencies.[40] The loggerhead sea turtle has been shown experimentally to respond to low sounds, with maximal sensitivity between 100 and 400 Hz.[41] Turtles have olfactory (smell) and vomeronasal receptors along the nasal cavity, the latter of which are used to detect chemical signals.[42] Experiments on green sea turtles showed they could learn to respond to a selection of different odorant chemicals such as triethylamine and cinnamaldehyde, which were detected by olfaction in the nose. Such signals could be used in navigation.[43] Breathing A submerged Indian softshell turtle nose-breathing at river surface The rigid shell of turtles is not capable of expanding and making room for the lungs, as in other amniotes, so they have had to evolve special adaptations for respiration.[44][45][46] The lungs of turtles are attached directly to the carapace above while below, connective tissue attaches them to the organs.[47] They have multiple lateral (side) and medial (middle) chambers (the numbers of which vary between species) and one terminal (end) chamber.[48] The lungs are ventilated using specific groups of abdominal muscles attached to the organs that pull and push on them.[44] Specifically, it is the turtle's large liver that compresses the lungs. Underneath the lungs, in the coelomic cavity, the liver is connected to the right lung by the root, and the stomach is directly attached to the left lung, and to the liver by a mesentery. When the liver is pulled down, inhalation begins.[45] Supporting the lungs is a wall or septum, which is thought to prevent them from collapsing.[49] During exhalation, the contraction of the transversus abdominis muscle propels the organs into the lungs and expels air. Conversely, during inhalation, the relaxing and flattening of the oblique abdominis muscle pulls the transversus back down, allowing air back into the lungs.[45] Although many turtles spend large amounts of their lives underwater, all turtles breathe air and must surface at regular intervals to refill their lungs. Depending on the species, immersion periods vary between a minute and an hour.[50] Some species can respire through the cloaca, which contains large sacs that are lined with many finger-like projections that take up dissolved oxygen from the water.[51] Circulation Snapping turtle emerging from period of brumation, in which it buried itself in mud. Turtles have multiple circulatory and physiological adaptations to enable them to go long periods without breathing.[52] Turtles share the linked circulatory and pulmonary (lung) systems of vertebrates, where the three-chambered heart pumps deoxygenated blood through the lungs and then pumps the returned oxygenated blood through the body's tissues. The cardiopulmonary system has both structural and physiological adaptations that distinguish it from other vertebrates. Turtles have a large lung volume and can move blood through non-pulmonary blood vessels, including some within the heart, to avoid the lungs while they are not breathing. They can hold their breath for much longer periods than other reptiles and they can tolerate the resulting low oxygen levels. They can moderate the increase in acidity during anaerobic (non-oxygen-based) respiration by chemical buffering and they can lie dormant for months, in aestivation or brumation.[52] The heart has two atria but only one ventricle. The ventricle is subdivided into three chambers. A muscular ridge enables a complex pattern of blood flow so that the blood can be directed either to the lungs via the pulmonary artery, or to the body via the aorta. The ability to separate the two outflows varies between species. The leatherback has a powerful muscular ridge enabling almost complete separation of the outflows, supporting its actively swimming lifestyle. The ridge is less well developed in freshwater turtles like the sliders (Trachemys).[52] Turtles are capable of enduring periods of anaerobic respiration longer than many other vertebrates. This process breaks down sugars incompletely to lactic acid, rather than all the way to carbon dioxide and water as in aerobic (oxygen-based) respiration.[52] They make use of the shell as a source of additional buffering agents for combating increased acidity, and as a sink for lactic acid.[53] Osmoregulation In sea turtles, the bladder is one unit and in most freshwater turtles, it is double-lobed.[54] Sea turtle bladders are connected to two small accessory bladders, located at the sides to the neck of the urinary bladder and above the pubis.[55] Arid-living tortoises have bladders that serve as reserves of water, storing up to 20% of their body weight in fluids. The fluids are normally low in solutes, but higher during droughts when the reptile gains potassium salts from its plant diet. The bladder stores these salts until the tortoise finds fresh drinking water.[56] To regulate the amount of salt in their bodies, sea turtles and diamondback terrapins secrete excess salt in a thick sticky substance from their tear glands. Because of this, sea turtles may appear to be "crying" when on land.[57] Thermoregulation Smaller pond turtles, like these Northern red-bellied cooters, regulate their temperature by basking in the sun. Turtles, like other reptiles, have a limited ability to regulate their body temperature. This ability varies between species, and with body size. Small pond turtles regulate their temperature by crawling out of the water and basking in the sun, while small terrestrial turtles move between sunny and shady places to adjust their temperature. Large species, both terrestrial and marine, have sufficient mass to give them substantial thermal inertia, meaning that they heat up or cool down over many hours. The Aldabra giant tortoise weighs up to some 60 kilograms (130 lb) and is able to allow its temperature to rise to some 33 °C (91 °F) on a hot day, and to fall naturally to around 29 °C (84 °F) by night. Some giant tortoises seek out shade to avoid overheating on sunny days. On Grand Terre Island, food is scarce inland, shade is scarce near the coast, and the tortoises compete for space under the few trees on hot days. Large males may push smaller females out of the shade, and some then overheat and die.[58] Adult sea turtles, too, have large enough bodies that they can to some extent control their temperature. The largest turtle, the leatherback, can swim in the waters off Nova Scotia, which may be as cold as 8 °C (46 °F), while their body temperature has been measured at up to 12 °C (54 °F) warmer than the surrounding water. To help keep their temperature up, they have a system of countercurrent heat exchange in the blood vessels between their body core and the skin of their flippers. The vessels supplying the head are insulated by fat around the neck.[58] Behavior Diet and feeding A green sea turtle grazing on seagrass Most turtle species are opportunistic omnivores; land-dwelling species are more herbivorous and aquatic ones more carnivorous.[26] Generally lacking speed and agility, most turtles feed either on plant material or on animals with limited movements like mollusks, worms, and insect larvae.[13] Some species, such as the African helmeted turtle and snapping turtles, eat fish, amphibians, reptiles (including other turtles), birds, and mammals. They may take them by ambush but also scavenge.[59] The alligator snapping turtle has a worm-like appendage on its tongue that it uses to lure fish into its mouth. Tortoises are the most herbivorous group, consuming grasses, leaves, and fruits.[60] Many turtle species, including tortoises, supplement their diet with eggshells, animal bones, hair, and droppings for extra nutrients.[61] Turtles generally eat their food in a straightforward way, though some species have special feeding techniques.[13] The yellow-spotted river turtle and the painted turtle may filter feed by skimming the water surface with their mouth and throat open to collect particles of food. When the mouth closes, the throat constricts and water is pushed out through the nostrils and the gap in between the jaws.[62] Some species employ a "gape-and-suck method" where the turtle opens its jaws and expands its throat widely, sucking the prey in.[13][63][64] The diet of an individual within a species may change with age, sex, and season, and may also differ between populations. In many species, juveniles are generally carnivorous but become more herbivorous as adults.[13][65] With Barbour's map turtle, the larger female mainly eats mollusks while the male usually eats arthropods.[13] Blanding's turtle may feed mainly on snails or crayfish depending on the population. The European pond turtle has been recorded as being mostly carnivorous much of the year but switching to water lilies during the summer.[66] Some species have developed specialized diets such as the hawksbill, which eats sponges, the leatherback, which feeds on jellyfish, and the Mekong snail-eating turtle.[26][13] Communication and intelligence The oblong turtle has a sizable vocal repertoire.[67] See also: Animal cognition While popularly thought of as mute, turtles make various sounds to communicate.[68][69] Tortoises may bellow when courting and mating.[69][30] Various species of both freshwater and sea turtles emit short, low-frequency calls from the time they are in the egg to when they are adults. These vocalizations may serve to create group cohesion when migrating.[69] The oblong turtle has a particularly large vocal range; producing sounds described as clacks, clicks, squawks, hoots, various kinds of chirps, wails, hooos, grunts, growls, blow bursts, howls, and drum rolls.[67] Play behavior has been documented in some turtle species.[70] In the laboratory, Florida red-bellied cooters can learn novel tasks and have demonstrated a long-term memory of at least 7.5 months.[71] Similarly, giant tortoises can learn and remember tasks, and master lessons much faster when trained in groups.[72] Tortoises appear to be able to retain operant conditioning nine years after their initial training.[73] Defense See also: Anti-predator adaptation Crested caracara eating a turtle When sensing danger, a turtle may flee, freeze or withdraw into its shell. Freshwater turtles flee into the water, though the Sonora mud turtle may take refuge on land as the shallow temporary ponds they inhabit make them vulnerable.[74] When startled, a softshell turtle may dive underwater and bury itself under the sea floor.[75] If a predator persists, the turtle may bite or discharge from its cloaca. Several species produce foul-smelling chemicals from musk glands. Other tactics include threat displays and Bell's hinge-back tortoise can play dead. When attacked, big-headed turtle hatchlings squeal, possibly startling the predator.[76] Migration Further information: Sea turtle migration Turtles are the only reptiles that migrate long distances, more specifically the marine species that can travel up to thousands of kilometers. Some non-marine turtles, such as the species of Geochelone (terrestrial), Chelydra (freshwater), and Malaclemys (estuarine), migrate seasonally over much shorter distances, up to around 27 km (17 mi), to lay eggs. Such short migrations are comparable to those of some lizards, snakes, and crocodilians.[77] Sea turtles nest in a specific area, such as a beach, leaving the eggs to hatch unattended. The young turtles leave that area, migrating long distances in the years or decades in which they grow to maturity, and then return seemingly to the same area every few years to mate and lay eggs, though the precision varies between species and populations. This "natal homing" has appeared remarkable to biologists, though there is now plentiful evidence for it, including from genetics.[78] How sea turtles navigate to their breeding beaches remains unknown. One possibility is imprinting as in salmon, where the young learn the chemical signature, effectively the scent, of their home waters before leaving, and remember that when the time comes for them to return as adults. Another possible cue is the orientation of the earth's magnetic field at the natal beach. There is experimental evidence that turtles have an effective magnetic sense, and that they use this in navigation. Proof that homing occurs is derived from genetic analysis of populations of loggerheads, hawksbills, leatherbacks, and olive ridleys by nesting place. For each of these species, the populations in different places have their own mitochondrial DNA genetic signatures that persist over the years. This shows that the populations are distinct and that homing must be occurring reliably.[78] Reproduction and lifecycle Two frames from a film showing desert tortoises fighting. One tortoise bites the other Desert tortoises fighting Turtles have a wide variety of mating behaviors but do not form pair-bonds or social groups.[79] In green sea turtles, females generally outnumber males.[80] In terrestrial species, males are often larger than females and fighting between males establishes a dominance hierarchy for access to mates. For most semi-aquatic and bottom-walking aquatic species, combat occurs less often. Males of these species instead may use their size advantage to mate forcibly. In fully aquatic species, males are often smaller than females and rely on courtship displays to gain mating access to females.[81] Courtship and mounting Courtship varies between species, and with habitat. It is often complex in aquatic species, both marine and freshwater, but simpler in the semi-aquatic mud turtles and snapping turtles. A male tortoise bobs his head, then subdues the female by biting and butting her before mounting.[13] The male scorpion mud turtle approaches the female from the rear, and often resorts to aggressive methods such as biting the female's tail or hind limbs, followed by a mounting.[82] Female choice is important in some species, and female green sea turtles are not always receptive. As such, they have evolved behaviors to avoid the male's attempts at copulation, such as swimming away, confronting the male followed by biting or taking up a refusal position with her body vertical, her limbs widely outspread, and her plastron facing the male. If the water is too shallow for the refusal position, the females resort to beaching themselves, as the males do not follow them ashore.[80] Photograph of a male turtle mounting a female Mounting behavior in the three-toed box turtle All turtles fertilize internally; mounting and copulation can be difficult. In many species, males have a concave plastron that interlocks with the female's carapace. In species like the Russian tortoise, the male has a lighter shell and longer legs. The high, rounded shape of box turtles are particular obstacles for mounting. The male eastern box turtle leans backward and hooks onto the back of the female's plastron.[83] Aquatic turtles mount in water,[84][85] and female sea turtles support the mounting male while swimming and diving.[86] During copulation, the male turtle aligns his tail with the female's so he can insert his penis into her cloaca.[87] Some female turtles can store sperm from multiple males and their egg clutches can have multiple sires.[88][79] Eggs and hatchlings land turtle laying an egg in a hole A female common snapping turtle depositing her eggs in a hole she dug Turtles, including sea turtles, lay their eggs on land, although some lay eggs close near water that rises and falls in level, submerging the eggs. While most species build nests and lay eggs where they forage, some travel miles. The common snapping turtle walks 5 km (3 mi) on land, while sea turtles travel even further; the leatherback swims some 12,000 km (7,500 mi) to its nesting beaches.[13][85] Most turtles create a nest for their eggs. Females usually dig a flask-like chamber in the substrate. Other species lay their eggs in vegetation or crevices.[89] Females choose nesting locations based on environmental factors such as temperature and humidity, which are important for developing embryos.[85] Depending on the species, the number of eggs laid varies from one to over 100. Larger females can lay eggs that are greater in number or bigger in size. Compared to freshwater turtles, tortoises deposit fewer but larger eggs. Females can lay multiple clutches throughout a season, particularly in species that experience unpredictable monsoons.[90] Tortoise hatching from egg Marginated tortoise emerges from its egg Most mother turtles do no more in the way of parental care than covering their eggs and immediately leaving, though some species guard their nests for days or weeks.[91] Eggs vary between rounded, oval, elongated, and between hard- and soft-shelled.[92] Most species have their sex determined by temperature. In some species, higher temperatures produce females and lower ones produce males, while in others, milder temperatures produce males and both hot and cold extremes produce females.[13] There is experimental evidence that the embryos of Mauremys reevesii can move around inside their eggs to select the best temperature for development, thus influencing their sexual destiny.[93] In other species, sex is determined genetically. The length of incubation for turtle eggs varies from two to three months for temperate species, and four months to over a year for tropical species.[13] Species that live in warm temperate climates can delay their development.[94] Hatching young turtles break out of the shell using an egg tooth, a sharp projection that exists temporarily on their upper beak.[13][95] Hatchlings dig themselves out of the nest and find safety in vegetation or water. Some species stay in the nest for longer, be it for overwintering or to wait for the rain to loosen the soil for them to dig out.[13] Young turtles are highly vulnerable to predators, both in the egg and as hatchlings. Mortality is high during this period but significantly decreases when they reach adulthood. Most species grow quickly during their early years and slow down when they are mature.[96] Lifespan Turtles can live long lives. The oldest living turtle and land animal is said to be a Seychelles giant tortoise named Jonathan, who turned 187 in 2019.[97] A Galápagos tortoise named Harriet was collected by Charles Darwin in 1835; it died in 2006, having lived for at least 176 years. Most wild turtles do not reach that age. Turtles keep growing new scutes under the previous scutes every year, allowing researchers to estimate how long they have lived.[98] They also age slowly.[99] The survival rate for adult turtles can reach 99% per year.[13] Systematics and evolution Further information: Turtle classification and List of Testudines families Fossil history Diagram of evolution of turtle shells showing four fossil species Diagram of the origins of the turtle body plan through the Triassic: isolated bony plates evolved to form a complete shell, in a sequence involving Pappochelys, Eorhynchochelys, Odontochelys, and Proganochelys.[19] Zoologists have sought to explain the evolutionary origin of the turtles, and in particular of their unique shells. In 1914, Jan Versluys proposed that bony plates in the dermis, called osteoderms, fused to the ribs beneath them, later called the "Polka Dot Ancestor" by Olivier Rieppel.[19][100] The theory accounted for the evolution of fossil pareiasaurs from Bradysaurus to Anthodon, but not for how the ribs could have become attached to the bony dermal plates.[19] More recent discoveries have painted a different scenario for the evolution of the turtle's shell. The stem-turtles Eunotosaurus of the Middle Permian, Pappochelys of the Middle Triassic, and Eorhynchochelys of the Late Triassic lacked carapaces and plastrons but had shortened torsos, expanded ribs, and lengthened dorsal vertebrae. Also in the Late Triassic, Odontochelys had a partial shell consisting of a complete bony plastron and an incomplete carapace. The development of a shell reached completion with the Late Triassic Proganochelys, with its fully developed carapace and plastron.[19][101] Adaptations that lead to the evolution of the shell may have originally been for digging and a fossorial lifestyle.[101] The oldest known members of the Pleurodira lineage are the Platychelyidae, from the Late Jurassic.[102] The oldest known unambiguous cryptodire is Sinaspideretes, a close relative of softshell turtles, from the Late Jurassic of China.[103] During the Late Cretaceous and Cenozoic, members of the pleurodire families Bothremydidae and Podocnemididae became widely distributed in the Northern Hemisphere due to their coastal habits.[104][105] The oldest known soft-shelled turtles and sea turtles appeared during the Early Cretaceous.[106][107] Tortoises originated in Asia during the Eocene.[108] A late surviving group of stem-turtles, the Meiolaniidae, survived in Australasia into the Pleistocene and Holocene.[109] External relationships The turtles' exact ancestry has been disputed. It was believed they were the only surviving branch of the ancient evolutionary grade Anapsida, which includes groups such as procolophonids and pareiasaurs. All anapsid skulls lack a temporal opening while all other living amniotes have temporal openings.[110] It was later suggested that the anapsid-like turtle skulls may be due to backward evolution rather than to anapsid descent.[111] Fossil evidence has shown that early stem-turtles possessed small temporal openings.[101] Some early morphological phylogenetic studies have placed turtles closer to Lepidosauria (tuataras, lizards, and snakes) than to Archosauria (crocodilians and birds).[110] By contrast, several molecular studies place turtles either within Archosauria,[112] or, more commonly, as a sister group to extant archosaurs,[111][113][114][115] though an analysis conducted by Tyler Lyson and colleagues (2012) recovered turtles as the sister group of lepidosaurs instead.[116] Ylenia Chiari and colleagues (2012) analyzed 248 nuclear genes from 16 vertebrates and suggested that turtles share a more recent common ancestor with birds and crocodilians. The date of separation of turtles and birds and crocodilians was estimated to be 255 million years ago during the Permian.[117] Through genomic-scale phylogenetic study of ultra-conserved elements (UCEs) to clarify the placement of turtles within reptiles, Nicholas Crawford and colleagues (2012) similarly found that turtles are closer to birds and crocodilians.[118] Using the draft (unfinished) genome sequences of the green sea turtle and the Chinese softshell turtle, Zhuo Wang and colleagues (2013) concluded that turtles are likely a sister group of crocodilians and birds.[119] The external phylogeny of the turtles is shown in the cladogram below.[118] Diapsida Archosauromorpha     Crocodilia (crocodiles, alligators) Deinosuchus riograndensis.png     Aves (birds) Spot-billed pelican takeoff white background.jpg       Testudines Psammobates geometricus 1872 white background.jpg     Lepidosauromorpha Squamata (lizards, snakes) Zoology of Egypt (1898) (Varanus exanthematicus).png     Internal relationships Modern turtles and their extinct relatives with a complete shell are classified within the clade Testudinata.[120] The most recent common ancestor of living turtles, corresponding to the split between Pleurodira (side-necked species) and Cryptodira (hidden necked species), is estimated to have occurred around 210 million years ago during the Late Triassic.[121] Robert Thompson and colleagues (2021) comment that living turtles have low diversity, relative to how long they existed. Diversity has been stable, according to their analysis, except for a single rapid increase around the Eocene-Oligocene boundary some 30 million years ago, and a large regional extinction at roughly the same time. They suggest that global climate change caused both events, as the cooling and drying caused the land to become arid and turtles to become extinct there, while new continental margins opened up by the climate change provided habitats for other species to evolve.[122] The cladogram, from Nicholas Crawford and colleagues 2015, shows the internal phylogeny of the Testudines down to the level of families.[123][124] The analysis by Thompson and colleagues in 2021 supports the same structure down to the family level.[122] Testudines Pleurodira     Pelomedusidae Erpétologie générale, ou, Histoire naturelle complète des reptiles (Pelomedusa subrufa).jpg     Podocnemididae Erpétologie générale, ou, Histoire naturelle complète des reptiles (Podocnemis expansa).jpg       Chelidae Erpétologie générale, ou, Histoire naturelle complète des reptiles (Chelus fimbriata).jpg   (Side‑necked turtles) Cryptodira       Testudinoidea   Testudinidae Erpétologie générale, ou, Histoire naturelle complète des reptiles (Centrochelys sulcata).jpg (Tortoises) Geoemydidae Erpétologie générale, ou, Histoire naturelle complète des reptiles (Morenia ocellata).jpg       Platysternidae Erpétologie générale, ou, Histoire naturelle complète des reptiles (Platysternon megacephalum).jpg   Emydidae Emydoidea blandingiiHolbrookV1P03A flipped.jpg (Terrapins)         Chelydroidea   Chelydridae Erpétologie générale, ou, Histoire naturelle complète des reptiles (Chelydra serpentina).jpg (Snapping turtles)     Dermatemydidae ChloremysAbnormisFord white background.jpg     Kinosternidae Erpétologie générale, ou, Histoire naturelle complète des reptiles (Sternotherus odoratus).jpg       Chelonioidea Dermochelyidae Erpétologie générale, ou, Histoire naturelle complète des reptiles (Dermochelys coriacea).jpg (Leatherback) Cheloniidae Erpétologie générale, ou, Histoire naturelle complète des reptiles (Chelonia mydas).jpg   (Sea turtles)   (Hardshell turtles) Trionychia Carettochelyidae Pig-nosed turtle (Carettochelys insculpta) (cropped).jpg (Pig‑nosed turtle) Trionychidae Erpétologie générale, ou, Histoire naturelle complète des reptiles (Lissemys punctata).jpg   (Softshell turtles)   (Hidden‑necked turtles)   Differences between the two suborders Neck retraction Photograph of a cryptodiran with its head pulled back straight into its shell Cryptodira retract their necks backward. Photograph of a pleurodiran with its head and neck folded toward the side Pleurodira retract their necks sideways. Diagrams of the top-down bending of the neck of cryptodirans, and the left-right bending of the neck in pleurodirans The different mechanisms of neck retraction in the two suborders of turtles Turtles are divided into two living suborders: Cryptodira and Pleurodira.[125] The two groups differ in the way the neck is retracted for protection. Pleurodirans retract their neck to the side and in front of the shoulder girdles, whereas cryptodirans retract their neck backward into their shell. These motions are enabled by the morphology and arrangement of neck vertebrae.[126][127] Sea turtles (which belong to Cryptodira) have mostly lost the ability to retract their heads.[128] The adductor muscles in the lower jaw create a pulley-like system in both subgroups. However, the bones that the muscles articulate with differ. In Pleurodira, the pulley is formed with the pterygoid bones of the palate, but in Cryptodira the pulley is formed with the otic capsule. Both systems help to vertically redirect the adductor muscles and maintain a powerful bite.[129] A further difference between the suborders is the attachment of the pelvis. In Cryptodira, the pelvis is free, linked to the shell only by ligaments. In Pleurodira, the pelvis is sutured, joined with bony connections, to the carapace and to the plastron, creating a pair of large columns of bone at the back end of the turtle, linking the two parts of the shell.[130] Distribution and habitat Turtles are widely distributed across the world's continents, oceans, and islands with terrestrial, fully aquatic, and semi-aquatic species. Sea turtles are mainly tropical and subtropical, but leatherbacks can be found in colder areas of the Atlantic and Pacific.[131] Living Pleurodira all live in freshwater and are found only in the Southern Hemisphere.[132] The Cryptodira include terrestrial, freshwater, and marine species, and these range more widely.[131] The world regions richest in non-marine turtle species are the Amazon basin, the Gulf of Mexico drainages of the United States, and parts of South and Southeast Asia.[133] For turtles in colder climates, their distribution is limited by constraints on reproduction, which is reduced by long hibernations. North American species barely range above the southern Canadian border.[134] Some turtles are found at high altitudes, for example, the species Terrapene ornata occurs up to 2,000 m (6,600 ft) in New Mexico.[135] Conversely, the leatherback sea turtle can dive over 1,200 m (3,900 ft).[136] Species of the genus Gopherus can tolerate both below freezing and over 40 °C (104 °F) in body temperature, though they are most active at 26–34 °C (79–93 °F).[137] Conservation Photograph of a marine turtle escaping from a specially-designed fishing net Many turtles have been killed accidentally in fishing nets.[138] Some trawlers now use nets fitted with turtle excluders.[139] Seen here, a loggerhead escapes a net so fitted. Among vertebrate orders, turtles are second only to primates in the percentage of threatened species. 360 modern species have existed since 1500 AD. Of these, 51–56% are considered threatened and 60% considered threatened or extinct.[140] Turtles face many threats, including habitat destruction, harvesting for consumption, the pet trade,[141][142] light pollution,[143] and climate change.[144] Asian species have a particularly high extinction risk, primarily due to their long-term unsustainable exploitation for food and medicine,[145] and about 83% of Asia's non-marine turtle species are considered threatened.[140] As of 2021, turtle extinction is progressing much faster than during the Cretaceous-Tertiary extinction. At this rate, all turtles could be extinct in a few centuries.[146] Turtle hatcheries can be set up when protection against flooding, erosion, predation, or heavy poaching is required.[147][148][149] Chinese markets have sought to satisfy an increasing demand for turtle meat with farmed turtles. In 2007 it was estimated that over a thousand turtle farms operated in China.[150] All the same, wild turtles continue to be caught and sent to market in large numbers, resulting in what conservationists have called "the Asian turtle crisis".[151][145] In the words of the biologist George Amato, the hunting of turtles "vacuumed up entire species from areas in Southeast Asia", even as biologists still did not know how many species lived in the region.[152] In 2000, all the Asian box turtles were placed on the CITES list of endangered species.[145] Harvesting wild turtles is legal in some American states,[153] and there has been a growing demand for American turtles in China.[154][155] The Florida Fish and Wildlife Conservation Commission estimated in 2008 that around 3,000 pounds of softshell turtles were exported weekly via Tampa International Airport.[155] However, the great majority of turtles exported from the US between 2002 and 2005 were farmed.[154] Large numbers of sea turtles are accidentally killed in longlines, gillnets, and trawling nets as bycatch. A 2010 study suggested that over 8 million had been killed between 1990 and 2008; the Eastern Pacific and the Mediterranean were identified as among the areas worst affected.[138] Since the 1980s, the United States has required all shrimp trawlers to fit their nets with turtle excluder devices that prevent turtles from being entangled in the net and drowning.[139] More locally, other human activities are affecting marine turtles. In Australia, Queensland's shark culling program, which uses shark nets and drum lines, has killed over 5,000 turtles as bycatch between 1962 and 2015; including 719 loggerhead turtles and 33 hawksbill sea turtles, which are listed as critically endangered.[156] Native turtle populations can also be threatened by invasive ones. The central North American red-eared slider turtle has been listed among the "world's worst invasive species", pet turtle having been released globally. They appear to compete with native turtle species in eastern and western North America, Europe, and Japan.[157][158] Human uses In culture Main article: Cultural depictions of turtles Further information: World Turtle Photograph of temple sculpture in India 4th-century sculpture of turtle avatar of Vishnu. Garhwa, India Lithograph drawing of world resting on 4 elephants standing on a giant turtle World resting on four elephants on the back of the World Turtle. Western depiction of "The Hindu Earth", 1877 Chinese funeral stone held up by a stone tortoise Bixi supporting Kangxi Emperor's stele, Beijing, 1698 Children's book illustration with turtle figure standing on hind legs The Mock Turtle in Lewis Carroll's 1865 Alice's Adventures in Wonderland Painting of a turtle standing on hind legs, with top hat and cane, on theatre poster Poster for 1898 production of The Turtle at the Manhattan Theatre, Broadway Photograph of cloth with four terrapin shell rattles to be tied around a dancer's leg Terrapin shell leg rattles worn by lead Cherokee woman dancer, 20th century Turtles have featured in human cultures across the world since ancient times. They are generally viewed positively despite not being "cuddly" or flashy; their association with the ancient times and old age have contributed to their endearing image.[159] In Hindu mythology, the World Turtle, named Kurma or Kacchapa, supports four elephants on his back; they, in turn, carry the weight of the whole world on their backs.[160][161] The turtle is one of the ten avatars or incarnations of the god Vishnu.[160] The yoga pose Kurmasana is named for the avatar.[162][163] World Turtles are found in Native American cultures including the Algonquian, Iroquois, and Lenape. They tell many versions of the creation story of Turtle Island. One version has Muskrat pile up earth on Turtle's back, creating the continent of North America. An Iroquois version has the pregnant Sky Woman fall through a hole in the sky between a tree's roots, where she is caught by birds who land her safely on Turtle's back; the Earth grows around her. The turtle here is altruistic, but the world is a heavy burden, and the turtle sometimes shakes itself to relieve the load, causing earthquakes.[160][164][165] A turtle was the symbol of the Ancient Mesopotamian god Enki from the 3rd millennium BCE onward.[166] An ancient Greek origin myth told that only the tortoise refused the invitation of the gods Zeus and Hera to their wedding, as it preferred to stay at home. Zeus then ordered it to carry its house with it, ever after.[167] Another of their gods, Hermes, invented a seven-stringed lyre made with the shell of a tortoise.[168] In the Shang dynasty Chinese practice of plastromancy, dating back to 1200 BCE, oracles were obtained by inscribing questions on turtle plastrons using the oldest known form of Chinese characters, burning the plastron, and interpreting the resulting cracks. Later, the turtle was one of the four sacred animals in Confucianism, while in the Han period, steles were mounted on top of stone turtles, later linked with Bixi, the turtle-shelled son of the Dragon King.[169] Marine turtles feature significantly in Australian Aboriginal art.[161] The army of Ancient Rome used the testudo ("tortoise") formation where soldiers would form a shield wall for protection.[158] In Aesop's Fables, "The Tortoise and the Hare" tells how an unequal race may be won by the slower partner.[170][171] Lewis Carroll's 1865 Alice's Adventures in Wonderland features a Mock Turtle, named for a soup meant to imitate the expensive soup made from real turtle meat.[172][173][174] In 1896, the French playwright Léon Gandillot wrote a comedy in three acts named La Tortue that was "a Parisian sensation"[175] in its run in France, and came to the Manhattan Theatre, Broadway, New York, in 1898 as The Turtle.[176] A "cosmic turtle" and the island motif reappear in Gary Snyder's 1974 novel Turtle Island, and again in Terry Pratchett's Discworld series as Great A'Tuin, starting with the 1983 novel The Colour of Magic. It is supposedly of the species Chelys galactica, the galactic turtle, complete with four elephants on its back to support Discworld.[177] Turtles have been featured in comic books and animations such as the 1984 Teenage Mutant Ninja Turtles.[178][179] As pets Some turtles, particularly small terrestrial and freshwater species, are kept as pets.[180][181] The demand for pet turtles increased in the 1950s, with the US being the main supplier, particularly of farm-bred red-eared sliders. The popularity for exotic pets has led to an increase in illegal wildlife trafficking. Around 21% of the value of live animal trade is in reptiles, and turtles are among the more popularly traded species.[182] Poor husbandry of tortoises can cause chronic rhinitis (nasal swelling), overgrown beaks, hyperparathyroidism (which softens their skeleton), constipation, various reproductive problems, and injuries from dogs.[180] In the early 20th century, people in the United States have organized and gambled on turtle races.[183] As food and other uses The flesh of captured wild turtles continues to be eaten in Asian cultures,[184] while turtle soup was once a popular dish in English cuisine.[185] Gopher tortoise stew has been popular with some groups in Florida.[186] The supposed aphrodisiac or medicinal properties of turtle eggs created a large trade for them in Southeast Asia.[161] Hard-shell turtle plastrons and soft-shell carapaces are widely used in traditional Chinese medicine; Taiwan imported nearly 200 metric tons of hard-shells from its neighbors yearly from 1999 to 2008.[187] A popular medicinal preparation based on herbs and turtle shells is guilinggao jelly.[188] The substance tortoiseshell, usually from the hawksbill turtle, has been used for centuries to make jewelry, tools, and ornaments around the Western Pacific.[161] Hawksbills have accordingly been hunted for their shells.[189] The trading of tortoiseshell was internationally banned in 1977 by CITES.[190] Some cultures have used turtle shells to make music: Native American shamans made them into ceremonial rattles, while Aztecs, Mayas, and Mixtecs made ayotl drums.[191]

Fishareaquatic,craniate,gill-bearing animals that lacklimbswithdigits. Included in this definition are the livinghagfish,lampreys, andcartilaginousandbony fishas well as various extinct related groups. Approximately 95% of living fish species are ray-finned fish, belonging to the classActinopterygii, with around 99% of those beingteleosts. Fish Temporal range:535–0Ma PreꞒ Ꞓ O S D C P T J K Pg N Middle Cambrian-Recent Giant grouperswimming amongschoolsof other fishHead-on view of ared lionfishScientific classificationKingdom:AnimaliaPhylum:ChordataClade:OlfactoresSubphylum:VertebrataGroups includedJawless fish†Armoured fish†Spiny sharksCartilaginous fishBony fishRay-finned fishLobe-finned fishCladisticallyincluded but traditionally excluded taxaTetrapods†Conodonts The earliest organisms that can be classified as fish were soft-bodiedchordatesthat first appeared during theCambrianperiod. Although they lacked atrue spine, they possessednotochordswhich allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through thePaleozoicera, diversifying into a wide variety of forms. Many fish of the Paleozoic developedexternal armorthat protected them from predators. The first fish withjawsappeared in theSilurianperiod, after which many (such assharks) became formidable marine predators rather than just the prey ofarthropods. Most fish areectothermic("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers likewhite sharkandtunacan hold a highercore temperature.[1][2]Fish can acoustically communicate with each other, most often in the context of feeding, aggression or courtship.[3] Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g.,charandgudgeon) to theabyssaland evenhadaldepths of the deepest oceans (e.g.,cusk-eelsandsnailfish), although no species has yet been documented in the deepest 25% of the ocean.[4]With 34,300 described species, fish exhibit greater species diversity than any other group of vertebrates.[5] Fish are an important resource for humans worldwide, especiallyas food. Commercial and subsistence fishers hunt fish inwild fisheriesorfarmthem in ponds or in cages in the ocean (inaquaculture). They are also caught byrecreational fishers, kept as pets, raised byfishkeepers, and exhibited in publicaquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies. Tetrapods(amphibians,reptiles,birdsandmammals) emerged withinlobe-finned fishes, socladisticallythey are fish as well. However, traditionally fish (piscesorichthyes) are renderedparaphyleticby excluding the tetrapods, and are therefore not considered a formal taxonomic grouping insystematic biology, unless it is used in thecladisticsense, including tetrapods,[6][7]although usually "vertebrate" is preferred and used for this purpose (fish plus tetrapods) instead. Furthermore,cetaceans, although mammals, have often been considered fish by various cultures and timeperiods. Contents Etymology The word forfishin English and the otherGermanic languages(GermanFisch;Gothicfisks) is inherited fromProto-Germanic, and is related to theLatinpiscisandOld Irishīasc, though the exact root is unknown; some authorities reconstruct anProto-Indo-Europeanroot*peysk-, attested only inItalic,Celtic, andGermanic.[8][9][10][11] The English word once had a much broader usage than its current biological meaning. Names such asstarfish,jellyfish,shellfishandcuttlefishattest to almost any fully aquatic animal (including whales) once beingfish. "Correcting" such names (e.g. tosea star) is an attempt to retroactively apply the current meaning offishto words that were coined when it had a different meaning. Evolution Main article:Evolution of fish Fish, as vertebrata, developed as sister of the tunicata. As the tetrapods emerged deep within the fishes group, as sister of the lungfish, characteristics of fish are typically shared by tetrapods, including having vertebrae and a cranium.  Dunkleosteuswas a gigantic, 10-metre (33ft) longprehistoric fishof class Placodermi.  Lower jaw of the placodermEastmanosteuspustulosus, showing the shearing structures ("teeth") on its oral surface; from theDevonianofWisconsin Early fish from the fossil record are represented by a group of small, jawless, armored fish known asostracoderms. Jawless fish lineages are mostly extinct. An extant clade, thelampreysmay approximate ancient pre-jawed fish. The first jaws are found inPlacodermifossils. They lacked distinct teeth, having instead the oral surfaces of their jaw plates modified to serve the various purposes of teeth. The diversity of jawed vertebrates may indicate the evolutionary advantage of ajawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors. Fish may have evolved from a creature similar to a coral-likesea squirt, whose larvae resemble primitive fish in important ways. The first ancestors of fish may havekept the larval form into adulthood(as some sea squirts do today). Phylogeny Fishes are aparaphyleticgroup: that is, anycladecontaining all fish also contains thetetrapods, which are not fish (though they include fish-shaped forms, such asWhales and Dolphinsor theextinctichthyosaurs, which acquired a fish-like body shape due tosecondary aquatic adaptation, seeevolution of cetaceans). The followingcladogramshowsclades- some with, some withoutextantrelatives - that are traditionally considered as "fishes" (cyanline) and the tetrapods (four-limbed vertebrates), which are mostly terrestrial.Extinctgroups are marked with adagger(†). Vertebrata/ Agnatha/  Hyperoartia(lampreys)    Myxini(hagfish)  Cyclostomes   †Euconodonta     †Pteraspidomorphi    †Thelodonti     †Anaspida     †Galeaspida     †Pituriaspida    †Osteostraci  Gnathostomata  "†Placodermi" (armoured fishes,paraphyletic)[13]     "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)[14]   Chondrichthyes  "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)     Holocephali(ratfish)    Euselachii(sharks,rays)   (cartilaginousfishes)Euteleostomi/  "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)    Actinopterygii  Cladistia(bichirs,reedfish)     Chondrostei(sturgeons,paddlefish)    Neopterygii(includesTeleostei, 96% of living fishspecies)   (ray‑finnedfishes)Sarcopterygii  †Onychodontiformes    Actinistia(coelacanths)  Rhipidistia   †Porolepiformes    Dipnoi(lungfishes)   Tetrapodomorpha/   †Rhizodontimorpha     †Tristichopteridae     †Tiktaalik  Tetrapoda  †Ichthyostega    crown-grouptetrapods  four‑limbedvertebrates   (Choanata) (lobe‑finnedfish)  Osteichthyes  (jawedvertebrates)     "Fishes" Craniata Taxonomy  Leedsichthys,of the subclass Actinopterygii, is the largest known fish, with estimates in 2005 putting its maximum size at 16 metres (52ft). Fishes are aparaphyleticgroup and for this reason, groups such as the classPiscesseen in older reference works are no longer used in formal classifications. Traditional classification divides fish into threeextantclasses, and with extinct forms sometimes classified within the tree, sometimes as their own classes:[15][16] ClassAgnatha(jawless fish) SubclassCyclostomata(hagfishandlampreys) SubclassOstracodermi(armoured jawless fish) † ClassChondrichthyes(cartilaginous fish) SubclassElasmobranchii(sharksandrays) SubclassHolocephali(chimaerasand extinct relatives) ClassPlacodermi(armoured fish) † ClassAcanthodii("spiny sharks", sometimes classified under bony fishes)† ClassOsteichthyes(bony fish) SubclassActinopterygii(ray finned fishes) SubclassSarcopterygii(fleshy finned fishes, ancestors of tetrapods) The above scheme is the one most commonly encountered in non-specialist and general works. Many of the above groups are paraphyletic, in that they have given rise to successive groups: Agnathans are ancestral to Chondrichthyes, who again have given rise to Acanthodiians, the ancestors of Osteichthyes. With the arrival ofphylogenetic nomenclature, the fishes has been split up into a more detailed scheme, with the following major groups: Class Myxini (hagfish) ClassPteraspidomorphi† (early jawless fish) ClassThelodonti† ClassAnaspida† ClassPetromyzontida or Hyperoartia Petromyzontidae (lampreys) ClassConodonta(conodonts) † ClassCephalaspidomorphi† (early jawless fish) (unranked)Galeaspida† (unranked)Pituriaspida† (unranked)Osteostraci† InfraphylumGnathostomata(jawed vertebrates) ClassPlacodermi† (armoured fish) ClassChondrichthyes(cartilaginous fish) ClassAcanthodii† (spiny sharks) SuperclassOsteichthyes(bony fish) ClassActinopterygii(ray-finned fish) SubclassChondrostei OrderAcipenseriformes(sturgeonsandpaddlefishes) OrderPolypteriformes(reedfishesandbichirs). SubclassNeopterygii InfraclassHolostei(garsandbowfins) InfraclassTeleostei(many orders of common fish) ClassSarcopterygii(lobe-finned fish) SubclassActinistia(coelacanths) Subclass Dipnoi (lungfish, sister group to thetetrapods) † – indicates extinct taxon Some palaeontologists contend that becauseConodontaarechordates, they are primitive fish. For a fuller treatment of this taxonomy, see thevertebratearticle. The position ofhagfishin the phylum Chordata is not settled. Phylogenetic research in 1998 and 1999 supported the idea that the hagfish and the lampreys form a natural group, theCyclostomata, that is a sister group of the Gnathostomata.[17][18] The various fish groups account for more than half of vertebrate species. As of 2006,[19]there are almost 28,000 knownextantspecies, of which almost 27,000 are bony fish, with 970sharks, rays, and chimerasand about 108 hagfish and lampreys. A third of these species fall within the nine largest families; from largest to smallest, these families areCyprinidae,Gobiidae,Cichlidae,Characidae,Loricariidae,Balitoridae,Serranidae,Labridae, andScorpaenidae. About 64 families aremonotypic, containing only one species. The final total of extant species may grow to exceed 32,500.[20]Each year, newspeciesare discovered andscientifically described. As of 2016,[21]there are over 32,000 documented species of bony fish and over 1,100 species of cartilaginous fish. Species are lost throughextinction(seebiodiversity crisis). Recent examples are theChinese paddlefishor thesmooth handfish. Diversity Main article:Diversity of fish  Agnatha (Pacific hagfish)  Chondrichthyes (Horn shark)  Actinopterygii (Brown trout)  Sarcopterygii (Coelacanth)  A relative of the seahorses, theleafy seadragon's appendages allow it to camouflage (in the form ofcrypsis) with the surroundingseaweed.  The psychedelicmandarin dragonetis one of only two animal species known to have blue colouring because of cellular pigment.[22] The term "fish" most precisely describes any non-tetrapodcraniate(i.e. an animal with a skull and in most cases a backbone) that hasgillsthroughout life and whose limbs, if any, are in the shape of fins.[23]Unlike groupings such as birds ormammals, fish are not a singlecladebut aparaphyleticcollection oftaxa, includinghagfishes,lampreys,sharks and rays,ray-finned fish,coelacanths, andlungfish.[24][25]Indeed, lungfish and coelacanths are closer relatives oftetrapods(such as mammals, birds,amphibians, etc.) than of other fish such as ray-finned fish or sharks, so thelast common ancestorof all fish is also an ancestor to tetrapods. As paraphyletic groups are no longer recognised in modernsystematic biology, the use of the term "fish" as a biological group must be avoided. Many types ofaquatic animalscommonly referred to as "fish" are not fish in the sense given above; examples includeshellfish,cuttlefish,starfish,crayfishandjellyfish. In earlier times, even biologists did not make a distinction– sixteenth century natural historians classified alsoseals, whales,amphibians,crocodiles, evenhippopotamuses, as well as a host of aquatic invertebrates, as fish.[26]However, according to the definition above, all mammals, includingcetaceanslike whales and dolphins, are not fish. In some contexts, especially inaquaculture, the true fish are referred to asfinfish(orfin fish) to distinguish them from these other animals. A typical fish isectothermic, has astreamlinedbody for rapid swimming, extracts oxygen from water using gills or uses an accessory breathing organ to breathe atmospheric oxygen, has two sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin, and a tail fin, has jaws, has skin that is usually covered withscales, and lays eggs. Each criterion has exceptions.Tuna,swordfish, and some species ofsharksshowsome warm-blooded adaptations– they can heat their bodies significantly above ambient water temperature.[24]Streamlining and swimming performance varies from fish such as tuna,salmon, andjacksthat can cover 10–20 body-lengths per second to species such aseelsandraysthat swim no more than 0.5 body-lengths per second.[27]Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures.Lungfishhave paired lungs similar to those of tetrapods,gouramishave a structure called thelabyrinth organthat performs a similar function, while many catfish, such asCorydorasextract oxygen via the intestine or stomach.[28]Body shape and the arrangement of the fins is highly variable, covering such seemingly un-fishlike forms asseahorses,pufferfish,anglerfish, andgulpers. Similarly, the surface of the skin may be naked (as inmoray eels), or covered with scales of a variety of different types usually defined asplacoid(typical of sharks and rays),cosmoid(fossil lungfish and coelacanths),ganoid(various fossil fish but also livinggarsandbichirs),cycloid, andctenoid(these last two are found on mostbony fish).[29]There are even fish that live mostly on land or lay their eggs on land near water.[30]Mudskippersfeed and interact with one another on mudflats and go underwater to hide in their burrows.[31]A singleundescribed speciesofPhreatobiushas been called a true "land fish" as this worm-like catfish strictly lives among waterloggedleaf litter.[32][33]Many species live inunderground lakes,underground riversoraquifersand are popularly known ascavefish.[34] Fish range in size from the huge 16-metre (52ft)whale sharkto the tiny 8-millimetre (0.3in)stout infantfish. Fishspeciesdiversity is roughly divided equally between marine (oceanic) andfreshwaterecosystems.Coral reefsin theIndo-Pacificconstitute the center of diversity for marine fishes, whereas continental freshwater fishes are most diverse in largeriver basinsoftropical rainforests, especially theAmazon,Congo, andMekongbasins. More than 5,600 fish species inhabitNeotropicalfreshwaters alone, such thatNeotropical fishesrepresent about 10% of allvertebratespecies on the Earth. Exceptionally rich sites in the Amazon basin, such asCantão State Park, can contain more freshwater fish species than occur in all of Europe.[35] The deepest living fish in the ocean so far found is the Mariana snailfish (Pseudoliparis swirei) which lives at deeps of 8,000 meters (26,200 feet) along the Mariana Trench near Guam.[36] Thediversityof living fish (finfish) is unevenly distributed among the various groups, withteleostsmaking up the bulk of living fishes (96%), and over 50% of allvertebratespecies.[21]The followingcladogram[37]shows theevolutionary relationshipsof all groups of living fishes (with their respective diversity[21]) and the four-limbed vertebrates (tetrapods).  Diversityof various groups of fish (and othervertebrates) through time  Lungfishare the closest living relatives oftetrapods(four-limbed vertebrates).  ThebowfinAmia calvais the sole survivor of thehalecomorphclade. Vertebrates  Jawless fish(118 living species:hagfish,lampreys)  Jawedvertebrates  Cartilaginous fishes(>1,100 living species:sharks,rays,chimaeras)  Bonyfishes Lobe-finfishRhipidistia  Tetrapoda(>30,000 living species:amphibians,mammals,reptiles,birds)    Dipnoi(6 living species:lungfish)     Actinistia(2 living species:coelacanths)   Ray-finfish  Cladistia(14 living species:bichirs,reedfish)  Actinopteri  Chondrostei(27 living species:sturgeons,paddlefish)  Neopterygii Holostei  Ginglymodi(7 living species:gars,alligator gars)    Halecomorphi(1 living species:bowfin)     Teleostei(>32,000 living species)           Anatomy and physiology Further information:Fish anatomyandFish physiology  Organs: 1.Liver, 2.Gas bladder, 3.Roe, 4.Pyloric caeca, 5.Stomach, 6.Intestine Respiration See also:Aquatic respiration Gills  Tunagills inside the head. The fish head is oriented snout-downwards, with the view looking towards the mouth. Most fish exchange gases usinggillson either side of thepharynx. Gills consist of threadlike structures calledfilaments. Each filament contains acapillarynetwork that provides a largesurface areafor exchangingoxygenandcarbon dioxide. Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. In some fish, capillary blood flows in the opposite direction to the water, causingcountercurrent exchange. The gills push the oxygen-poor water out through openings in the sides of the pharynx. Some fish, likesharksandlampreys, possess multiple gill openings. However,bony fishhave a single gill opening on each side. This opening is hidden beneath a protective bony cover called anoperculum. Juvenilebichirshave external gills, a very primitive feature that they share with larvalamphibians. Air breathing Fish from multiple groups can live out of the water for extended periods.Amphibious fishsuch as themudskippercan live and move about on land for up to several days,[dubious–discuss]or live in stagnant or otherwise oxygen depleted water. Many such fish can breathe air via a variety of mechanisms. The skin ofanguillid eelsmay absorb oxygen directly. Thebuccal cavityof theelectric eelmay breathe air. Catfish of the familiesLoricariidae,Callichthyidae, andScoloplacidaeabsorb air through their digestive tracts.[38]Lungfish, with the exception of theAustralian lungfish, andbichirshave paired lungs similar to those oftetrapodsand must surface to gulp fresh air through the mouth and pass spent air out through the gills.Garandbowfinhave a vascularized swim bladder that functions in the same way.Loaches,trahiras, and manycatfishbreathe by passing air through the gut. Mudskippers breathe by absorbing oxygen across the skin (similar to frogs). A number of fish have evolved so-called accessory breathing organs that extract oxygen from the air. Labyrinth fish (such asgouramisandbettas) have alabyrinth organabove the gills that performs this function. A few other fish have structures resembling labyrinth organs in form and function, most notablysnakeheads,pikeheads, and theClariidaecatfish family. Breathing air is primarily of use to fish that inhabit shallow, seasonally variable waters where the water's oxygen concentration may seasonally decline. Fish dependent solely on dissolved oxygen, such as perch andcichlids, quickly suffocate, while air-breathers survive for much longer, in some cases in water that is little more than wet mud. At the most extreme, some air-breathing fish are able to survive in damp burrows for weeks without water, entering a state ofaestivation(summertime hibernation) until water returns. Air breathing fish can be divided into obligate air breathers and facultative air breathers. Obligate air breathers, such as theAfrican lungfish,mustbreathe air periodically or they suffocate. Facultative air breathers, such as the catfishHypostomus plecostomus, only breathe air if they need to and will otherwise rely on their gills for oxygen. Most air breathing fish are facultative air breathers that avoid the energetic cost of rising to the surface and the fitness cost of exposure to surface predators.[38] Circulation  Didactic modelof a fish heart Fish have aclosed-loop circulatory system. Theheartpumps the blood in a single loop throughout the body. In most fish, the heart consists of four parts, including two chambers and an entrance and exit.[39]The first part is thesinus venosus, a thin-walled sac that collects blood from the fish'sveinsbefore allowing it to flow to the second part, theatrium, which is a large muscular chamber. The atrium serves as a one-way antechamber, sends blood to the third part,ventricle. The ventricle is another thick-walled, muscular chamber and it pumps the blood, first to the fourth part,bulbus arteriosus, a large tube, and then out of the heart. The bulbus arteriosus connects to theaorta, through which blood flows to the gills for oxygenation. Digestion Jaws allow fish to eat a wide variety of food, including plants and other organisms. Fish ingest food through the mouth and break it down in theesophagus. In the stomach, food is further digested and, in many fish, processed in finger-shaped pouches calledpyloric caeca, which secrete digestiveenzymesand absorb nutrients. Organs such as theliverandpancreasadd enzymes and various chemicals as the food moves through the digestive tract. The intestine completes the process of digestion and nutrient absorption. Excretion As with many aquatic animals, most fish release their nitrogenous wastes asammonia. Some of the wastesdiffusethrough the gills. Blood wastes arefilteredby thekidneys. Saltwater fish tend to lose water because ofosmosis. Their kidneys return water to the body. The reverse happens infreshwater fish: they tend to gain water osmotically. Their kidneys produce dilute urine for excretion. Some fish have specially adapted kidneys that vary in function, allowing them to move from freshwater to saltwater. Scales Main article:Fish scale The scales of fish originate from themesoderm(skin); they may be similar in structure to teeth. Sensory and nervous system  Dorsal view of the brain of therainbow trout Central nervous system Fish typically have quite small brains relative to body size compared with other vertebrates, typically one-fifteenth the brain mass of a similarly sized bird or mammal.[40]However, some fish have relatively large brains, most notablymormyridsandsharks, which have brains about as massive relative to body weight as birds andmarsupials.[41] Fish brains are divided into several regions. At the front are theolfactory lobes, a pair of structures that receive and process signals from thenostrilsvia the twoolfactory nerves.[40]The olfactory lobes are very large in fish that hunt primarily by smell, such as hagfish, sharks, and catfish. Behind the olfactory lobes is the two-lobedtelencephalon, the structural equivalent to thecerebruminhigher vertebrates. In fish the telencephalon is concerned mostly witholfaction.[40]Together these structures form the forebrain. Connecting the forebrain to the midbrain is thediencephalon(in the diagram, this structure is below the optic lobes and consequently not visible). The diencephalon performs functions associated withhormonesandhomeostasis.[40]Thepineal bodylies just above the diencephalon. This structure detects light, maintainscircadianrhythms, and controls color changes.[40] Themidbrain(or mesencephalon) contains the twooptic lobes. These are very large in species that hunt by sight, such asrainbow troutandcichlids.[40] The hindbrain (ormetencephalon) is particularly involved in swimming and balance.[40]The cerebellum is a single-lobed structure that is typically the biggest part of the brain.[40]Hagfish andlampreyshave relatively small cerebellae, while themormyridcerebellum is massive and apparently involved in theirelectrical sense.[40] The brain stem (ormyelencephalon) is the brain's posterior.[40]As well as controlling some muscles and body organs, in bony fish at least, the brain stem governsrespirationandosmoregulation.[40] Sense organs Main article:Sensory systems in fish Most fish possess highly developed sense organs. Nearly all daylight fish have color vision that is at least as good as a human's (seevision in fishes). Many fish also have chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears, many fish may not hear very well. Most fish have sensitive receptors that form thelateral line system, which detects gentle currents and vibrations, and senses the motion of nearby fish and prey.[42]The sense information obtained from the lateral line system can be considered both a sense oftouchandhearing.Blind cave fishnavigate almost entirely through the sensations from their lateral line system.[43]Some fish, such as catfish and sharks, have theampullae of Lorenzini,electroreceptorsthat detect weak electric currents on the order of millivolt.[44]Other fish, like the South American electric fishesGymnotiformes, can produce weak electric currents, which they use in navigation and social communication. Fish orient themselves using landmarks and may use mental maps based on multiple landmarks or symbols. Fish behavior in mazes reveals that they possess spatial memory and visual discrimination.[45] Vision Main article:Vision in fishes Visionis an importantsensory systemfor most species of fish. Fish eyes are similar to those ofterrestrialvertebrateslikebirdsand mammals, but have a moresphericallens. Theirretinasgenerally have bothrodsandcones(forscotopicandphotopic vision), and most species havecolour vision. Some fish can seeultravioletand some can seepolarized light. Amongstjawless fish, thelampreyhas well-developed eyes, while thehagfishhas only primitiveeyespots.[46]Fish vision showsadaptationto their visual environment, for exampledeep sea fisheshave eyes suited to the dark environment. Hearing See also:Hearing in fish Hearingis an important sensory system for most species of fish. Fish sense sound using theirlateral linesand theirears. Cognition Further information:Fish intelligence New research has expanded preconceptions about the cognitive capacities of fish. For example,manta rayshave exhibited behavior linked toself-awarenessinmirror testcases. Placed in front of a mirror, individual rays engaged in contingency testing, that is, repetitive behavior aiming to check whether their reflection's behavior mimics their body movement.[47] Wrasseshave also passed the mirror test in a 2018 scientific study.[48][49] Cases of tool use have also been noticed, notably in theChoerodonfamily, inarcherfishandAtlantic cod.[50] Capacity for pain Further information:Pain in fish Experiments done by William Tavolga provide evidence that fish havepainand fear responses. For instance, in Tavolga's experiments,toadfishgrunted when electrically shocked and over time they came to grunt at the mere sight of an electrode.[51] In 2003, Scottish scientists at theUniversity of Edinburghand the Roslin Institute concluded that rainbow trout exhibit behaviors often associated withpainin other animals.Beevenomandacetic acidinjected into the lips resulted in fish rocking their bodies and rubbing their lips along the sides and floors of their tanks, which the researchers concluded were attempts to relieve pain, similar to what mammals would do.[52][53]Neurons fired in a pattern resembling human neuronal patterns.[53] Professor James D. Rose of theUniversity of Wyomingclaimed the study was flawed since it did not provide proof that fish possess "conscious awareness, particularly a kind of awareness that is meaningfully like ours".[54]Rose argues that since fish brains are so different from human brains, fish are probably not conscious in the manner humans are, so that reactions similar to human reactions to pain instead have other causes. Rose had published a study a year earlier arguing that fish cannot feel pain because their brains lack aneocortex.[55]However, animal behavioristTemple Grandinargues that fish could still have consciousness without a neocortex because "different species can use different brain structures and systems to handle the same functions."[53] Animal welfare advocates raise concerns about the possiblesufferingof fish caused by angling. Some countries, such as Germany, have banned specific types of fishing, and the BritishRSPCAnow formally prosecutes individuals who are cruel to fish.[56] Emotion In 2019, scientists have shown that members of themonogamousspeciesAmatitlania siquiaexhibit pessimistic behavior when they are prevented from being with their partner.[57] Muscular system Main article:Fish locomotion  The anatomy ofLampanyctodes hectoris(1)operculum (gill cover), (2)lateral line, (3)dorsal fin, (4)fat fin, (5)caudal peduncle, (6)caudal fin, (7)anal fin, (8)photophores, (9)pelvic fins (paired), (10)pectoral fins (paired)  Swim bladder of a rudd (Scardinius erythrophthalmus) Most fish move by alternately contracting paired sets of muscles on either side of the backbone. These contractions form S-shaped curves that move down the body. As each curve reaches the back fin, backward force is applied to the water, and in conjunction with the fins, moves the fish forward. The fish's fins function like an airplane's flaps. Fins also increase the tail's surface area, increasing speed. The streamlined body of the fish decreases the amount of friction from the water. Since body tissue is denser than water, fish must compensate for the difference or they will sink. Many bony fish have an internal organ called aswim bladderthat adjusts their buoyancy through manipulation of gases. Endothermy Although most fish are exclusivelyectothermic, there are exceptions. The only known bony fishes (infraclassTeleostei) that exhibitendothermyare in the suborderScombroidei– which includes thebillfishes, tunas, and thebutterfly kingfish, abasalspecies of mackerel[58]– and also theopah. The opah, alampriform, was demonstrated in 2015 to utilize "whole-body endothermy", generating heat with its swimming muscles to warm its body while countercurrent exchange (as in respiration) minimizes heat loss.[59]It is able to actively hunt prey such as squid and swim for long distances due to the ability to warm its entire body, including its heart,[60]which is a trait typically found in only mammals and birds (in the form ofhomeothermy). In the cartilaginous fishes (classChondrichthyes), sharks of the familiesLamnidae(porbeagle, mackerel, salmon, and great white sharks) andAlopiidae(thresher sharks) exhibit endothermy. The degree of endothermy varies from the billfishes, which warm only their eyes and brain, to thebluefin tunaand theporbeagle shark, which maintain body temperatures in excess of 20°C (68°F) above ambient water temperatures.[58] Endothermy, though metabolically costly, is thought to provide advantages such as increased muscle strength, higher rates of centralnervous systemprocessing, and higher rates ofdigestion. Reproductive system Further information:Fish reproductionandSpawn (biology)  Ovary of fish (Corumbatá) Fish reproductive organs includetesticlesandovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused.[61]There may also be a range of secondary organs that increase reproductive fitness. In terms ofspermatogoniadistribution, the structure ofteleoststestes has two types: in the most common, spermatogonia occur all along theseminiferous tubules, while inatherinomorphfish they are confined to thedistalportion of these structures. Fish can present cystic or semi-cysticspermatogenesisin relation to the release phase of germ cells in cysts to the seminiferous tubuleslumen.[61] Fish ovaries may be of three types: gymnovarian, secondary gymnovarian or cystovarian. In the first type, theoocytesare released directly into thecoelomiccavity and then enter theostium, then through theoviductand are eliminated. Secondary gymnovarian ovaries shedovainto the coelom from which they go directly into the oviduct. In the third type, the oocytes are conveyed to the exterior through the oviduct.[62]Gymnovaries are the primitive condition found inlungfish,sturgeon, andbowfin. Cystovaries characterize most teleosts, where the ovary lumen has continuity with the oviduct.[61]Secondary gymnovaries are found insalmonidsand a few other teleosts. Oogoniadevelopment in teleosts fish varies according to the group, and the determination of oogenesis dynamics allows the understanding of maturation and fertilization processes. Changes in thenucleus, ooplasm, and the surrounding layers characterize the oocyte maturation process.[61] Postovulatoryfolliclesare structures formed after oocyte release; they do not haveendocrinefunction, present a wide irregular lumen, and are rapidly reabsorbed in a process involving theapoptosisof follicular cells. A degenerative process calledfollicular atresiareabsorbs vitellogenic oocytes not spawned. This process can also occur, but less frequently, in oocytes in other development stages.[61] Some fish, like theCalifornia sheephead, arehermaphrodites, having both testes and ovaries either at different phases in their life cycle or, as inhamlets, have them simultaneously. Over 97% of all known fish areoviparous,[63]that is, the eggs develop outside the mother's body. Examples of oviparous fish includesalmon,goldfish,cichlids,tuna, andeels. In the majority of these species, fertilisation takes place outside the mother's body, with the male and female fish shedding theirgametesinto the surrounding water. However, a few oviparous fish practice internal fertilization, with the male using some sort ofintromittent organto deliver sperm into the genital opening of the female, most notably the oviparous sharks, such as thehorn shark, and oviparous rays, such asskates. In these cases, the male is equipped with a pair of modifiedpelvic finsknown asclaspers. Marine fish can produce high numbers of eggs which are often released into the open water column. The eggs have an average diameter of 1 millimetre (0.04in).  Egg oflamprey  Egg ofcatshark(mermaids' purse)  Egg ofbullhead shark  Egg ofchimaera The newly hatched young of oviparous fish are calledlarvae. They are usually poorly formed, carry a largeyolk sac(for nourishment), and are very different in appearance from juvenile and adult specimens. The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termedmetamorphosis) to become juveniles. During this transition larvae must switch from their yolk sac to feeding onzooplanktonprey, a process which depends on typically inadequate zooplankton density, starving many larvae. Inovoviviparousfish the eggs develop inside the mother's body after internal fertilization but receive little or no nourishment directly from the mother, depending instead on theyolk. Each embryo develops in its own egg. Familiar examples of ovoviviparous fish includeguppies,angel sharks, andcoelacanths. Some species of fish areviviparous. In such species the mother retains the eggs and nourishes the embryos. Typically, viviparous fish have a structure analogous to theplacentaseen inmammalsconnecting the mother's blood supply with that of the embryo. Examples of viviparous fish include thesurf-perches,splitfins, andlemon shark. Some viviparous fish exhibitoophagy, in which the developing embryos eat other eggs produced by the mother. This has been observed primarily among sharks, such as theshortfin makoandporbeagle, but is known for a few bony fish as well, such as thehalfbeakNomorhamphus ebrardtii.[64]Intrauterine cannibalismis an even more unusual mode of vivipary, in which the largest embryos eat weaker and smaller siblings. This behavior is also most commonly found among sharks, such as thegrey nurse shark, but has also been reported forNomorhamphus ebrardtii.[64] Aquaristscommonly refer to ovoviviparous and viviparous fish aslivebearers. Acoustic communication See also:Acoustic communication in aquatic animals Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another. The production of sounds as a means of communication among fish is most often used in the context of feeding, aggression or courtship behaviour.[3]The sounds emitted can vary depending on the species and stimulus involved. Fish can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder.[65] Stridulatory  French grunts –Haemulon flavolineatum There are some species of fish that can produce sounds by rubbing or grinding their bones together. These noises produced by bone-on-bone interactions are known as 'stridulatory sounds'.[65] An example of this is seen inHaemulon flavolineatum, a species commonly referred to as the 'French grunt fish', as it produces a grunting noise by grinding its teeth together.[65]This behaviour is most pronounced when theH. flavolineatumis in distress situations.[65]The grunts produced by this species of fishes generate a frequency of approximately 700Hz, and last approximately 47 milliseconds.[65]TheH. flavolineatumdoes not emit sounds with frequencies greater than 1000Hz, and does not detect sounds that have frequencies greater than 1050Hz.[65] In a study conducted by Oliveira et al. (2014), the longsnout seahorse,Hippocampus reidi, was recorded producing two different categories of sounds; 'clicks' and 'growls'. The sounds emitted by theH. reidiare accomplished by rubbing their coronet bone across the grooved section of their neurocranium.[66]'Clicking' sounds were found to be primarily produced during courtship and feeding, and the frequencies of clicks were within the range of 50Hz-800Hz.[67]The frequencies were noted to be on the higher end of the range during spawning periods, when the female and male fishes were less than fifteen centimeters apart.[67]Growl sounds were produced when theH. reidiencountered stressful situations, such as handling by researchers.[67]The 'growl' sounds consist of a series of sound pulses and are emitted simultaneously with body vibrations.[67] Non-stridulatory  Oyster toadfish Some fish species create noise by engaging specialized muscles that contract and cause swimbladder vibrations. Oyster toadfishproduce loud grunting sounds by contracting muscles located along the sides of their swim bladder, known as sonic muscles[68]Female and male toadfishes emit short-duration grunts, often as a fright response.[69]In addition to short-duration grunts, male toadfishes produce "boat whistle calls".[70]These calls are longer in duration, lower in frequency, and are primarily used to attract mates.[70]The sounds emitted by theO. taohave frequency range of 140Hz to 260Hz.[70]The frequencies of the calls depend on the rate at which the sonic muscles contract.[71][68] The red drum,Sciaenops ocellatus, produces drumming sounds by vibrating its swimbladder.[72]Vibrations are caused by the rapid contraction of sonic muscles that surround the dorsal aspect of the swimbladder.[72]These vibrations result in repeated sounds with frequencies that range from 100 to >200Hz.[72]TheS. ocellatuscan produce different calls depending on the stimuli involved.[72]The sounds created in courtship situations are different from those made during distressing events such as predatorial attacks.[72]Unlike the males of theS. ocellatusspecies, the females of this species do not produce sounds and lack sound-producing (sonic) muscles.[72] Diseases Main article:Fish diseases and parasites Like other animals, fish suffer from diseases and parasites. To prevent disease they have a variety of defenses.Non-specificdefenses include the skin and scales, as well as the mucus layer secreted by theepidermisthat traps and inhibits the growth ofmicroorganisms. Ifpathogensbreach these defenses, fish can develop aninflammatory responsethat increases blood flow to the infected region and deliverswhite blood cellsthat attempt to destroy pathogens. Specific defenses respond to particular pathogens recognised by the fish's body, i.e., animmune response.[73]In recent years,vaccineshave become widely used in aquaculture and also with ornamental fish, for examplefurunculosisvaccines in farmedsalmonandkoi herpes virusinkoi.[74][75] Some species usecleaner fishto remove external parasites. The best known of these are thebluestreak cleaner wrassesof the genusLabroidesfound oncoral reefsin theIndianandPacificoceans. These small fish maintain so-called "cleaning stations" where other fish congregate and perform specific movements to attract the attention of the cleaners.[76]Cleaning behaviors have been observed in a number of fish groups, including an interesting case between two cichlids of the same genus,Etroplus maculatus, the cleaner, and the much largerEtroplus suratensis.[77] Immune system Immune organs vary by type of fish.[78]In thejawless fish(lampreys and hagfish), truelymphoidorgans are absent. These fish rely on regions oflymphoid tissuewithin other organs to produce immune cells. For example,erythrocytes,macrophagesandplasma cellsare produced in the anterior kidney (orpronephros) and some areas of the gut (wheregranulocytesmature.) They resemble primitivebone marrowin hagfish.Cartilaginous fish(sharks and rays) have a more advanced immune system. They have three specialized organs that are unique toChondrichthyes; the epigonal organs (lymphoid tissue similar to mammalian bone) that surround the gonads, theLeydig's organwithin the walls of their esophagus, and aspiral valvein their intestine. These organs house typical immune cells (granulocytes, lymphocytes and plasma cells). They also possess an identifiablethymusand a well-developedspleen(their most important immune organ) where variouslymphocytes, plasma cells and macrophages develop and are stored.Chondrosteanfish (sturgeons, paddlefish, and bichirs) possess a major site for the production of granulocytes within a mass that is associated with themeninges(membranes surrounding the central nervous system.) Their heart is frequently covered with tissue that contains lymphocytes,reticular cellsand a small number ofmacrophages. The chondrostean kidney is an importanthemopoieticorgan; where erythrocytes, granulocytes, lymphocytes and macrophages develop. Like chondrostean fish, the major immune tissues of bony fish (orteleostei) include the kidney (especially the anterior kidney), which houses many different immune cells.[79]In addition, teleost fish possess a thymus, spleen and scattered immune areas within mucosal tissues (e.g. in the skin, gills, gut and gonads). Much like the mammalian immune system, teleost erythrocytes, neutrophils and granulocytes are believed to reside in the spleen whereas lymphocytes are the major cell type found in the thymus.[80][81]In 2006, a lymphatic system similar to that in mammals was described in one species of teleost fish, thezebrafish. Although not confirmed as yet, this system presumably will be where naive (unstimulated)T cellsaccumulate while waiting to encounter anantigen.[82] B and T lymphocytes bearingimmunoglobulinsandT cell receptors, respectively, are found in all jawed fishes. Indeed, theadaptive immune systemas a wholeevolvedin an ancestor of all jawed vertebrates.[83] Conservation The 2006IUCNRed Listnames 1,173 fish species that are threatened with extinction.[84]Included are species such asAtlantic cod,[85]Devil's Hole pupfish,[86]coelacanths,[87]andgreat white sharks.[88]Because fish live underwater they are more difficult to study than terrestrial animals and plants, and information about fish populations is often lacking. However, freshwater fish seem particularly threatened because they often live in relatively small water bodies. For example, theDevil's Hole pupfishoccupies only a single 3 by 6 metres (10 by 20ft) pool.[89] Overfishing  Whale sharks, the largest species of fish, are classified asvulnerable. Main article:Overfishing Overfishing is a major threat to edible fish such as cod andtuna.[90][91]Overfishing eventually causespopulation(known asstock) collapse because the survivors cannot produce enough young to replace those removed. Suchcommercial extinctiondoes not mean that the species is extinct, merely that it can no longer sustain a fishery. One well-studied example of fishery collapse is thePacific sardineSadinops sagax caeruluesfishery off the California coast. From a 1937 peak of 790,000 long tons (800,000t) the catch steadily declined to only 24,000 long tons (24,000t) in 1968, after which the fishery was no longer economically viable.[92] The main tension betweenfisheries scienceand thefishing industryis that the two groups have different views on the resiliency of fisheries to intensive fishing. In places such as Scotland, Newfoundland, and Alaska the fishing industry is a major employer, so governments are predisposed to support it.[93][94]On the other hand, scientists and conservationists push for stringent protection, warning that many stocks could be wiped out within fifty years.[95][96] Habitat destruction See also:Environmental impact of fishing A key stress on both freshwater and marine ecosystems is habitat degradation includingwater pollution, the building of dams, removal of water for use by humans, and the introduction ofexoticspecies.[97]An example of a fish that has become endangered because of habitat change is thepallid sturgeon, a North American freshwater fish that lives in rivers damaged by human activity.[98] Exotic species Introduction ofnon-nativespecies has occurred in many habitats. One of the best studied examples is the introduction ofNile perchintoLake Victoriain the 1960s. Nile perch gradually exterminated the lake's 500endemiccichlidspecies. Some of them survive now in captive breeding programmes, but others are probably extinct.[99]Carp,snakeheads,[100]tilapia,European perch,brown trout,rainbow trout, andsea lampreysare other examples of fish that have caused problems by being introduced into alien environments. Importance to humans Economic Main articles:Fishing industry,Aquaculture, andFish farming  These fish-farming ponds were created as acooperativeproject in a rural village. Throughout history, humans have utilizedfish as a food source. Historically and today, most fishproteinhas come by means of catching wild fish. However, aquaculture, or fish farming, which has been practiced since about 3,500 BCE. in China,[101]is becoming increasingly important in many nations. Overall, about one-sixth of the world's protein is estimated to be provided by fish.[102]That proportion is considerably elevated in somedeveloping nationsand regions heavily dependent on the sea. In a similar manner, fish have been tied to trade.  Fish counter display at theOulu Market HallinOulu, Finland. Catching fish for the purpose of food or sport is known asfishing, while the organized effort by humans to catch fish is called afishery. Fisheries are a huge global business and provide income for millions of people.[102]The annual yield from all fisheries worldwide is about 154 million tons,[103]with popular species includingherring,cod,anchovy,tuna,flounder, andsalmon. However, the term fishery is broadly applied, and includes more organisms than just fish, such asmollusksandcrustaceans, which are often called "fish" when used as food. Recreation  ABengalifish vendor Main articles:Fishkeeping,Recreational fishing, andAngling Fishkeeping Fish have been recognized as a source of beauty for almost as long as used for food, appearing incave art, being raised asornamental fishin ponds, and displayed inaquariumsin homes, offices, or public settings. Recreational fishing Recreational fishingis fishing primarily for pleasure or competition; it can be contrasted withcommercial fishing, which is fishing for profit, orartisanal fishing, which is fishing primarily for food. The most common form of recreational fishing is done with arod,reel,line,hooks, and any one of a wide range ofbaits. Recreational fishing is particularly popular in North America and Europe and state, provincial, and federal government agencies actively management target fish species.[104][105]Angling is a method of fishing, specifically the practice of catching fish by means of an "angle" (hook). Anglers must select the right hook,castaccurately, and retrieve at the right speed while considering water and weather conditions, species, fish response, time of the day, and other factors. Culture Main article:Fish in culture  AvatarofVishnuas aMatsya Fish themes have symbolic significance in many religions. In ancientMesopotamia, fish offerings were made to the gods from the very earliest times.[106]Fish were also a major symbol ofEnki, the god of water.[106]Fish frequently appear as filling motifs incylinder sealsfrom theOld Babylonian(c.1830 BC –c.1531 BC) andNeo-Assyrian(911–609 BC) periods.[106]Starting during theKassite Period(c.1600 BC –c.1155 BC) and lasting until the earlyPersian Period(550–30 BC), healers and exorcists dressed in ritual garb resembling the bodies of fish.[106]During theSeleucid Period(312–63 BC), the legendary Babylonianculture heroOannes, described byBerossus, was said to have dressed in the skin of a fish.[106]Fish were sacred to the Syrian goddessAtargatis[107]and, during her festivals, only her priests were permitted to eat them.[107]  Theichthusis a Christian symbol of a fish signifying that the person who uses it is a Christian.[107][108] In theBook of Jonah, a work of Jewish literature probably written in the fourth century BC, the central figure, aprophetnamedJonah, is swallowed by a giant fish after being thrown overboard by the crew of the ship he is travelling on.[109][110][111]The fish later vomits Jonah out on shore after three days.[109][110][111]This book was later included as part of theHebrew Bible, or ChristianOld Testament,[112][113]and a version of the story it contains is summarized inSurah37:139-148 of theQuran.[114]Early Christiansused theichthys, a symbol of a fish, to represent Jesus,[107][108]because the Greek word for fish, ΙΧΘΥΣ Ichthys, could be used as an acronym for "Ίησοῦς Χριστός, Θεοῦ Υἱός, Σωτήρ" (Iesous Christos, Theou Huios, Soter), meaning "Jesus Christ, Son of God, Saviour".[107][108]Thegospelsalso refer to "fishers of men"[115]andfeeding the multitude. In thedhammaofBuddhism, the fish symbolize happiness as they have complete freedom of movement in the water. Often drawn in the form ofcarpwhich are regarded in the Orient as sacred on account of their elegant beauty, size and life-span. Among thedeitiessaid to take the form of a fish areIka-Roaof thePolynesians,Dagonof various ancientSemitic peoples, the shark-gods ofHawaiʻiandMatsyaof the Hindus. TheastrologicalsymbolPiscesis based on a constellation of thesame name, but there is also a second fish constellation in the night sky,Piscis Austrinus.[116] Fish feature prominently in art and literature, in movies such asFinding Nemoand books such asThe Old Man and the Sea. Large fish, particularly sharks, have frequently been the subject ofhorror moviesandthrillers, most notably the novelJaws, which spawned a series of films of thesame namethat in turn inspired similar films or parodies such asShark TaleandSnakehead Terror. Piranhas are shown in a similar light to sharks in films such asPiranha; however, contrary to popular belief, thered-bellied piranhais actually a generally timid scavenger species that is unlikely to harm humans.[117]Legends of half-human, half-fishmermaidshave featured in folklore, including the stories ofHans Christian Andersen. Terminology "Fish" or "fishes" Though often used interchangeably, in biology these words have different meanings.Fishis used as a singular noun, or as a plural to describe multiple individuals from a single species.Fishesis used to describe different species or species groups.[118][119][120]Thus a pond would be said to contain 120 fish if all were from a single species or 120 fishes if these included a mix of several species. The distinction is similar to that between people and peoples. "True fish" or "finfish" In biology, the termfishis most strictly used to describe any animal with abackbone,gillsthroughout life, and limbs (if any) in the shape offins.[23]Many types ofaquatic animalswith common names ending in "fish" are not fish in thissense; examples includeshellfish,cuttlefish,starfish,crayfishandjellyfish. In earlier times, even biologists did not make a distinction– sixteenth century natural historians classified alsoseals, whales,amphibians,crocodiles, evenhippopotamuses, as well as a host of aquatic invertebrates, as fish.[26] In fisheries, the termfishis used as a collective term, and includesmollusks,crustaceansand anyaquatic animalwhich is harvested.[121] The strict biological definition of a fish, above, is sometimes called atrue fish. True fish are also referred to asfinfishorfin fishto distinguish them from other aquatic life harvested in fisheries or aquaculture. "Shoal" or "school" Main article:Shoaling and schooling  Thesegoldband fusiliersareschoolingbecause their swimming is synchronised. An assemblage of fish merely using some localised resource such as food or nesting sites is known simply as anaggregation. When fish come together in an interactive, social grouping, then they may be forming either ashoalor aschooldepending on the degree of organisation. Ashoalis a loosely organised group where each fish swims and forages independently but is attracted to other members of the group and adjusts its behaviour, such as swimming speed, so that it remains close to the other members of the group.Schoolsof fish are much more tightly organised, synchronising their swimming so that all fish move at the same speed and in the same direction. Shoaling and schooling behaviour is believed to provide a variety of advantages.[122] Examples: Cichlids congregating atlekkingsites form anaggregation. Many minnows and characins formshoals. Anchovies, herrings and silversides are classic examples ofschoolingfish. The most common collective nouns for a group of fish in general are school and shoal. Both the words have evolved from the same common Dutch root 'schole' meaning a troop or crowd. While the words "school" and "shoal" have different meanings within biology, the distinctions are often ignored by non-specialists who treat the words assynonyms. Thus speakers ofBritish Englishcommonly use "shoal" to describe any grouping of fish, and speakers ofAmerican Englishcommonly use "school" just as loosely.[123]

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A singel butterflie. Butterfliesareinsectsin themacrolepidopterancladeRhopalocera from theorderLepidoptera, which also includesmoths. Adult butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. The group comprises the largesuperfamilyPapilionoidea, which contains at least one former group, the skippers (formerly the superfamily "Hesperioidea"), and the most recent analyses suggest it also contains the moth-butterflies (formerly the superfamily "Hedyloidea"). Butterfly fossils date to thePaleocene, about 56 million years ago. Butterflies Temporal range:Palaeocene-Present,56–0Ma PreꞒ Ꞓ O S D C P T J K Pg N Papilio machaonScientific classificationKingdom:AnimaliaPhylum:ArthropodaClass:InsectaOrder:LepidopteraSuborder:RhopaloceraSubgroups SuperfamilyHedyloidea: Hedylidae SuperfamilyPapilionoidea: Hesperiidae Lycaenidae Nymphalidae Papilionidae Pieridae Riodinidae Butterflies have a four-stage life cycle, as like most insects they undergocomplete metamorphosis. Winged adults lay eggs on the food plant on which theirlarvae, known ascaterpillars, will feed. The caterpillars grow, sometimes very rapidly, and when fully developed,pupatein achrysalis. Whenmetamorphosisis complete, the pupal skin splits, the adult insect climbs out, and after its wings have expanded and dried, it flies off. Some butterflies, especially in the tropics, have several generations in a year, while others have a single generation, and a few in cold locations may take several years to pass through their entire life cycle. Butterflies are oftenpolymorphic, and many species make use ofcamouflage,mimicry, andaposematismto evade their predators.[1]Some, like themonarchand thepainted lady,migrateover long distances. Many butterflies are attacked byparasitesorparasitoids, includingwasps,protozoans,flies, and other invertebrates, or arepreyed uponby other organisms. Some species are pests because in their larval stages they can damage domestic crops or trees; other species are agents ofpollinationof some plants. Larvae of a few butterflies (e.g.,harvesters) eat harmful insects, and a few are predators ofants, while others live asmutualistsin association with ants. Culturally, butterflies are a popular motif in the visual and literary arts. TheSmithsonian Institutionsays "butterflies are certainly one of the most appealing creatures in nature".[2] Contents Etymology  Possibly the original butter-fly.[3]A male brimstone (Gonepteryx rhamni) in flight TheOxford English Dictionaryderives the word straightforwardly fromOld Englishbutorflēoge, butter-fly; similar names inOld DutchandOld High Germanshow that the name is ancient, but modern Dutch and German use different words (vlinderandSchmetterling) and the common name often varies substantially between otherwise closely-related languages. A possible source of the name is the bright yellow male of the brimstone (Gonepteryx rhamni); another is that butterflies were on the wing in meadows during the spring and summer butter season while the grass was growing.[3][4] Paleontology Further information:Prehistoric Lepidoptera The earliestLepidopterafossils date to theTriassic-Jurassicboundary, around 200 million years ago.[5]Butterflies evolved from moths, so while the butterflies aremonophyletic(forming a singleclade), the moths are not. The oldest known butterfly isProtocoeliades kristensenifrom thePalaeoceneagedFur Formationof Denmark, approximately 55 million years old, which belongs to the familyHesperiidae(skippers).[6]Molecular clockestimates suggest that butterflies originated sometime in the mid-Cretaceous, but only significantly diversified during the Cenozoic.[7]The oldest American butterfly is theLate EoceneProdryas persephonefrom theFlorissant Fossil Beds,[8][9]approximately 34 million years old.[10] Butterfly Fossils  Prodryas persephone, aLate Eocenebutterfly from theFlorissant Fossil Beds, 1887 engraving  Lithopsyche antiqua, anEarly Oligocenebutterfly from the Bembridge Marls,Isle of Wight, 1889 engraving Taxonomy and phylogeny Further information:Taxonomy of the Lepidoptera Traditionally, butterflies have been divided into thesuperfamilyPapilionoideaexcluding the smaller groups of theHesperiidae(skippers) and the more moth-likeHedylidaeof America.Phylogeneticanalysis suggests that the traditional Papilionoidea isparaphyleticwith respect to the other two groups, so they should both be included within Papilionoidea, to form a single butterfly group, thereby synonymous with the cladeRhopalocera.[11][12] Butterfly familiesFamilyCommon nameCharacteristicsImageHedylidaeAmerican moth-butterfliesSmall, brown, likegeometrid moths;antennaenot clubbed; long slim abdomenHesperiidaeSkippersSmall, darting flight; clubs on antennae hooked backwardsLycaenidaeBlues, coppers, hairstreaksSmall, brightly coloured; often have false heads with eyespots and small tails resembling antennaeNymphalidaeBrush-footed or four-footed butterfliesUsually have reduced forelegs, so appear four-legged; often brightly colouredPapilionidaeSwallowtailsOften have 'tails' on wings; caterpillar generates foul taste withosmeteriumorgan; pupa supported by silk girdlePieridaeWhites and alliesMostly white, yellow or orange; some serious pests ofBrassica; pupa supported by silk girdleRiodinidaeMetalmarksOften have metallic spots on wings; often conspicuously coloured with black, orange and blue Biology  The wings of butterflies, hereAglais io, are covered with coloured scales. General description  Butterfly antennal shapes, mainly clubbed, unlike those of moths. Drawn by C. T. Bingham, 1905 Further information:Glossary of entomology termsandComparison of butterflies and moths  Unlike butterflies, most moths (likeLaothoe populi) fly by night and hide by day. Butterfly adults are characterized by their four scale-covered wings, which give the Lepidoptera their name (Ancient Greekλεπίς lepís, scale + πτερόν pterón, wing). These scales give butterfly wings their colour: they are pigmented withmelaninsthat give them blacks and browns, as well asuric acidderivatives andflavonesthat give them yellows, but many of the blues, greens, reds andiridescent coloursare created bystructural colorationproduced by the micro-structures of the scales and hairs.[13][14][15][16] As in all insects, the body is divided into three sections: the head,thorax, andabdomen. The thorax is composed of three segments, each with a pair of legs. In most families of butterfly the antennae are clubbed, unlike those ofmothswhich may be threadlike or feathery. The long proboscis can be coiled when not in use for sipping nectar from flowers.[17] Nearly all butterflies arediurnal, have relatively bright colours, and hold their wings vertically above their bodies when at rest, unlike the majority of moths which fly by night, are oftencrypticallycoloured (well camouflaged), and either hold their wings flat (touching the surface on which the moth is standing) or fold them closely over their bodies. Some day-flying moths, such as thehummingbird hawk-moth,[18]are exceptions to these rules.[17][19] Sexual dimorphisminAnthocharis cardamines Male Female Butterflylarvae,caterpillars, have a hard (sclerotised) head with strong mandibles used for cutting their food, most often leaves. They have cylindrical bodies, with ten segments to the abdomen, generally with short prolegs on segments 3–6 and 10; the three pairs of true legs on the thorax have five segments each.[17]Many are well camouflaged; others are aposematic with bright colours and bristly projections containing toxic chemicals obtained from their food plants. Thepupaor chrysalis, unlike that of moths, is not wrapped in a cocoon.[17] Many butterflies aresexually dimorphic. Most butterflies have theZW sex-determination systemwhere females are the heterogametic sex (ZW) and males homogametic (ZZ).[20] Distribution and migration See also: Lists of butterflies ofAustralia(Tasmania,Victoria),Britain,India,Menorca,North America,Taiwan, andTrinidad and Tobago Further information:Lepidoptera migration,Insect migration, andAnimal navigation Butterflies are distributed worldwide except Antarctica, totalling some 18,500 species.[21]Of these, 775 areNearctic; 7,700Neotropical; 1,575Palearctic; 3,650Afrotropical; and 4,800 are distributed across the combinedOrientalandAustralian/Oceaniaregions.[21]Themonarch butterflyis native to the Americas, but in the nineteenth century or before, spread across the world, and is now found in Australia, New Zealand, other parts of Oceania, and theIberian Peninsula. It is not clear how it dispersed; adults may have been blown by the wind or larvae or pupae may have been accidentally transported by humans, but the presence of suitable host plants in their new environment was a necessity for their successful establishment.[22]  Monarchmigration route  Overwintering monarchs cluster onoyameltrees nearAngangueo, Mexico. Many butterflies, such as thepainted lady, monarch, and severaldanainemigrate for long distances. These migrations take place over a number of generations and no single individual completes the whole trip. The eastern North American population of monarchs can travel thousands of miles south-west tooverwintering sites in Mexico. There is a reverse migration in the spring.[23][24]It has recently been shown that the British painted lady undertakes a 9,000-mile round trip in a series of steps by up to six successive generations, from tropical Africa to the Arctic Circle — almost double the length of the famous migrations undertaken by monarch.[25]Spectacular large-scale migrations associated with themonsoonare seen in peninsular India.[26]Migrations have been studied in more recent times using wing tags and also usingstable hydrogen isotopes.[27][28] Butterflies navigate using a time-compensated sun compass. They can see polarized light and therefore orient even in cloudy conditions. The polarized light near the ultraviolet spectrum appears to be particularly important.[29][30]Many migratory butterflies live in semi-arid areas where breeding seasons are short.[31]The life histories of their host plants also influence butterfly behaviour.[32] Life cycle  Life cycle of the monarch butterfly  Mating pair ofspotted fritillariesongreater pignut Butterflies in their adult stage can live from a week to nearly a year depending on the species. Many species have long larval life stages while others can remaindormantin their pupal or egg stages and thereby survive winters.[33]TheMelissa Arctic(Oeneis melissa) overwinters twice as a caterpillar.[34]Butterflies may have one or more broods per year. The number of generations per year varies fromtemperatetotropical regionswith tropical regions showing a trend towardsmultivoltinism.[35]  The male small skipper (Thymelicus sylvestris) haspheromone-releasing "sex brands" (dark line) on the upperside of its forewings. Courtshipis often aerial and often involvespheromones. Butterflies then land on the ground or on a perch to mate.[17]Copulation takes place tail-to-tail and may last from minutes to hours. Simple photoreceptor cells located at the genitals are important for this and other adult behaviours.[36]The male passes aspermatophoreto the female; to reduce sperm competition, he may cover her with his scent, or in some species such as the Apollos (Parnassius)plugs her genital openingto prevent her from mating again.[37] The vast majority of butterflies have a four-stage life cycle;egg,larva(caterpillar),pupa(chrysalis) andimago(adult). In the generaColias,Erebia,Euchloe, andParnassius, a small number of species are known that reproducesemi-parthenogenetically; when the female dies, a partially developed larva emerges from her abdomen.[38] Egg  Eggs of black-veined white (Aporia crataegi) onappleleaf  A butterfly laying eggs underneath the leaf Butterfly eggs are protected by a hard-ridged outer layer of shell, called thechorion. This is lined with a thin coating of wax which prevents the egg from drying out before the larva has had time to fully develop. Each egg contains a number of tiny funnel-shaped openings at one end, calledmicropyles; the purpose of these holes is to allow sperm to enter and fertilize the egg. Butterfly eggs vary greatly in size and shape between species, but are usually upright and finely sculptured. Some species lay eggs singly, others in batches. Many females produce between one hundred and two hundred eggs.[38] Butterfly eggs are fixed to a leaf with a special glue which hardens rapidly. As it hardens it contracts, deforming the shape of the egg. This glue is easily seen surrounding the base of every egg forming a meniscus. The nature of the glue has been little researched but in the case ofPieris brassicae, it begins as a pale yellow granular secretion containing acidophilic proteins. This is viscous and darkens when exposed to air, becoming a water-insoluble, rubbery material which soon sets solid.[39]Butterflies in the genusAgathymusdo not fix their eggs to a leaf, instead the newly laid eggs fall to the base of the plant.[40] Eggs are almost invariably laid on plants. Each species of butterfly has its own host plant range and while some species of butterfly are restricted to just one species of plant, others use a range of plant species, often including members of a common family.[41]In some species, such as thegreat spangled fritillary, the eggs are deposited close to but not on the food plant. This most likely happens when the egg overwinters before hatching and where the host plant loses its leaves in winter, as dovioletsin this example.[42] The egg stage lasts a few weeks in most butterflies, but eggs laid close to winter, especially in temperate regions, go through adiapause(resting) stage, and the hatching may take place only in spring.[43]Some temperate region butterflies, such as theCamberwell beauty, lay their eggs in the spring and have them hatch in the summer.[44] Caterpillar larva  Aposematiccaterpillar ofPapilio machaon, in threat pose Butterfly larvae, or caterpillars, consume plant leaves and spend practically all of their time searching for and eating food. Although most caterpillars are herbivorous, a few species arepredators:Spalgis epiuseatsscale insects,[45]while lycaenids such asLiphyra brassolisaremyrmecophilous, eating ant larvae.[46]  Mutualism: ant tending alycaenidcaterpillar,Catapaecilma major Some larvae, especially those of theLycaenidae, formmutual associationswith ants. They communicate with the ants using vibrations that are transmitted through thesubstrateas well as using chemical signals.[47][48]The ants provide some degree of protection to these larvae and they in turn gatherhoneydew secretions.Large blue(Phengaris arion) caterpillars trickMyrmicaants into taking them back to theant colonywhere they feed on the ant eggs and larvae in a parasitic relationship.[49]  Crypticcountershadedcaterpillar of a hawkmoth,Ceratomia amyntor Caterpillars mature through a series of developmental stages known asinstars. Near the end of each stage, the larva undergoes a process calledapolysis, mediated by the release of a series ofneurohormones. During this phase, thecuticle, a tough outer layer made of a mixture ofchitinand specializedproteins, is released from the softerepidermisbeneath, and the epidermis begins to form a new cuticle. At the end of each instar, the larvamoults, the old cuticle splits and the new cuticle expands, rapidly hardening and developing pigment.[50]Development of butterfly wing patterns begins by the last larval instar. Caterpillars have short antennae and severalsimple eyes. Themouthpartsare adapted for chewing with powerful mandibles and a pair of maxillae, each with a segmented palp. Adjoining these is the labium-hypopharynx which houses a tubular spinneret which is able to extrude silk.[13]Caterpillars such as those in the genusCalpodes(family Hesperiidae) have a specialized tracheal system on the 8th segment that function as a primitive lung.[51]Butterfly caterpillars have three pairs of true legs on the thoracic segments and up to six pairs ofprolegsarising from the abdominal segments. These prolegs have rings of tiny hooks called crochets that are engaged hydrostatically and help the caterpillar grip the substrate.[52]The epidermis bears tufts ofsetae, the position and number of which help in identifying the species. There is also decoration in the form of hairs, wart-like protuberances, horn-like protuberances and spines. Internally, most of the body cavity is taken up by the gut, but there may also be large silk glands, and special glands which secrete distasteful or toxic substances. The developing wings are present in later stage instars and thegonadsstart development in the egg stage.[13] Pupa  Chrysalisofgulf fritillary When the larva is fully grown, hormones such asprothoracicotropic hormone(PTTH) are produced. At this point the larva stops feeding, and begins "wandering" in the quest for a suitable pupation site, often the underside of a leaf or other concealed location. There it spins a button of silk which it uses to fasten its body to the surface and moults for a final time. While some caterpillars spin acocoonto protect the pupa, most species do not. The naked pupa, often known as a chrysalis, usually hangs head down from the cremaster, a spiny pad at the posterior end, but in some species a silken girdle may be spun to keep the pupa in a head-up position.[38]Most of the tissues and cells of the larva are broken down inside the pupa, as the constituent material is rebuilt into the imago. The structure of the transforming insect is visible from the exterior, with the wings folded flat on the ventral surface and the two halves of the proboscis, with the antennae and the legs between them.[13] The pupal transformation into a butterfly throughmetamorphosishas held great appeal to mankind. To transform from the miniature wings visible on the outside of the pupa into large structures usable for flight, the pupal wings undergo rapid mitosis and absorb a great deal of nutrients. If one wing is surgically removed early on, the other three will grow to a larger size. In the pupa, the wing forms a structure that becomes compressed from top to bottom and pleated from proximal to distal ends as it grows, so that it can rapidly be unfolded to its full adult size. Several boundaries seen in the adult colour pattern are marked by changes in the expression of particular transcription factors in the early pupa.[53] Adult  An adultParthenos sylviabutterfly The reproductive stage of the insect is the winged adult orimago. The surface of both butterflies and moths is covered by scales, each of which is an outgrowth from a singleepidermalcell. The head is small and dominated by the two largecompound eyes. These are capable of distinguishing flower shapes or motion but cannot view distant objects clearly. Colour perception is good, especially in some species in the blue/violet range. Theantennaeare composed of many segments and have clubbed tips (unlike moths that have tapering or feathery antennae). The sensory receptors are concentrated in the tips and can detect odours. Taste receptors are located on the palps and on the feet. The mouthparts are adapted to sucking and themandiblesare usually reduced in size or absent. The first maxillae are elongated into a tubularprobosciswhich is curled up at rest and expanded when needed to feed. The first and second maxillae bear palps which function as sensory organs. Some species have a reduced proboscis or maxillary palps and do not feed as adults.[13] ManyHeliconiusbutterflies also use their proboscis to feed on pollen;[54]in these species only 20% of the amino acids used in reproduction come from larval feeding, which allow them to develop more quickly as caterpillars, and gives them a longer lifespan of several months as adults.[55] The thorax of the butterfly is devoted to locomotion. Each of the three thoracic segments has two legs (amongnymphalids, the first pair is reduced and the insects walk on four legs). The second and third segments of the thorax bear the wings. The leading edges of the forewings have thick veins to strengthen them, and the hindwings are smaller and more rounded and have fewer stiffening veins. The forewings and hindwings are not hooked together (as they are in moths) but are coordinated by the friction of their overlapping parts. The front two segments have a pair ofspiracleswhich are used in respiration.[13] The abdomen consists of ten segments and contains the gut and genital organs. The front eight segments have spiracles and the terminal segment is modified for reproduction. The male has a pair of clasping organs attached to a ring structure, and during copulation, a tubular structure is extruded and inserted into the female's vagina. Aspermatophoreis deposited in the female, following which the sperm make their way to a seminal receptacle where they are stored for later use. In both sexes, the genitalia are adorned with various spines, teeth, scales and bristles, which act to prevent the butterfly from mating with an insect of another species.[13]After it emerges from its pupal stage, a butterfly cannot fly until the wings are unfolded. A newly emerged butterfly needs to spend some time inflating its wings withhemolymphand letting them dry, during which time it is extremely vulnerable to predators.[56] Pattern formation The colorful patterns on many butterfly wings tell potential predators that they are toxic. Hence, the genetic basis of wingpattern formationcan illuminate both theevolutionof butterflies as well as theirdevelopmental biology. The color of butterfly wings is derived from tiny structures called scales, each of which have their ownpigments. InHeliconiusbutterflies, there are three types of scales: yellow/white, black, and red/orange/brown scales. Some mechanism of wing pattern formation are now being solved using genetic techniques. For instance, agenecalledcortexdetermines the color of scales: deletingcortexturned black and red scales yellow. Mutations, e.g.transposon insertionsof the non-coding DNA around thecortexgene can turn a black-winged butterfly into a butterfly with a yellow wing band.[57] Behaviour  AnAustralian painted ladyfeeding on a flowering shrub Butterflies feed primarily onnectarfrom flowers. Some also derive nourishment frompollen,[58]tree sap, rotting fruit, dung, decaying flesh, and dissolved minerals in wet sand or dirt. Butterflies are important as pollinators for some species of plants. In general, they do not carry as much pollen load asbees, but they are capable of moving pollen over greater distances.[59]Flower constancyhas been observed for at least one species of butterfly.[60] Adult butterflies consume only liquids, ingested through the proboscis. They sip water from damp patches for hydration and feed on nectar from flowers, from which they obtain sugars for energy, andsodiumand other minerals vital for reproduction. Several species of butterflies need more sodium than that provided by nectar and are attracted by sodium in salt; they sometimes land on people, attracted by the salt in human sweat. Some butterflies also visit dung and scavenge rotting fruit or carcasses to obtain minerals and nutrients. In many species, thismud-puddlingbehaviour is restricted to the males, and studies have suggested that the nutrients collected may be provided as anuptial gift, along with the spermatophore, during mating.[61] Inhilltopping, males of some species seek hilltops and ridge tops, which they patrol in search for females. Since it usually occurs in species with low population density, it is assumed these landscape points are used as meeting places to find mates.[62] Butterflies use their antennae to sense the air for wind and scents. The antennae come in various shapes and colours; the hesperiids have a pointed angle or hook to the antennae, while most other families show knobbed antennae. The antennae are richly covered with sensory organs known assensillae. A butterfly's sense of taste is coordinated by chemoreceptors on thetarsi, or feet, which work only on contact, and are used to determine whether an egg-laying insect's offspring will be able to feed on a leaf before eggs are laid on it.[63]Many butterflies use chemical signals,pheromones; some have specialized scent scales (androconia) or other structures (coremataor "hair pencils" in the Danaidae).[64]Vision is well developed in butterflies and most species are sensitive to the ultraviolet spectrum. Many species show sexual dimorphism in the patterns of UV reflective patches.[65]Colour vision may be widespread but has been demonstrated in only a few species.[66][67]Some butterflies have organs of hearing and some species makestridulatoryand clicking sounds.[68]  Heteronympha meropetaking off Many species of butterfly maintain territories and actively chase other species or individuals that may stray into them. Some species will bask or perch on chosen perches. The flight styles of butterflies are often characteristic and some species have courtship flight displays. Butterflies can only fly when their temperature is above 27°C (81°F); when it is cool, they can position themselves to expose the underside of the wings to the sunlight to heat themselves up. If their body temperature reaches 40°C (104°F), they can orientate themselves with the folded wings edgewise to the sun.[69]Basking is an activity which is more common in the cooler hours of the morning. Some species have evolved dark wingbases to help in gathering more heat and this is especially evident in alpine forms.[70] As in many other insects, theliftgenerated by butterflies is more than can be accounted for by steady-state, non-transitoryaerodynamics. Studies usingVanessa atalantain awind tunnelshow that they use a wide variety of aerodynamic mechanisms to generate force. These includewake capture,vorticesat the wing edge, rotational mechanisms and theWeis-Fogh'clap-and-fling' mechanism. Butterflies are able to change from one mode to another rapidly.[71] Ecology  Braconidparasitoidalwasp (Apantelesspecies) cocoons attached to lime butterfly (Papilio demoleus) caterpillar Parasitoids, predators, and pathogens Butterflies are threatened in their early stages byparasitoidsand in all stages by predators, diseases and environmental factors.Braconidand other parasitic wasps lay their eggs in lepidopteran eggs or larvae and the wasps' parasitoid larvae devour their hosts, usually pupating inside or outside the desiccated husk. Most wasps are very specific about their host species and some have been used as biological controls of pest butterflies like thelarge white butterfly.[72]When thesmall cabbage whitewas accidentally introduced to New Zealand, it had no natural enemies. In order to control it, some pupae that had been parasitised by a chalcid wasp were imported, and natural control was thus regained.[73]Some flies lay their eggs on the outside of caterpillars and the newly hatched fly larvae bore their way through the skin and feed in a similar way to the parasitoid wasp larvae.[74]Predators of butterflies include ants, spiders, wasps, and birds.[75] Caterpillars are also affected by a range of bacterial, viral and fungal diseases, and only a small percentage of the butterfly eggs laid ever reach adulthood.[74]The bacteriumBacillus thuringiensishas been used in sprays to reduce damage to crops by the caterpillars of the large white butterfly, and theentomopathogenic fungusBeauveria bassianahas proved effective for the same purpose.[76] Endangered species Queen Alexandra's birdwingis the largest butterfly in the world. The species isendangered, and is one of only three insects (the other two being butterflies as well) to be listed onAppendix IofCITES, making international trade illegal.[77] Black grass-dart butterfly(Ocybadistes knightorum)is a butterfly of the familyHesperiidae. It is endemic toNew South Wales. It has a very limited distribution in theBoambeearea. Defences  Heliconiuswarns off predators withMüllerian mimicry.[78] Further information:Defense in insects,Anti-predator adaptation,Mimicry, andSeasonal polyphenism Butterflies protect themselves from predators by a variety of means.  Giant swallowtailcaterpillar everting itsosmeteriumin defence; it is alsomimetic, resembling a bird dropping. Chemical defences are widespread and are mostly based on chemicals of plant origin. In many cases the plants themselves evolved these toxic substances asprotectionagainst herbivores. Butterflies have evolved mechanisms to sequester these plant toxins and use them instead in their own defence.[79]These defence mechanisms are effective only if they are well advertised; this has led to the evolution of bright colours in unpalatable butterflies (aposematism). This signal is commonlymimickedby other butterflies, usually only females. ABatesian mimicimitates another species to enjoy the protection of that species' aposematism.[80]Thecommon Mormonof India has female morphs which imitate the unpalatable red-bodied swallowtails, thecommon roseand thecrimson rose.[81]Müllerian mimicryoccurs when aposematic species evolve to resemble each other, presumably to reduce predator sampling rates;Heliconiusbutterflies from the Americas are a good example.[80]  Eyespots ofspeckled wood(Pararge aegeria) distract predators from attacking the head. This insect can still fly with a damaged left hindwing. Camouflageis found in many butterflies. Some like the oakleaf butterfly andautumn leafare remarkable imitations of leaves.[82]As caterpillars, many defend themselves by freezing and appearing like sticks or branches.[83]Others havedeimaticbehaviours, such as rearing up and waving their front ends which are marked with eyespots as if they were snakes.[84]Some papilionid caterpillars such as the giant swallowtail (Papilio cresphontes) resemble bird droppings so as to be passed over by predators.[85]Some caterpillars have hairs and bristly structures that provide protection while others are gregarious and form dense aggregations.[80]Some species aremyrmecophiles, formingmutualistic associationswithantsand gaining their protection.[86]Behavioural defences include perching and angling the wings to reduce shadow and avoid being conspicuous. Some femaleNymphalidbutterflies guard their eggs from parasitoidalwasps.[87] The Lycaenidae have a false head consisting of eyespots and small tails (false antennae) to deflect attack from the more vital head region. These may also cause ambush predators such as spiders to approach from the wrong end, enabling the butterflies to detect attacks promptly.[88][89]Many butterflies haveeyespotson the wings; these too may deflect attacks, or may serve to attract mates.[53][90] Auditory defences can also be used, which in the case of thegrizzled skipperrefers to vibrations generated by the butterfly upon expanding its wings in an attempt to communicate with ant predators.[91] Many tropical butterflies haveseasonal formsfor dry and wet seasons.[92][93]These are switched by the hormoneecdysone.[94]The dry-season forms are usually more cryptic, perhaps offering better camouflage when vegetation is scarce. Dark colours in wet-season forms may help to absorb solar radiation.[95][96][90] Butterflies without defences such as toxins or mimicry protect themselves through a flight that is more bumpy and unpredictable than in other species. It is assumed this behavior makes it more difficult for predators to catch them, and is caused by theturbulencecreated by the small whirlpools formed by the wings during flight.[97] Declining numbers Declining butterfly populations have been noticed in many areas of the world, and this phenomenon is consistent with therapidly decreasing insect populations around the world. At least in the Western United States, this collapse in the number of most species of butterflies has been determined to be driven byglobal climate change, specifically, by warmer autumns.[98][99] In culture  Ancient Egyptianrelief sculpture,26th dynasty,Thebes. c. 664–525 BC In art and literature  Butterfly and Chinesewisteria, by Xü Xi. EarlySong Dynasty, c. 970  A butterfly in the coat of arms ofPerho Butterflies have appeared in art from 3500 years ago inancient Egypt.[100]In the ancientMesoamericancity ofTeotihuacan, the brilliantly coloured image of the butterfly was carved into many temples, buildings, jewellery, and emblazoned onincense burners. The butterfly was sometimes depicted with the maw of ajaguar, and some species were considered to be the reincarnations of the souls of dead warriors. The close association of butterflies with fire and warfare persisted into theAztec civilisation; evidence of similar jaguar-butterfly images has been found among theZapotecandMaya civilisations.[101] Butterflies are widely used in objects of art and jewellery: mounted in frames, embedded in resin, displayed in bottles, laminated in paper, and used in some mixed media artworks and furnishings.[102]TheNorwegiannaturalistKjell Sandvedcompiled a photographicButterfly Alphabetcontaining all 26 letters and the numerals 0 to 9 from the wings of butterflies.[103]  Alicemeets thecaterpillar. Illustration by SirJohn TennielinLewis Carroll'sAlice in Wonderland, c. 1865 SirJohn Tennieldrew a famous illustration ofAlicemeeting acaterpillarforLewis Carroll'sAlice in Wonderland, c. 1865. The caterpillar is seated on a toadstool and is smoking ahookah; the image can be read as showing either the forelegs of the larva, or as suggesting a face with protruding nose and chin.[3]Eric Carle's children's bookThe Very Hungry Caterpillarportrays the larva as an extraordinarily hungry animal, while also teaching children how to count (to five) and the days of the week.[3] A butterfly appeared in one ofRudyard Kipling'sJust So Stories, "The Butterfly that Stamped".[104] One of the most popular, and most often recorded, songs bySweden's eighteenth-century bard,Carl Michael Bellman, is "Fjäriln vingad syns på Haga" (The butterfly wingèd is seen in Haga), one of hisFredman's Songs.[105] Madam Butterflyis a 1904operabyGiacomo Pucciniabout a romantic young Japanese bride who is deserted by her American officer husband soon after they are married. It was based onJohn Luther Long's short story written in 1898.[106] In mythology and folklore  Der Schmetterlingsjäger(The butterfly hunter) painting byCarl Spitzweg, 1840 According toLafcadio Hearn, a butterfly was seen in Japan as the personification of a person's soul; whether they be living, dying, or already dead. One Japanese superstition says that if a butterfly enters your guest room and perches behind the bamboo screen, the person whom you most love is coming to see you. Large numbers of butterflies are viewed as badomens. WhenTaira no Masakadowas secretly preparing for his famous revolt, there appeared inKyotoso vast a swarm of butterflies that the people were frightened—thinking the apparition to be a portent of coming evil.[107]  A serving tray decorated with butterfly wings Diderot'sEncyclopédiecites butterflies as a symbol for the soul. A Roman sculpture depicts a butterfly exiting the mouth of a dead man, representing the Roman belief that the soul leaves through the mouth.[108]In line with this, the ancient Greek word for "butterfly" is ψυχή (psȳchē), which primarily means "soul" or "mind".[109]According toMircea Eliade, some of theNagasofManipurclaim ancestry from a butterfly.[110]In some cultures, butterflies symboliserebirth.[111]The butterfly is a symbol of beingtransgender, because of the transformation from caterpillar to winged adult.[112]In the English county ofDevon, people once hurried to kill the first butterfly of the year, to avoid a year of bad luck.[113]In the Philippines, a lingering black or dark butterfly or moth in the house is taken to mean an impending or recent death in the family.[114]Several American states have chosen anofficial state butterfly.[115] Collecting, recording, and rearing  Nōrobe Japan 1700s. Silk embroidered with silk thread and stenciled with gold foil "Collecting" means preserving dead specimens, not keeping butterflies as pets.[116][117]Collecting butterflies was once a popular hobby; it has now largely been replaced by photography, recording, and rearing butterflies for release into the wild.[3][dubious–discuss][full citation needed]The zoological illustratorFrederick William Frohawksucceeded in rearing all the butterfly species found in Britain, at a rate of four per year, to enable him to draw every stage of each species. He published the results in the folio sized handbookThe Natural History of British Butterfliesin 1924.[3] Butterflies andmothscan be reared for recreation or for release.[118] In technology Further information:Biomimetics Study of thestructural colorationof the wing scales of swallowtail butterflies has led to the development of more efficientlight-emitting diodes,[119]and is inspiringnanotechnologyresearch to produce paints that do not use toxic pigments and the development of new display technologies.[120]

Butterfliesareinsectsin themacrolepidopterancladeRhopalocera from theorderLepidoptera, which also includesmoths. Adult butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. The group comprises the largesuperfamilyPapilionoidea, which contains at least one former group, the skippers (formerly the superfamily "Hesperioidea"), and the most recent analyses suggest it also contains the moth-butterflies (formerly the superfamily "Hedyloidea"). Butterfly fossils date to thePaleocene, about 56 million years ago. Butterflies Temporal range:Palaeocene-Present,56–0Ma PreꞒ Ꞓ O S D C P T J K Pg N Papilio machaonScientific classificationKingdom:AnimaliaPhylum:ArthropodaClass:InsectaOrder:LepidopteraSuborder:RhopaloceraSubgroups SuperfamilyHedyloidea: Hedylidae SuperfamilyPapilionoidea: Hesperiidae Lycaenidae Nymphalidae Papilionidae Pieridae Riodinidae Butterflies have a four-stage life cycle, as like most insects they undergocomplete metamorphosis. Winged adults lay eggs on the food plant on which theirlarvae, known ascaterpillars, will feed. The caterpillars grow, sometimes very rapidly, and when fully developed,pupatein achrysalis. Whenmetamorphosisis complete, the pupal skin splits, the adult insect climbs out, and after its wings have expanded and dried, it flies off. Some butterflies, especially in the tropics, have several generations in a year, while others have a single generation, and a few in cold locations may take several years to pass through their entire life cycle. Butterflies are oftenpolymorphic, and many species make use ofcamouflage,mimicry, andaposematismto evade their predators.[1]Some, like themonarchand thepainted lady,migrateover long distances. Many butterflies are attacked byparasitesorparasitoids, includingwasps,protozoans,flies, and other invertebrates, or arepreyed uponby other organisms. Some species are pests because in their larval stages they can damage domestic crops or trees; other species are agents ofpollinationof some plants. Larvae of a few butterflies (e.g.,harvesters) eat harmful insects, and a few are predators ofants, while others live asmutualistsin association with ants. Culturally, butterflies are a popular motif in the visual and literary arts. TheSmithsonian Institutionsays "butterflies are certainly one of the most appealing creatures in nature".[2] Contents Etymology  Possibly the original butter-fly.[3]A male brimstone (Gonepteryx rhamni) in flight TheOxford English Dictionaryderives the word straightforwardly fromOld Englishbutorflēoge, butter-fly; similar names inOld DutchandOld High Germanshow that the name is ancient, but modern Dutch and German use different words (vlinderandSchmetterling) and the common name often varies substantially between otherwise closely-related languages. A possible source of the name is the bright yellow male of the brimstone (Gonepteryx rhamni); another is that butterflies were on the wing in meadows during the spring and summer butter season while the grass was growing.[3][4] Paleontology Further information:Prehistoric Lepidoptera The earliestLepidopterafossils date to theTriassic-Jurassicboundary, around 200 million years ago.[5]Butterflies evolved from moths, so while the butterflies aremonophyletic(forming a singleclade), the moths are not. The oldest known butterfly isProtocoeliades kristensenifrom thePalaeoceneagedFur Formationof Denmark, approximately 55 million years old, which belongs to the familyHesperiidae(skippers).[6]Molecular clockestimates suggest that butterflies originated sometime in the mid-Cretaceous, but only significantly diversified during the Cenozoic.[7]The oldest American butterfly is theLate EoceneProdryas persephonefrom theFlorissant Fossil Beds,[8][9]approximately 34 million years old.[10] Butterfly Fossils  Prodryas persephone, aLate Eocenebutterfly from theFlorissant Fossil Beds, 1887 engraving  Lithopsyche antiqua, anEarly Oligocenebutterfly from the Bembridge Marls,Isle of Wight, 1889 engraving Taxonomy and phylogeny Further information:Taxonomy of the Lepidoptera Traditionally, butterflies have been divided into thesuperfamilyPapilionoideaexcluding the smaller groups of theHesperiidae(skippers) and the more moth-likeHedylidaeof America.Phylogeneticanalysis suggests that the traditional Papilionoidea isparaphyleticwith respect to the other two groups, so they should both be included within Papilionoidea, to form a single butterfly group, thereby synonymous with the cladeRhopalocera.[11][12] Butterfly familiesFamilyCommon nameCharacteristicsImageHedylidaeAmerican moth-butterfliesSmall, brown, likegeometrid moths;antennaenot clubbed; long slim abdomenHesperiidaeSkippersSmall, darting flight; clubs on antennae hooked backwardsLycaenidaeBlues, coppers, hairstreaksSmall, brightly coloured; often have false heads with eyespots and small tails resembling antennaeNymphalidaeBrush-footed or four-footed butterfliesUsually have reduced forelegs, so appear four-legged; often brightly colouredPapilionidaeSwallowtailsOften have 'tails' on wings; caterpillar generates foul taste withosmeteriumorgan; pupa supported by silk girdlePieridaeWhites and alliesMostly white, yellow or orange; some serious pests ofBrassica; pupa supported by silk girdleRiodinidaeMetalmarksOften have metallic spots on wings; often conspicuously coloured with black, orange and blue Biology  The wings of butterflies, hereAglais io, are covered with coloured scales. General description  Butterfly antennal shapes, mainly clubbed, unlike those of moths. Drawn by C. T. Bingham, 1905 Further information:Glossary of entomology termsandComparison of butterflies and moths  Unlike butterflies, most moths (likeLaothoe populi) fly by night and hide by day. Butterfly adults are characterized by their four scale-covered wings, which give the Lepidoptera their name (Ancient Greekλεπίς lepís, scale + πτερόν pterón, wing). These scales give butterfly wings their colour: they are pigmented withmelaninsthat give them blacks and browns, as well asuric acidderivatives andflavonesthat give them yellows, but many of the blues, greens, reds andiridescent coloursare created bystructural colorationproduced by the micro-structures of the scales and hairs.[13][14][15][16] As in all insects, the body is divided into three sections: the head,thorax, andabdomen. The thorax is composed of three segments, each with a pair of legs. In most families of butterfly the antennae are clubbed, unlike those ofmothswhich may be threadlike or feathery. The long proboscis can be coiled when not in use for sipping nectar from flowers.[17] Nearly all butterflies arediurnal, have relatively bright colours, and hold their wings vertically above their bodies when at rest, unlike the majority of moths which fly by night, are oftencrypticallycoloured (well camouflaged), and either hold their wings flat (touching the surface on which the moth is standing) or fold them closely over their bodies. Some day-flying moths, such as thehummingbird hawk-moth,[18]are exceptions to these rules.[17][19] Sexual dimorphisminAnthocharis cardamines Male Female Butterflylarvae,caterpillars, have a hard (sclerotised) head with strong mandibles used for cutting their food, most often leaves. They have cylindrical bodies, with ten segments to the abdomen, generally with short prolegs on segments 3–6 and 10; the three pairs of true legs on the thorax have five segments each.[17]Many are well camouflaged; others are aposematic with bright colours and bristly projections containing toxic chemicals obtained from their food plants. Thepupaor chrysalis, unlike that of moths, is not wrapped in a cocoon.[17] Many butterflies aresexually dimorphic. Most butterflies have theZW sex-determination systemwhere females are the heterogametic sex (ZW) and males homogametic (ZZ).[20] Distribution and migration See also: Lists of butterflies ofAustralia(Tasmania,Victoria),Britain,India,Menorca,North America,Taiwan, andTrinidad and Tobago Further information:Lepidoptera migration,Insect migration, andAnimal navigation Butterflies are distributed worldwide except Antarctica, totalling some 18,500 species.[21]Of these, 775 areNearctic; 7,700Neotropical; 1,575Palearctic; 3,650Afrotropical; and 4,800 are distributed across the combinedOrientalandAustralian/Oceaniaregions.[21]Themonarch butterflyis native to the Americas, but in the nineteenth century or before, spread across the world, and is now found in Australia, New Zealand, other parts of Oceania, and theIberian Peninsula. It is not clear how it dispersed; adults may have been blown by the wind or larvae or pupae may have been accidentally transported by humans, but the presence of suitable host plants in their new environment was a necessity for their successful establishment.[22]  Monarchmigration route  Overwintering monarchs cluster onoyameltrees nearAngangueo, Mexico. Many butterflies, such as thepainted lady, monarch, and severaldanainemigrate for long distances. These migrations take place over a number of generations and no single individual completes the whole trip. The eastern North American population of monarchs can travel thousands of miles south-west tooverwintering sites in Mexico. There is a reverse migration in the spring.[23][24]It has recently been shown that the British painted lady undertakes a 9,000-mile round trip in a series of steps by up to six successive generations, from tropical Africa to the Arctic Circle — almost double the length of the famous migrations undertaken by monarch.[25]Spectacular large-scale migrations associated with themonsoonare seen in peninsular India.[26]Migrations have been studied in more recent times using wing tags and also usingstable hydrogen isotopes.[27][28] Butterflies navigate using a time-compensated sun compass. They can see polarized light and therefore orient even in cloudy conditions. The polarized light near the ultraviolet spectrum appears to be particularly important.[29][30]Many migratory butterflies live in semi-arid areas where breeding seasons are short.[31]The life histories of their host plants also influence butterfly behaviour.[32] Life cycle  Life cycle of the monarch butterfly  Mating pair ofspotted fritillariesongreater pignut Butterflies in their adult stage can live from a week to nearly a year depending on the species. Many species have long larval life stages while others can remaindormantin their pupal or egg stages and thereby survive winters.[33]TheMelissa Arctic(Oeneis melissa) overwinters twice as a caterpillar.[34]Butterflies may have one or more broods per year. The number of generations per year varies fromtemperatetotropical regionswith tropical regions showing a trend towardsmultivoltinism.[35]  The male small skipper (Thymelicus sylvestris) haspheromone-releasing "sex brands" (dark line) on the upperside of its forewings. Courtshipis often aerial and often involvespheromones. Butterflies then land on the ground or on a perch to mate.[17]Copulation takes place tail-to-tail and may last from minutes to hours. Simple photoreceptor cells located at the genitals are important for this and other adult behaviours.[36]The male passes aspermatophoreto the female; to reduce sperm competition, he may cover her with his scent, or in some species such as the Apollos (Parnassius)plugs her genital openingto prevent her from mating again.[37] The vast majority of butterflies have a four-stage life cycle;egg,larva(caterpillar),pupa(chrysalis) andimago(adult). In the generaColias,Erebia,Euchloe, andParnassius, a small number of species are known that reproducesemi-parthenogenetically; when the female dies, a partially developed larva emerges from her abdomen.[38] Egg  Eggs of black-veined white (Aporia crataegi) onappleleaf  A butterfly laying eggs underneath the leaf Butterfly eggs are protected by a hard-ridged outer layer of shell, called thechorion. This is lined with a thin coating of wax which prevents the egg from drying out before the larva has had time to fully develop. Each egg contains a number of tiny funnel-shaped openings at one end, calledmicropyles; the purpose of these holes is to allow sperm to enter and fertilize the egg. Butterfly eggs vary greatly in size and shape between species, but are usually upright and finely sculptured. Some species lay eggs singly, others in batches. Many females produce between one hundred and two hundred eggs.[38] Butterfly eggs are fixed to a leaf with a special glue which hardens rapidly. As it hardens it contracts, deforming the shape of the egg. This glue is easily seen surrounding the base of every egg forming a meniscus. The nature of the glue has been little researched but in the case ofPieris brassicae, it begins as a pale yellow granular secretion containing acidophilic proteins. This is viscous and darkens when exposed to air, becoming a water-insoluble, rubbery material which soon sets solid.[39]Butterflies in the genusAgathymusdo not fix their eggs to a leaf, instead the newly laid eggs fall to the base of the plant.[40] Eggs are almost invariably laid on plants. Each species of butterfly has its own host plant range and while some species of butterfly are restricted to just one species of plant, others use a range of plant species, often including members of a common family.[41]In some species, such as thegreat spangled fritillary, the eggs are deposited close to but not on the food plant. This most likely happens when the egg overwinters before hatching and where the host plant loses its leaves in winter, as dovioletsin this example.[42] The egg stage lasts a few weeks in most butterflies, but eggs laid close to winter, especially in temperate regions, go through adiapause(resting) stage, and the hatching may take place only in spring.[43]Some temperate region butterflies, such as theCamberwell beauty, lay their eggs in the spring and have them hatch in the summer.[44] Caterpillar larva  Aposematiccaterpillar ofPapilio machaon, in threat pose Butterfly larvae, or caterpillars, consume plant leaves and spend practically all of their time searching for and eating food. Although most caterpillars are herbivorous, a few species arepredators:Spalgis epiuseatsscale insects,[45]while lycaenids such asLiphyra brassolisaremyrmecophilous, eating ant larvae.[46]  Mutualism: ant tending alycaenidcaterpillar,Catapaecilma major Some larvae, especially those of theLycaenidae, formmutual associationswith ants. They communicate with the ants using vibrations that are transmitted through thesubstrateas well as using chemical signals.[47][48]The ants provide some degree of protection to these larvae and they in turn gatherhoneydew secretions.Large blue(Phengaris arion) caterpillars trickMyrmicaants into taking them back to theant colonywhere they feed on the ant eggs and larvae in a parasitic relationship.[49]  Crypticcountershadedcaterpillar of a hawkmoth,Ceratomia amyntor Caterpillars mature through a series of developmental stages known asinstars. Near the end of each stage, the larva undergoes a process calledapolysis, mediated by the release of a series ofneurohormones. During this phase, thecuticle, a tough outer layer made of a mixture ofchitinand specializedproteins, is released from the softerepidermisbeneath, and the epidermis begins to form a new cuticle. At the end of each instar, the larvamoults, the old cuticle splits and the new cuticle expands, rapidly hardening and developing pigment.[50]Development of butterfly wing patterns begins by the last larval instar. Caterpillars have short antennae and severalsimple eyes. Themouthpartsare adapted for chewing with powerful mandibles and a pair of maxillae, each with a segmented palp. Adjoining these is the labium-hypopharynx which houses a tubular spinneret which is able to extrude silk.[13]Caterpillars such as those in the genusCalpodes(family Hesperiidae) have a specialized tracheal system on the 8th segment that function as a primitive lung.[51]Butterfly caterpillars have three pairs of true legs on the thoracic segments and up to six pairs ofprolegsarising from the abdominal segments. These prolegs have rings of tiny hooks called crochets that are engaged hydrostatically and help the caterpillar grip the substrate.[52]The epidermis bears tufts ofsetae, the position and number of which help in identifying the species. There is also decoration in the form of hairs, wart-like protuberances, horn-like protuberances and spines. Internally, most of the body cavity is taken up by the gut, but there may also be large silk glands, and special glands which secrete distasteful or toxic substances. The developing wings are present in later stage instars and thegonadsstart development in the egg stage.[13] Pupa  Chrysalisofgulf fritillary When the larva is fully grown, hormones such asprothoracicotropic hormone(PTTH) are produced. At this point the larva stops feeding, and begins "wandering" in the quest for a suitable pupation site, often the underside of a leaf or other concealed location. There it spins a button of silk which it uses to fasten its body to the surface and moults for a final time. While some caterpillars spin acocoonto protect the pupa, most species do not. The naked pupa, often known as a chrysalis, usually hangs head down from the cremaster, a spiny pad at the posterior end, but in some species a silken girdle may be spun to keep the pupa in a head-up position.[38]Most of the tissues and cells of the larva are broken down inside the pupa, as the constituent material is rebuilt into the imago. The structure of the transforming insect is visible from the exterior, with the wings folded flat on the ventral surface and the two halves of the proboscis, with the antennae and the legs between them.[13] The pupal transformation into a butterfly throughmetamorphosishas held great appeal to mankind. To transform from the miniature wings visible on the outside of the pupa into large structures usable for flight, the pupal wings undergo rapid mitosis and absorb a great deal of nutrients. If one wing is surgically removed early on, the other three will grow to a larger size. In the pupa, the wing forms a structure that becomes compressed from top to bottom and pleated from proximal to distal ends as it grows, so that it can rapidly be unfolded to its full adult size. Several boundaries seen in the adult colour pattern are marked by changes in the expression of particular transcription factors in the early pupa.[53] Adult  An adultParthenos sylviabutterfly The reproductive stage of the insect is the winged adult orimago. The surface of both butterflies and moths is covered by scales, each of which is an outgrowth from a singleepidermalcell. The head is small and dominated by the two largecompound eyes. These are capable of distinguishing flower shapes or motion but cannot view distant objects clearly. Colour perception is good, especially in some species in the blue/violet range. Theantennaeare composed of many segments and have clubbed tips (unlike moths that have tapering or feathery antennae). The sensory receptors are concentrated in the tips and can detect odours. Taste receptors are located on the palps and on the feet. The mouthparts are adapted to sucking and themandiblesare usually reduced in size or absent. The first maxillae are elongated into a tubularprobosciswhich is curled up at rest and expanded when needed to feed. The first and second maxillae bear palps which function as sensory organs. Some species have a reduced proboscis or maxillary palps and do not feed as adults.[13] ManyHeliconiusbutterflies also use their proboscis to feed on pollen;[54]in these species only 20% of the amino acids used in reproduction come from larval feeding, which allow them to develop more quickly as caterpillars, and gives them a longer lifespan of several months as adults.[55] The thorax of the butterfly is devoted to locomotion. Each of the three thoracic segments has two legs (amongnymphalids, the first pair is reduced and the insects walk on four legs). The second and third segments of the thorax bear the wings. The leading edges of the forewings have thick veins to strengthen them, and the hindwings are smaller and more rounded and have fewer stiffening veins. The forewings and hindwings are not hooked together (as they are in moths) but are coordinated by the friction of their overlapping parts. The front two segments have a pair ofspiracleswhich are used in respiration.[13] The abdomen consists of ten segments and contains the gut and genital organs. The front eight segments have spiracles and the terminal segment is modified for reproduction. The male has a pair of clasping organs attached to a ring structure, and during copulation, a tubular structure is extruded and inserted into the female's vagina. Aspermatophoreis deposited in the female, following which the sperm make their way to a seminal receptacle where they are stored for later use. In both sexes, the genitalia are adorned with various spines, teeth, scales and bristles, which act to prevent the butterfly from mating with an insect of another species.[13]After it emerges from its pupal stage, a butterfly cannot fly until the wings are unfolded. A newly emerged butterfly needs to spend some time inflating its wings withhemolymphand letting them dry, during which time it is extremely vulnerable to predators.[56] Pattern formation The colorful patterns on many butterfly wings tell potential predators that they are toxic. Hence, the genetic basis of wingpattern formationcan illuminate both theevolutionof butterflies as well as theirdevelopmental biology. The color of butterfly wings is derived from tiny structures called scales, each of which have their ownpigments. InHeliconiusbutterflies, there are three types of scales: yellow/white, black, and red/orange/brown scales. Some mechanism of wing pattern formation are now being solved using genetic techniques. For instance, agenecalledcortexdetermines the color of scales: deletingcortexturned black and red scales yellow. Mutations, e.g.transposon insertionsof the non-coding DNA around thecortexgene can turn a black-winged butterfly into a butterfly with a yellow wing band.[57] Behaviour  AnAustralian painted ladyfeeding on a flowering shrub Butterflies feed primarily onnectarfrom flowers. Some also derive nourishment frompollen,[58]tree sap, rotting fruit, dung, decaying flesh, and dissolved minerals in wet sand or dirt. Butterflies are important as pollinators for some species of plants. In general, they do not carry as much pollen load asbees, but they are capable of moving pollen over greater distances.[59]Flower constancyhas been observed for at least one species of butterfly.[60] Adult butterflies consume only liquids, ingested through the proboscis. They sip water from damp patches for hydration and feed on nectar from flowers, from which they obtain sugars for energy, andsodiumand other minerals vital for reproduction. Several species of butterflies need more sodium than that provided by nectar and are attracted by sodium in salt; they sometimes land on people, attracted by the salt in human sweat. Some butterflies also visit dung and scavenge rotting fruit or carcasses to obtain minerals and nutrients. In many species, thismud-puddlingbehaviour is restricted to the males, and studies have suggested that the nutrients collected may be provided as anuptial gift, along with the spermatophore, during mating.[61] Inhilltopping, males of some species seek hilltops and ridge tops, which they patrol in search for females. Since it usually occurs in species with low population density, it is assumed these landscape points are used as meeting places to find mates.[62] Butterflies use their antennae to sense the air for wind and scents. The antennae come in various shapes and colours; the hesperiids have a pointed angle or hook to the antennae, while most other families show knobbed antennae. The antennae are richly covered with sensory organs known assensillae. A butterfly's sense of taste is coordinated by chemoreceptors on thetarsi, or feet, which work only on contact, and are used to determine whether an egg-laying insect's offspring will be able to feed on a leaf before eggs are laid on it.[63]Many butterflies use chemical signals,pheromones; some have specialized scent scales (androconia) or other structures (coremataor "hair pencils" in the Danaidae).[64]Vision is well developed in butterflies and most species are sensitive to the ultraviolet spectrum. Many species show sexual dimorphism in the patterns of UV reflective patches.[65]Colour vision may be widespread but has been demonstrated in only a few species.[66][67]Some butterflies have organs of hearing and some species makestridulatoryand clicking sounds.[68]  Heteronympha meropetaking off Many species of butterfly maintain territories and actively chase other species or individuals that may stray into them. Some species will bask or perch on chosen perches. The flight styles of butterflies are often characteristic and some species have courtship flight displays. Butterflies can only fly when their temperature is above 27°C (81°F); when it is cool, they can position themselves to expose the underside of the wings to the sunlight to heat themselves up. If their body temperature reaches 40°C (104°F), they can orientate themselves with the folded wings edgewise to the sun.[69]Basking is an activity which is more common in the cooler hours of the morning. Some species have evolved dark wingbases to help in gathering more heat and this is especially evident in alpine forms.[70] As in many other insects, theliftgenerated by butterflies is more than can be accounted for by steady-state, non-transitoryaerodynamics. Studies usingVanessa atalantain awind tunnelshow that they use a wide variety of aerodynamic mechanisms to generate force. These includewake capture,vorticesat the wing edge, rotational mechanisms and theWeis-Fogh'clap-and-fling' mechanism. Butterflies are able to change from one mode to another rapidly.[71] Ecology  Braconidparasitoidalwasp (Apantelesspecies) cocoons attached to lime butterfly (Papilio demoleus) caterpillar Parasitoids, predators, and pathogens Butterflies are threatened in their early stages byparasitoidsand in all stages by predators, diseases and environmental factors.Braconidand other parasitic wasps lay their eggs in lepidopteran eggs or larvae and the wasps' parasitoid larvae devour their hosts, usually pupating inside or outside the desiccated husk. Most wasps are very specific about their host species and some have been used as biological controls of pest butterflies like thelarge white butterfly.[72]When thesmall cabbage whitewas accidentally introduced to New Zealand, it had no natural enemies. In order to control it, some pupae that had been parasitised by a chalcid wasp were imported, and natural control was thus regained.[73]Some flies lay their eggs on the outside of caterpillars and the newly hatched fly larvae bore their way through the skin and feed in a similar way to the parasitoid wasp larvae.[74]Predators of butterflies include ants, spiders, wasps, and birds.[75] Caterpillars are also affected by a range of bacterial, viral and fungal diseases, and only a small percentage of the butterfly eggs laid ever reach adulthood.[74]The bacteriumBacillus thuringiensishas been used in sprays to reduce damage to crops by the caterpillars of the large white butterfly, and theentomopathogenic fungusBeauveria bassianahas proved effective for the same purpose.[76] Endangered species Queen Alexandra's birdwingis the largest butterfly in the world. The species isendangered, and is one of only three insects (the other two being butterflies as well) to be listed onAppendix IofCITES, making international trade illegal.[77] Black grass-dart butterfly(Ocybadistes knightorum)is a butterfly of the familyHesperiidae. It is endemic toNew South Wales. It has a very limited distribution in theBoambeearea. Defences  Heliconiuswarns off predators withMüllerian mimicry.[78] Further information:Defense in insects,Anti-predator adaptation,Mimicry, andSeasonal polyphenism Butterflies protect themselves from predators by a variety of means.  Giant swallowtailcaterpillar everting itsosmeteriumin defence; it is alsomimetic, resembling a bird dropping. Chemical defences are widespread and are mostly based on chemicals of plant origin. In many cases the plants themselves evolved these toxic substances asprotectionagainst herbivores. Butterflies have evolved mechanisms to sequester these plant toxins and use them instead in their own defence.[79]These defence mechanisms are effective only if they are well advertised; this has led to the evolution of bright colours in unpalatable butterflies (aposematism). This signal is commonlymimickedby other butterflies, usually only females. ABatesian mimicimitates another species to enjoy the protection of that species' aposematism.[80]Thecommon Mormonof India has female morphs which imitate the unpalatable red-bodied swallowtails, thecommon roseand thecrimson rose.[81]Müllerian mimicryoccurs when aposematic species evolve to resemble each other, presumably to reduce predator sampling rates;Heliconiusbutterflies from the Americas are a good example.[80]  Eyespots ofspeckled wood(Pararge aegeria) distract predators from attacking the head. This insect can still fly with a damaged left hindwing. Camouflageis found in many butterflies. Some like the oakleaf butterfly andautumn leafare remarkable imitations of leaves.[82]As caterpillars, many defend themselves by freezing and appearing like sticks or branches.[83]Others havedeimaticbehaviours, such as rearing up and waving their front ends which are marked with eyespots as if they were snakes.[84]Some papilionid caterpillars such as the giant swallowtail (Papilio cresphontes) resemble bird droppings so as to be passed over by predators.[85]Some caterpillars have hairs and bristly structures that provide protection while others are gregarious and form dense aggregations.[80]Some species aremyrmecophiles, formingmutualistic associationswithantsand gaining their protection.[86]Behavioural defences include perching and angling the wings to reduce shadow and avoid being conspicuous. Some femaleNymphalidbutterflies guard their eggs from parasitoidalwasps.[87] The Lycaenidae have a false head consisting of eyespots and small tails (false antennae) to deflect attack from the more vital head region. These may also cause ambush predators such as spiders to approach from the wrong end, enabling the butterflies to detect attacks promptly.[88][89]Many butterflies haveeyespotson the wings; these too may deflect attacks, or may serve to attract mates.[53][90] Auditory defences can also be used, which in the case of thegrizzled skipperrefers to vibrations generated by the butterfly upon expanding its wings in an attempt to communicate with ant predators.[91] Many tropical butterflies haveseasonal formsfor dry and wet seasons.[92][93]These are switched by the hormoneecdysone.[94]The dry-season forms are usually more cryptic, perhaps offering better camouflage when vegetation is scarce. Dark colours in wet-season forms may help to absorb solar radiation.[95][96][90] Butterflies without defences such as toxins or mimicry protect themselves through a flight that is more bumpy and unpredictable than in other species. It is assumed this behavior makes it more difficult for predators to catch them, and is caused by theturbulencecreated by the small whirlpools formed by the wings during flight.[97] Declining numbers Declining butterfly populations have been noticed in many areas of the world, and this phenomenon is consistent with therapidly decreasing insect populations around the world. At least in the Western United States, this collapse in the number of most species of butterflies has been determined to be driven byglobal climate change, specifically, by warmer autumns.[98][99] In culture  Ancient Egyptianrelief sculpture,26th dynasty,Thebes. c. 664–525 BC In art and literature  Butterfly and Chinesewisteria, by Xü Xi. EarlySong Dynasty, c. 970  A butterfly in the coat of arms ofPerho Butterflies have appeared in art from 3500 years ago inancient Egypt.[100]In the ancientMesoamericancity ofTeotihuacan, the brilliantly coloured image of the butterfly was carved into many temples, buildings, jewellery, and emblazoned onincense burners. The butterfly was sometimes depicted with the maw of ajaguar, and some species were considered to be the reincarnations of the souls of dead warriors. The close association of butterflies with fire and warfare persisted into theAztec civilisation; evidence of similar jaguar-butterfly images has been found among theZapotecandMaya civilisations.[101] Butterflies are widely used in objects of art and jewellery: mounted in frames, embedded in resin, displayed in bottles, laminated in paper, and used in some mixed media artworks and furnishings.[102]TheNorwegiannaturalistKjell Sandvedcompiled a photographicButterfly Alphabetcontaining all 26 letters and the numerals 0 to 9 from the wings of butterflies.[103]  Alicemeets thecaterpillar. Illustration by SirJohn TennielinLewis Carroll'sAlice in Wonderland, c. 1865 SirJohn Tennieldrew a famous illustration ofAlicemeeting acaterpillarforLewis Carroll'sAlice in Wonderland, c. 1865. The caterpillar is seated on a toadstool and is smoking ahookah; the image can be read as showing either the forelegs of the larva, or as suggesting a face with protruding nose and chin.[3]Eric Carle's children's bookThe Very Hungry Caterpillarportrays the larva as an extraordinarily hungry animal, while also teaching children how to count (to five) and the days of the week.[3] A butterfly appeared in one ofRudyard Kipling'sJust So Stories, "The Butterfly that Stamped".[104] One of the most popular, and most often recorded, songs bySweden's eighteenth-century bard,Carl Michael Bellman, is "Fjäriln vingad syns på Haga" (The butterfly wingèd is seen in Haga), one of hisFredman's Songs.[105] Madam Butterflyis a 1904operabyGiacomo Pucciniabout a romantic young Japanese bride who is deserted by her American officer husband soon after they are married. It was based onJohn Luther Long's short story written in 1898.[106] In mythology and folklore  Der Schmetterlingsjäger(The butterfly hunter) painting byCarl Spitzweg, 1840 According toLafcadio Hearn, a butterfly was seen in Japan as the personification of a person's soul; whether they be living, dying, or already dead. One Japanese superstition says that if a butterfly enters your guest room and perches behind the bamboo screen, the person whom you most love is coming to see you. Large numbers of butterflies are viewed as badomens. WhenTaira no Masakadowas secretly preparing for his famous revolt, there appeared inKyotoso vast a swarm of butterflies that the people were frightened—thinking the apparition to be a portent of coming evil.[107]  A serving tray decorated with butterfly wings Diderot'sEncyclopédiecites butterflies as a symbol for the soul. A Roman sculpture depicts a butterfly exiting the mouth of a dead man, representing the Roman belief that the soul leaves through the mouth.[108]In line with this, the ancient Greek word for "butterfly" is ψυχή (psȳchē), which primarily means "soul" or "mind".[109]According toMircea Eliade, some of theNagasofManipurclaim ancestry from a butterfly.[110]In some cultures, butterflies symboliserebirth.[111]The butterfly is a symbol of beingtransgender, because of the transformation from caterpillar to winged adult.[112]In the English county ofDevon, people once hurried to kill the first butterfly of the year, to avoid a year of bad luck.[113]In the Philippines, a lingering black or dark butterfly or moth in the house is taken to mean an impending or recent death in the family.[114]Several American states have chosen anofficial state butterfly.[115] Collecting, recording, and rearing  Nōrobe Japan 1700s. Silk embroidered with silk thread and stenciled with gold foil "Collecting" means preserving dead specimens, not keeping butterflies as pets.[116][117]Collecting butterflies was once a popular hobby; it has now largely been replaced by photography, recording, and rearing butterflies for release into the wild.[3][dubious–discuss][full citation needed]The zoological illustratorFrederick William Frohawksucceeded in rearing all the butterfly species found in Britain, at a rate of four per year, to enable him to draw every stage of each species. He published the results in the folio sized handbookThe Natural History of British Butterfliesin 1924.[3] Butterflies andmothscan be reared for recreation or for release.[118] In technology Further information:Biomimetics Study of thestructural colorationof the wing scales of swallowtail butterflies has led to the development of more efficientlight-emitting diodes,[119]and is inspiringnanotechnologyresearch to produce paints that do not use toxic pigments and the development of new display technologies.[120]

Fishareaquatic,craniate,gill-bearing animals that lacklimbswithdigits. Included in this definition are the livinghagfish,lampreys, andcartilaginousandbony fishas well as various extinct related groups. Approximately 95% of living fish species are ray-finned fish, belonging to the classActinopterygii, with around 99% of those beingteleosts. Fish Temporal range:535–0Ma PreꞒ Ꞓ O S D C P T J K Pg N Middle Cambrian-Recent Giant grouperswimming amongschoolsof other fishHead-on view of ared lionfishScientific classificationKingdom:AnimaliaPhylum:ChordataClade:OlfactoresSubphylum:VertebrataGroups includedJawless fish†Armoured fish†Spiny sharksCartilaginous fishBony fishRay-finned fishLobe-finned fishCladisticallyincluded but traditionally excluded taxaTetrapods†Conodonts The earliest organisms that can be classified as fish were soft-bodiedchordatesthat first appeared during theCambrianperiod. Although they lacked atrue spine, they possessednotochordswhich allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through thePaleozoicera, diversifying into a wide variety of forms. Many fish of the Paleozoic developedexternal armorthat protected them from predators. The first fish withjawsappeared in theSilurianperiod, after which many (such assharks) became formidable marine predators rather than just the prey ofarthropods. Most fish areectothermic("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers likewhite sharkandtunacan hold a highercore temperature.[1][2]Fish can acoustically communicate with each other, most often in the context of feeding, aggression or courtship.[3] Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g.,charandgudgeon) to theabyssaland evenhadaldepths of the deepest oceans (e.g.,cusk-eelsandsnailfish), although no species has yet been documented in the deepest 25% of the ocean.[4]With 34,300 described species, fish exhibit greater species diversity than any other group of vertebrates.[5] Fish are an important resource for humans worldwide, especiallyas food. Commercial and subsistence fishers hunt fish inwild fisheriesorfarmthem in ponds or in cages in the ocean (inaquaculture). They are also caught byrecreational fishers, kept as pets, raised byfishkeepers, and exhibited in publicaquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies. Tetrapods(amphibians,reptiles,birdsandmammals) emerged withinlobe-finned fishes, socladisticallythey are fish as well. However, traditionally fish (piscesorichthyes) are renderedparaphyleticby excluding the tetrapods, and are therefore not considered a formal taxonomic grouping insystematic biology, unless it is used in thecladisticsense, including tetrapods,[6][7]although usually "vertebrate" is preferred and used for this purpose (fish plus tetrapods) instead. Furthermore,cetaceans, although mammals, have often been considered fish by various cultures and timeperiods. Contents Etymology The word forfishin English and the otherGermanic languages(GermanFisch;Gothicfisks) is inherited fromProto-Germanic, and is related to theLatinpiscisandOld Irishīasc, though the exact root is unknown; some authorities reconstruct anProto-Indo-Europeanroot*peysk-, attested only inItalic,Celtic, andGermanic.[8][9][10][11] The English word once had a much broader usage than its current biological meaning. Names such asstarfish,jellyfish,shellfishandcuttlefishattest to almost any fully aquatic animal (including whales) once beingfish. "Correcting" such names (e.g. tosea star) is an attempt to retroactively apply the current meaning offishto words that were coined when it had a different meaning. Evolution Main article:Evolution of fish Fish, as vertebrata, developed as sister of the tunicata. As the tetrapods emerged deep within the fishes group, as sister of the lungfish, characteristics of fish are typically shared by tetrapods, including having vertebrae and a cranium.  Dunkleosteuswas a gigantic, 10-metre (33ft) longprehistoric fishof class Placodermi.  Lower jaw of the placodermEastmanosteuspustulosus, showing the shearing structures ("teeth") on its oral surface; from theDevonianofWisconsin Early fish from the fossil record are represented by a group of small, jawless, armored fish known asostracoderms. Jawless fish lineages are mostly extinct. An extant clade, thelampreysmay approximate ancient pre-jawed fish. The first jaws are found inPlacodermifossils. They lacked distinct teeth, having instead the oral surfaces of their jaw plates modified to serve the various purposes of teeth. The diversity of jawed vertebrates may indicate the evolutionary advantage of ajawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors. Fish may have evolved from a creature similar to a coral-likesea squirt, whose larvae resemble primitive fish in important ways. The first ancestors of fish may havekept the larval form into adulthood(as some sea squirts do today). Phylogeny Fishes are aparaphyleticgroup: that is, anycladecontaining all fish also contains thetetrapods, which are not fish (though they include fish-shaped forms, such asWhales and Dolphinsor theextinctichthyosaurs, which acquired a fish-like body shape due tosecondary aquatic adaptation, seeevolution of cetaceans). The followingcladogramshowsclades- some with, some withoutextantrelatives - that are traditionally considered as "fishes" (cyanline) and the tetrapods (four-limbed vertebrates), which are mostly terrestrial.Extinctgroups are marked with adagger(†). Vertebrata/ Agnatha/  Hyperoartia(lampreys)    Myxini(hagfish)  Cyclostomes   †Euconodonta     †Pteraspidomorphi    †Thelodonti     †Anaspida     †Galeaspida     †Pituriaspida    †Osteostraci  Gnathostomata  "†Placodermi" (armoured fishes,paraphyletic)[13]     "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)[14]   Chondrichthyes  "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)     Holocephali(ratfish)    Euselachii(sharks,rays)   (cartilaginousfishes)Euteleostomi/  "†Acanthodii" ("spiny sharks",paraphyleticorpolyphyletic)    Actinopterygii  Cladistia(bichirs,reedfish)     Chondrostei(sturgeons,paddlefish)    Neopterygii(includesTeleostei, 96% of living fishspecies)   (ray‑finnedfishes)Sarcopterygii  †Onychodontiformes    Actinistia(coelacanths)  Rhipidistia   †Porolepiformes    Dipnoi(lungfishes)   Tetrapodomorpha/   †Rhizodontimorpha     †Tristichopteridae     †Tiktaalik  Tetrapoda  †Ichthyostega    crown-grouptetrapods  four‑limbedvertebrates   (Choanata) (lobe‑finnedfish)  Osteichthyes  (jawedvertebrates)     "Fishes" Craniata Taxonomy  Leedsichthys,of the subclass Actinopterygii, is the largest known fish, with estimates in 2005 putting its maximum size at 16 metres (52ft). Fishes are aparaphyleticgroup and for this reason, groups such as the classPiscesseen in older reference works are no longer used in formal classifications. Traditional classification divides fish into threeextantclasses, and with extinct forms sometimes classified within the tree, sometimes as their own classes:[15][16] ClassAgnatha(jawless fish) SubclassCyclostomata(hagfishandlampreys) SubclassOstracodermi(armoured jawless fish) † ClassChondrichthyes(cartilaginous fish) SubclassElasmobranchii(sharksandrays) SubclassHolocephali(chimaerasand extinct relatives) ClassPlacodermi(armoured fish) † ClassAcanthodii("spiny sharks", sometimes classified under bony fishes)† ClassOsteichthyes(bony fish) SubclassActinopterygii(ray finned fishes) SubclassSarcopterygii(fleshy finned fishes, ancestors of tetrapods) The above scheme is the one most commonly encountered in non-specialist and general works. Many of the above groups are paraphyletic, in that they have given rise to successive groups: Agnathans are ancestral to Chondrichthyes, who again have given rise to Acanthodiians, the ancestors of Osteichthyes. With the arrival ofphylogenetic nomenclature, the fishes has been split up into a more detailed scheme, with the following major groups: Class Myxini (hagfish) ClassPteraspidomorphi† (early jawless fish) ClassThelodonti† ClassAnaspida† ClassPetromyzontida or Hyperoartia Petromyzontidae (lampreys) ClassConodonta(conodonts) † ClassCephalaspidomorphi† (early jawless fish) (unranked)Galeaspida† (unranked)Pituriaspida† (unranked)Osteostraci† InfraphylumGnathostomata(jawed vertebrates) ClassPlacodermi† (armoured fish) ClassChondrichthyes(cartilaginous fish) ClassAcanthodii† (spiny sharks) SuperclassOsteichthyes(bony fish) ClassActinopterygii(ray-finned fish) SubclassChondrostei OrderAcipenseriformes(sturgeonsandpaddlefishes) OrderPolypteriformes(reedfishesandbichirs). SubclassNeopterygii InfraclassHolostei(garsandbowfins) InfraclassTeleostei(many orders of common fish) ClassSarcopterygii(lobe-finned fish) SubclassActinistia(coelacanths) Subclass Dipnoi (lungfish, sister group to thetetrapods) † – indicates extinct taxon Some palaeontologists contend that becauseConodontaarechordates, they are primitive fish. For a fuller treatment of this taxonomy, see thevertebratearticle. The position ofhagfishin the phylum Chordata is not settled. Phylogenetic research in 1998 and 1999 supported the idea that the hagfish and the lampreys form a natural group, theCyclostomata, that is a sister group of the Gnathostomata.[17][18] The various fish groups account for more than half of vertebrate species. As of 2006,[19]there are almost 28,000 knownextantspecies, of which almost 27,000 are bony fish, with 970sharks, rays, and chimerasand about 108 hagfish and lampreys. A third of these species fall within the nine largest families; from largest to smallest, these families areCyprinidae,Gobiidae,Cichlidae,Characidae,Loricariidae,Balitoridae,Serranidae,Labridae, andScorpaenidae. About 64 families aremonotypic, containing only one species. The final total of extant species may grow to exceed 32,500.[20]Each year, newspeciesare discovered andscientifically described. As of 2016,[21]there are over 32,000 documented species of bony fish and over 1,100 species of cartilaginous fish. Species are lost throughextinction(seebiodiversity crisis). Recent examples are theChinese paddlefishor thesmooth handfish. Diversity Main article:Diversity of fish  Agnatha (Pacific hagfish)  Chondrichthyes (Horn shark)  Actinopterygii (Brown trout)  Sarcopterygii (Coelacanth)  A relative of the seahorses, theleafy seadragon's appendages allow it to camouflage (in the form ofcrypsis) with the surroundingseaweed.  The psychedelicmandarin dragonetis one of only two animal species known to have blue colouring because of cellular pigment.[22] The term "fish" most precisely describes any non-tetrapodcraniate(i.e. an animal with a skull and in most cases a backbone) that hasgillsthroughout life and whose limbs, if any, are in the shape of fins.[23]Unlike groupings such as birds ormammals, fish are not a singlecladebut aparaphyleticcollection oftaxa, includinghagfishes,lampreys,sharks and rays,ray-finned fish,coelacanths, andlungfish.[24][25]Indeed, lungfish and coelacanths are closer relatives oftetrapods(such as mammals, birds,amphibians, etc.) than of other fish such as ray-finned fish or sharks, so thelast common ancestorof all fish is also an ancestor to tetrapods. As paraphyletic groups are no longer recognised in modernsystematic biology, the use of the term "fish" as a biological group must be avoided. Many types ofaquatic animalscommonly referred to as "fish" are not fish in the sense given above; examples includeshellfish,cuttlefish,starfish,crayfishandjellyfish. In earlier times, even biologists did not make a distinction– sixteenth century natural historians classified alsoseals, whales,amphibians,crocodiles, evenhippopotamuses, as well as a host of aquatic invertebrates, as fish.[26]However, according to the definition above, all mammals, includingcetaceanslike whales and dolphins, are not fish. In some contexts, especially inaquaculture, the true fish are referred to asfinfish(orfin fish) to distinguish them from these other animals. A typical fish isectothermic, has astreamlinedbody for rapid swimming, extracts oxygen from water using gills or uses an accessory breathing organ to breathe atmospheric oxygen, has two sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin, and a tail fin, has jaws, has skin that is usually covered withscales, and lays eggs. Each criterion has exceptions.Tuna,swordfish, and some species ofsharksshowsome warm-blooded adaptations– they can heat their bodies significantly above ambient water temperature.[24]Streamlining and swimming performance varies from fish such as tuna,salmon, andjacksthat can cover 10–20 body-lengths per second to species such aseelsandraysthat swim no more than 0.5 body-lengths per second.[27]Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures.Lungfishhave paired lungs similar to those of tetrapods,gouramishave a structure called thelabyrinth organthat performs a similar function, while many catfish, such asCorydorasextract oxygen via the intestine or stomach.[28]Body shape and the arrangement of the fins is highly variable, covering such seemingly un-fishlike forms asseahorses,pufferfish,anglerfish, andgulpers. Similarly, the surface of the skin may be naked (as inmoray eels), or covered with scales of a variety of different types usually defined asplacoid(typical of sharks and rays),cosmoid(fossil lungfish and coelacanths),ganoid(various fossil fish but also livinggarsandbichirs),cycloid, andctenoid(these last two are found on mostbony fish).[29]There are even fish that live mostly on land or lay their eggs on land near water.[30]Mudskippersfeed and interact with one another on mudflats and go underwater to hide in their burrows.[31]A singleundescribed speciesofPhreatobiushas been called a true "land fish" as this worm-like catfish strictly lives among waterloggedleaf litter.[32][33]Many species live inunderground lakes,underground riversoraquifersand are popularly known ascavefish.[34] Fish range in size from the huge 16-metre (52ft)whale sharkto the tiny 8-millimetre (0.3in)stout infantfish. Fishspeciesdiversity is roughly divided equally between marine (oceanic) andfreshwaterecosystems.Coral reefsin theIndo-Pacificconstitute the center of diversity for marine fishes, whereas continental freshwater fishes are most diverse in largeriver basinsoftropical rainforests, especially theAmazon,Congo, andMekongbasins. More than 5,600 fish species inhabitNeotropicalfreshwaters alone, such thatNeotropical fishesrepresent about 10% of allvertebratespecies on the Earth. Exceptionally rich sites in the Amazon basin, such asCantão State Park, can contain more freshwater fish species than occur in all of Europe.[35] The deepest living fish in the ocean so far found is the Mariana snailfish (Pseudoliparis swirei) which lives at deeps of 8,000 meters (26,200 feet) along the Mariana Trench near Guam.[36] Thediversityof living fish (finfish) is unevenly distributed among the various groups, withteleostsmaking up the bulk of living fishes (96%), and over 50% of allvertebratespecies.[21]The followingcladogram[37]shows theevolutionary relationshipsof all groups of living fishes (with their respective diversity[21]) and the four-limbed vertebrates (tetrapods).  Diversityof various groups of fish (and othervertebrates) through time  Lungfishare the closest living relatives oftetrapods(four-limbed vertebrates).  ThebowfinAmia calvais the sole survivor of thehalecomorphclade. Vertebrates  Jawless fish(118 living species:hagfish,lampreys)  Jawedvertebrates  Cartilaginous fishes(>1,100 living species:sharks,rays,chimaeras)  Bonyfishes Lobe-finfishRhipidistia  Tetrapoda(>30,000 living species:amphibians,mammals,reptiles,birds)    Dipnoi(6 living species:lungfish)     Actinistia(2 living species:coelacanths)   Ray-finfish  Cladistia(14 living species:bichirs,reedfish)  Actinopteri  Chondrostei(27 living species:sturgeons,paddlefish)  Neopterygii Holostei  Ginglymodi(7 living species:gars,alligator gars)    Halecomorphi(1 living species:bowfin)     Teleostei(>32,000 living species)           Anatomy and physiology Further information:Fish anatomyandFish physiology  Organs: 1.Liver, 2.Gas bladder, 3.Roe, 4.Pyloric caeca, 5.Stomach, 6.Intestine Respiration See also:Aquatic respiration Gills  Tunagills inside the head. The fish head is oriented snout-downwards, with the view looking towards the mouth. Most fish exchange gases usinggillson either side of thepharynx. Gills consist of threadlike structures calledfilaments. Each filament contains acapillarynetwork that provides a largesurface areafor exchangingoxygenandcarbon dioxide. Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. In some fish, capillary blood flows in the opposite direction to the water, causingcountercurrent exchange. The gills push the oxygen-poor water out through openings in the sides of the pharynx. Some fish, likesharksandlampreys, possess multiple gill openings. However,bony fishhave a single gill opening on each side. This opening is hidden beneath a protective bony cover called anoperculum. Juvenilebichirshave external gills, a very primitive feature that they share with larvalamphibians. Air breathing Fish from multiple groups can live out of the water for extended periods.Amphibious fishsuch as themudskippercan live and move about on land for up to several days,[dubious–discuss]or live in stagnant or otherwise oxygen depleted water. Many such fish can breathe air via a variety of mechanisms. The skin ofanguillid eelsmay absorb oxygen directly. Thebuccal cavityof theelectric eelmay breathe air. Catfish of the familiesLoricariidae,Callichthyidae, andScoloplacidaeabsorb air through their digestive tracts.[38]Lungfish, with the exception of theAustralian lungfish, andbichirshave paired lungs similar to those oftetrapodsand must surface to gulp fresh air through the mouth and pass spent air out through the gills.Garandbowfinhave a vascularized swim bladder that functions in the same way.Loaches,trahiras, and manycatfishbreathe by passing air through the gut. Mudskippers breathe by absorbing oxygen across the skin (similar to frogs). A number of fish have evolved so-called accessory breathing organs that extract oxygen from the air. Labyrinth fish (such asgouramisandbettas) have alabyrinth organabove the gills that performs this function. A few other fish have structures resembling labyrinth organs in form and function, most notablysnakeheads,pikeheads, and theClariidaecatfish family. Breathing air is primarily of use to fish that inhabit shallow, seasonally variable waters where the water's oxygen concentration may seasonally decline. Fish dependent solely on dissolved oxygen, such as perch andcichlids, quickly suffocate, while air-breathers survive for much longer, in some cases in water that is little more than wet mud. At the most extreme, some air-breathing fish are able to survive in damp burrows for weeks without water, entering a state ofaestivation(summertime hibernation) until water returns. Air breathing fish can be divided into obligate air breathers and facultative air breathers. Obligate air breathers, such as theAfrican lungfish,mustbreathe air periodically or they suffocate. Facultative air breathers, such as the catfishHypostomus plecostomus, only breathe air if they need to and will otherwise rely on their gills for oxygen. Most air breathing fish are facultative air breathers that avoid the energetic cost of rising to the surface and the fitness cost of exposure to surface predators.[38] Circulation  Didactic modelof a fish heart Fish have aclosed-loop circulatory system. Theheartpumps the blood in a single loop throughout the body. In most fish, the heart consists of four parts, including two chambers and an entrance and exit.[39]The first part is thesinus venosus, a thin-walled sac that collects blood from the fish'sveinsbefore allowing it to flow to the second part, theatrium, which is a large muscular chamber. The atrium serves as a one-way antechamber, sends blood to the third part,ventricle. The ventricle is another thick-walled, muscular chamber and it pumps the blood, first to the fourth part,bulbus arteriosus, a large tube, and then out of the heart. The bulbus arteriosus connects to theaorta, through which blood flows to the gills for oxygenation. Digestion Jaws allow fish to eat a wide variety of food, including plants and other organisms. Fish ingest food through the mouth and break it down in theesophagus. In the stomach, food is further digested and, in many fish, processed in finger-shaped pouches calledpyloric caeca, which secrete digestiveenzymesand absorb nutrients. Organs such as theliverandpancreasadd enzymes and various chemicals as the food moves through the digestive tract. The intestine completes the process of digestion and nutrient absorption. Excretion As with many aquatic animals, most fish release their nitrogenous wastes asammonia. Some of the wastesdiffusethrough the gills. Blood wastes arefilteredby thekidneys. Saltwater fish tend to lose water because ofosmosis. Their kidneys return water to the body. The reverse happens infreshwater fish: they tend to gain water osmotically. Their kidneys produce dilute urine for excretion. Some fish have specially adapted kidneys that vary in function, allowing them to move from freshwater to saltwater. Scales Main article:Fish scale The scales of fish originate from themesoderm(skin); they may be similar in structure to teeth. Sensory and nervous system  Dorsal view of the brain of therainbow trout Central nervous system Fish typically have quite small brains relative to body size compared with other vertebrates, typically one-fifteenth the brain mass of a similarly sized bird or mammal.[40]However, some fish have relatively large brains, most notablymormyridsandsharks, which have brains about as massive relative to body weight as birds andmarsupials.[41] Fish brains are divided into several regions. At the front are theolfactory lobes, a pair of structures that receive and process signals from thenostrilsvia the twoolfactory nerves.[40]The olfactory lobes are very large in fish that hunt primarily by smell, such as hagfish, sharks, and catfish. Behind the olfactory lobes is the two-lobedtelencephalon, the structural equivalent to thecerebruminhigher vertebrates. In fish the telencephalon is concerned mostly witholfaction.[40]Together these structures form the forebrain. Connecting the forebrain to the midbrain is thediencephalon(in the diagram, this structure is below the optic lobes and consequently not visible). The diencephalon performs functions associated withhormonesandhomeostasis.[40]Thepineal bodylies just above the diencephalon. This structure detects light, maintainscircadianrhythms, and controls color changes.[40] Themidbrain(or mesencephalon) contains the twooptic lobes. These are very large in species that hunt by sight, such asrainbow troutandcichlids.[40] The hindbrain (ormetencephalon) is particularly involved in swimming and balance.[40]The cerebellum is a single-lobed structure that is typically the biggest part of the brain.[40]Hagfish andlampreyshave relatively small cerebellae, while themormyridcerebellum is massive and apparently involved in theirelectrical sense.[40] The brain stem (ormyelencephalon) is the brain's posterior.[40]As well as controlling some muscles and body organs, in bony fish at least, the brain stem governsrespirationandosmoregulation.[40] Sense organs Main article:Sensory systems in fish Most fish possess highly developed sense organs. Nearly all daylight fish have color vision that is at least as good as a human's (seevision in fishes). Many fish also have chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears, many fish may not hear very well. Most fish have sensitive receptors that form thelateral line system, which detects gentle currents and vibrations, and senses the motion of nearby fish and prey.[42]The sense information obtained from the lateral line system can be considered both a sense oftouchandhearing.Blind cave fishnavigate almost entirely through the sensations from their lateral line system.[43]Some fish, such as catfish and sharks, have theampullae of Lorenzini,electroreceptorsthat detect weak electric currents on the order of millivolt.[44]Other fish, like the South American electric fishesGymnotiformes, can produce weak electric currents, which they use in navigation and social communication. Fish orient themselves using landmarks and may use mental maps based on multiple landmarks or symbols. Fish behavior in mazes reveals that they possess spatial memory and visual discrimination.[45] Vision Main article:Vision in fishes Visionis an importantsensory systemfor most species of fish. Fish eyes are similar to those ofterrestrialvertebrateslikebirdsand mammals, but have a moresphericallens. Theirretinasgenerally have bothrodsandcones(forscotopicandphotopic vision), and most species havecolour vision. Some fish can seeultravioletand some can seepolarized light. Amongstjawless fish, thelampreyhas well-developed eyes, while thehagfishhas only primitiveeyespots.[46]Fish vision showsadaptationto their visual environment, for exampledeep sea fisheshave eyes suited to the dark environment. Hearing See also:Hearing in fish Hearingis an important sensory system for most species of fish. Fish sense sound using theirlateral linesand theirears. Cognition Further information:Fish intelligence New research has expanded preconceptions about the cognitive capacities of fish. For example,manta rayshave exhibited behavior linked toself-awarenessinmirror testcases. Placed in front of a mirror, individual rays engaged in contingency testing, that is, repetitive behavior aiming to check whether their reflection's behavior mimics their body movement.[47] Wrasseshave also passed the mirror test in a 2018 scientific study.[48][49] Cases of tool use have also been noticed, notably in theChoerodonfamily, inarcherfishandAtlantic cod.[50] Capacity for pain Further information:Pain in fish Experiments done by William Tavolga provide evidence that fish havepainand fear responses. For instance, in Tavolga's experiments,toadfishgrunted when electrically shocked and over time they came to grunt at the mere sight of an electrode.[51] In 2003, Scottish scientists at theUniversity of Edinburghand the Roslin Institute concluded that rainbow trout exhibit behaviors often associated withpainin other animals.Beevenomandacetic acidinjected into the lips resulted in fish rocking their bodies and rubbing their lips along the sides and floors of their tanks, which the researchers concluded were attempts to relieve pain, similar to what mammals would do.[52][53]Neurons fired in a pattern resembling human neuronal patterns.[53] Professor James D. Rose of theUniversity of Wyomingclaimed the study was flawed since it did not provide proof that fish possess "conscious awareness, particularly a kind of awareness that is meaningfully like ours".[54]Rose argues that since fish brains are so different from human brains, fish are probably not conscious in the manner humans are, so that reactions similar to human reactions to pain instead have other causes. Rose had published a study a year earlier arguing that fish cannot feel pain because their brains lack aneocortex.[55]However, animal behavioristTemple Grandinargues that fish could still have consciousness without a neocortex because "different species can use different brain structures and systems to handle the same functions."[53] Animal welfare advocates raise concerns about the possiblesufferingof fish caused by angling. Some countries, such as Germany, have banned specific types of fishing, and the BritishRSPCAnow formally prosecutes individuals who are cruel to fish.[56] Emotion In 2019, scientists have shown that members of themonogamousspeciesAmatitlania siquiaexhibit pessimistic behavior when they are prevented from being with their partner.[57] Muscular system Main article:Fish locomotion  The anatomy ofLampanyctodes hectoris(1)operculum (gill cover), (2)lateral line, (3)dorsal fin, (4)fat fin, (5)caudal peduncle, (6)caudal fin, (7)anal fin, (8)photophores, (9)pelvic fins (paired), (10)pectoral fins (paired)  Swim bladder of a rudd (Scardinius erythrophthalmus) Most fish move by alternately contracting paired sets of muscles on either side of the backbone. These contractions form S-shaped curves that move down the body. As each curve reaches the back fin, backward force is applied to the water, and in conjunction with the fins, moves the fish forward. The fish's fins function like an airplane's flaps. Fins also increase the tail's surface area, increasing speed. The streamlined body of the fish decreases the amount of friction from the water. Since body tissue is denser than water, fish must compensate for the difference or they will sink. Many bony fish have an internal organ called aswim bladderthat adjusts their buoyancy through manipulation of gases. Endothermy Although most fish are exclusivelyectothermic, there are exceptions. The only known bony fishes (infraclassTeleostei) that exhibitendothermyare in the suborderScombroidei– which includes thebillfishes, tunas, and thebutterfly kingfish, abasalspecies of mackerel[58]– and also theopah. The opah, alampriform, was demonstrated in 2015 to utilize "whole-body endothermy", generating heat with its swimming muscles to warm its body while countercurrent exchange (as in respiration) minimizes heat loss.[59]It is able to actively hunt prey such as squid and swim for long distances due to the ability to warm its entire body, including its heart,[60]which is a trait typically found in only mammals and birds (in the form ofhomeothermy). In the cartilaginous fishes (classChondrichthyes), sharks of the familiesLamnidae(porbeagle, mackerel, salmon, and great white sharks) andAlopiidae(thresher sharks) exhibit endothermy. The degree of endothermy varies from the billfishes, which warm only their eyes and brain, to thebluefin tunaand theporbeagle shark, which maintain body temperatures in excess of 20°C (68°F) above ambient water temperatures.[58] Endothermy, though metabolically costly, is thought to provide advantages such as increased muscle strength, higher rates of centralnervous systemprocessing, and higher rates ofdigestion. Reproductive system Further information:Fish reproductionandSpawn (biology)  Ovary of fish (Corumbatá) Fish reproductive organs includetesticlesandovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused.[61]There may also be a range of secondary organs that increase reproductive fitness. In terms ofspermatogoniadistribution, the structure ofteleoststestes has two types: in the most common, spermatogonia occur all along theseminiferous tubules, while inatherinomorphfish they are confined to thedistalportion of these structures. Fish can present cystic or semi-cysticspermatogenesisin relation to the release phase of germ cells in cysts to the seminiferous tubuleslumen.[61] Fish ovaries may be of three types: gymnovarian, secondary gymnovarian or cystovarian. In the first type, theoocytesare released directly into thecoelomiccavity and then enter theostium, then through theoviductand are eliminated. Secondary gymnovarian ovaries shedovainto the coelom from which they go directly into the oviduct. In the third type, the oocytes are conveyed to the exterior through the oviduct.[62]Gymnovaries are the primitive condition found inlungfish,sturgeon, andbowfin. Cystovaries characterize most teleosts, where the ovary lumen has continuity with the oviduct.[61]Secondary gymnovaries are found insalmonidsand a few other teleosts. Oogoniadevelopment in teleosts fish varies according to the group, and the determination of oogenesis dynamics allows the understanding of maturation and fertilization processes. Changes in thenucleus, ooplasm, and the surrounding layers characterize the oocyte maturation process.[61] Postovulatoryfolliclesare structures formed after oocyte release; they do not haveendocrinefunction, present a wide irregular lumen, and are rapidly reabsorbed in a process involving theapoptosisof follicular cells. A degenerative process calledfollicular atresiareabsorbs vitellogenic oocytes not spawned. This process can also occur, but less frequently, in oocytes in other development stages.[61] Some fish, like theCalifornia sheephead, arehermaphrodites, having both testes and ovaries either at different phases in their life cycle or, as inhamlets, have them simultaneously. Over 97% of all known fish areoviparous,[63]that is, the eggs develop outside the mother's body. Examples of oviparous fish includesalmon,goldfish,cichlids,tuna, andeels. In the majority of these species, fertilisation takes place outside the mother's body, with the male and female fish shedding theirgametesinto the surrounding water. However, a few oviparous fish practice internal fertilization, with the male using some sort ofintromittent organto deliver sperm into the genital opening of the female, most notably the oviparous sharks, such as thehorn shark, and oviparous rays, such asskates. In these cases, the male is equipped with a pair of modifiedpelvic finsknown asclaspers. Marine fish can produce high numbers of eggs which are often released into the open water column. The eggs have an average diameter of 1 millimetre (0.04in).  Egg oflamprey  Egg ofcatshark(mermaids' purse)  Egg ofbullhead shark  Egg ofchimaera The newly hatched young of oviparous fish are calledlarvae. They are usually poorly formed, carry a largeyolk sac(for nourishment), and are very different in appearance from juvenile and adult specimens. The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termedmetamorphosis) to become juveniles. During this transition larvae must switch from their yolk sac to feeding onzooplanktonprey, a process which depends on typically inadequate zooplankton density, starving many larvae. Inovoviviparousfish the eggs develop inside the mother's body after internal fertilization but receive little or no nourishment directly from the mother, depending instead on theyolk. Each embryo develops in its own egg. Familiar examples of ovoviviparous fish includeguppies,angel sharks, andcoelacanths. Some species of fish areviviparous. In such species the mother retains the eggs and nourishes the embryos. Typically, viviparous fish have a structure analogous to theplacentaseen inmammalsconnecting the mother's blood supply with that of the embryo. Examples of viviparous fish include thesurf-perches,splitfins, andlemon shark. Some viviparous fish exhibitoophagy, in which the developing embryos eat other eggs produced by the mother. This has been observed primarily among sharks, such as theshortfin makoandporbeagle, but is known for a few bony fish as well, such as thehalfbeakNomorhamphus ebrardtii.[64]Intrauterine cannibalismis an even more unusual mode of vivipary, in which the largest embryos eat weaker and smaller siblings. This behavior is also most commonly found among sharks, such as thegrey nurse shark, but has also been reported forNomorhamphus ebrardtii.[64] Aquaristscommonly refer to ovoviviparous and viviparous fish aslivebearers. Acoustic communication See also:Acoustic communication in aquatic animals Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another. The production of sounds as a means of communication among fish is most often used in the context of feeding, aggression or courtship behaviour.[3]The sounds emitted can vary depending on the species and stimulus involved. Fish can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder.[65] Stridulatory  French grunts –Haemulon flavolineatum There are some species of fish that can produce sounds by rubbing or grinding their bones together. These noises produced by bone-on-bone interactions are known as 'stridulatory sounds'.[65] An example of this is seen inHaemulon flavolineatum, a species commonly referred to as the 'French grunt fish', as it produces a grunting noise by grinding its teeth together.[65]This behaviour is most pronounced when theH. flavolineatumis in distress situations.[65]The grunts produced by this species of fishes generate a frequency of approximately 700Hz, and last approximately 47 milliseconds.[65]TheH. flavolineatumdoes not emit sounds with frequencies greater than 1000Hz, and does not detect sounds that have frequencies greater than 1050Hz.[65] In a study conducted by Oliveira et al. (2014), the longsnout seahorse,Hippocampus reidi, was recorded producing two different categories of sounds; 'clicks' and 'growls'. The sounds emitted by theH. reidiare accomplished by rubbing their coronet bone across the grooved section of their neurocranium.[66]'Clicking' sounds were found to be primarily produced during courtship and feeding, and the frequencies of clicks were within the range of 50Hz-800Hz.[67]The frequencies were noted to be on the higher end of the range during spawning periods, when the female and male fishes were less than fifteen centimeters apart.[67]Growl sounds were produced when theH. reidiencountered stressful situations, such as handling by researchers.[67]The 'growl' sounds consist of a series of sound pulses and are emitted simultaneously with body vibrations.[67] Non-stridulatory  Oyster toadfish Some fish species create noise by engaging specialized muscles that contract and cause swimbladder vibrations. Oyster toadfishproduce loud grunting sounds by contracting muscles located along the sides of their swim bladder, known as sonic muscles[68]Female and male toadfishes emit short-duration grunts, often as a fright response.[69]In addition to short-duration grunts, male toadfishes produce "boat whistle calls".[70]These calls are longer in duration, lower in frequency, and are primarily used to attract mates.[70]The sounds emitted by theO. taohave frequency range of 140Hz to 260Hz.[70]The frequencies of the calls depend on the rate at which the sonic muscles contract.[71][68] The red drum,Sciaenops ocellatus, produces drumming sounds by vibrating its swimbladder.[72]Vibrations are caused by the rapid contraction of sonic muscles that surround the dorsal aspect of the swimbladder.[72]These vibrations result in repeated sounds with frequencies that range from 100 to >200Hz.[72]TheS. ocellatuscan produce different calls depending on the stimuli involved.[72]The sounds created in courtship situations are different from those made during distressing events such as predatorial attacks.[72]Unlike the males of theS. ocellatusspecies, the females of this species do not produce sounds and lack sound-producing (sonic) muscles.[72] Diseases Main article:Fish diseases and parasites Like other animals, fish suffer from diseases and parasites. To prevent disease they have a variety of defenses.Non-specificdefenses include the skin and scales, as well as the mucus layer secreted by theepidermisthat traps and inhibits the growth ofmicroorganisms. Ifpathogensbreach these defenses, fish can develop aninflammatory responsethat increases blood flow to the infected region and deliverswhite blood cellsthat attempt to destroy pathogens. Specific defenses respond to particular pathogens recognised by the fish's body, i.e., animmune response.[73]In recent years,vaccineshave become widely used in aquaculture and also with ornamental fish, for examplefurunculosisvaccines in farmedsalmonandkoi herpes virusinkoi.[74][75] Some species usecleaner fishto remove external parasites. The best known of these are thebluestreak cleaner wrassesof the genusLabroidesfound oncoral reefsin theIndianandPacificoceans. These small fish maintain so-called "cleaning stations" where other fish congregate and perform specific movements to attract the attention of the cleaners.[76]Cleaning behaviors have been observed in a number of fish groups, including an interesting case between two cichlids of the same genus,Etroplus maculatus, the cleaner, and the much largerEtroplus suratensis.[77] Immune system Immune organs vary by type of fish.[78]In thejawless fish(lampreys and hagfish), truelymphoidorgans are absent. These fish rely on regions oflymphoid tissuewithin other organs to produce immune cells. For example,erythrocytes,macrophagesandplasma cellsare produced in the anterior kidney (orpronephros) and some areas of the gut (wheregranulocytesmature.) They resemble primitivebone marrowin hagfish.Cartilaginous fish(sharks and rays) have a more advanced immune system. They have three specialized organs that are unique toChondrichthyes; the epigonal organs (lymphoid tissue similar to mammalian bone) that surround the gonads, theLeydig's organwithin the walls of their esophagus, and aspiral valvein their intestine. These organs house typical immune cells (granulocytes, lymphocytes and plasma cells). They also possess an identifiablethymusand a well-developedspleen(their most important immune organ) where variouslymphocytes, plasma cells and macrophages develop and are stored.Chondrosteanfish (sturgeons, paddlefish, and bichirs) possess a major site for the production of granulocytes within a mass that is associated with themeninges(membranes surrounding the central nervous system.) Their heart is frequently covered with tissue that contains lymphocytes,reticular cellsand a small number ofmacrophages. The chondrostean kidney is an importanthemopoieticorgan; where erythrocytes, granulocytes, lymphocytes and macrophages develop. Like chondrostean fish, the major immune tissues of bony fish (orteleostei) include the kidney (especially the anterior kidney), which houses many different immune cells.[79]In addition, teleost fish possess a thymus, spleen and scattered immune areas within mucosal tissues (e.g. in the skin, gills, gut and gonads). Much like the mammalian immune system, teleost erythrocytes, neutrophils and granulocytes are believed to reside in the spleen whereas lymphocytes are the major cell type found in the thymus.[80][81]In 2006, a lymphatic system similar to that in mammals was described in one species of teleost fish, thezebrafish. Although not confirmed as yet, this system presumably will be where naive (unstimulated)T cellsaccumulate while waiting to encounter anantigen.[82] B and T lymphocytes bearingimmunoglobulinsandT cell receptors, respectively, are found in all jawed fishes. Indeed, theadaptive immune systemas a wholeevolvedin an ancestor of all jawed vertebrates.[83] Conservation The 2006IUCNRed Listnames 1,173 fish species that are threatened with extinction.[84]Included are species such asAtlantic cod,[85]Devil's Hole pupfish,[86]coelacanths,[87]andgreat white sharks.[88]Because fish live underwater they are more difficult to study than terrestrial animals and plants, and information about fish populations is often lacking. However, freshwater fish seem particularly threatened because they often live in relatively small water bodies. For example, theDevil's Hole pupfishoccupies only a single 3 by 6 metres (10 by 20ft) pool.[89] Overfishing  Whale sharks, the largest species of fish, are classified asvulnerable. Main article:Overfishing Overfishing is a major threat to edible fish such as cod andtuna.[90][91]Overfishing eventually causespopulation(known asstock) collapse because the survivors cannot produce enough young to replace those removed. Suchcommercial extinctiondoes not mean that the species is extinct, merely that it can no longer sustain a fishery. One well-studied example of fishery collapse is thePacific sardineSadinops sagax caeruluesfishery off the California coast. From a 1937 peak of 790,000 long tons (800,000t) the catch steadily declined to only 24,000 long tons (24,000t) in 1968, after which the fishery was no longer economically viable.[92] The main tension betweenfisheries scienceand thefishing industryis that the two groups have different views on the resiliency of fisheries to intensive fishing. In places such as Scotland, Newfoundland, and Alaska the fishing industry is a major employer, so governments are predisposed to support it.[93][94]On the other hand, scientists and conservationists push for stringent protection, warning that many stocks could be wiped out within fifty years.[95][96] Habitat destruction See also:Environmental impact of fishing A key stress on both freshwater and marine ecosystems is habitat degradation includingwater pollution, the building of dams, removal of water for use by humans, and the introduction ofexoticspecies.[97]An example of a fish that has become endangered because of habitat change is thepallid sturgeon, a North American freshwater fish that lives in rivers damaged by human activity.[98] Exotic species Introduction ofnon-nativespecies has occurred in many habitats. One of the best studied examples is the introduction ofNile perchintoLake Victoriain the 1960s. Nile perch gradually exterminated the lake's 500endemiccichlidspecies. Some of them survive now in captive breeding programmes, but others are probably extinct.[99]Carp,snakeheads,[100]tilapia,European perch,brown trout,rainbow trout, andsea lampreysare other examples of fish that have caused problems by being introduced into alien environments. Importance to humans Economic Main articles:Fishing industry,Aquaculture, andFish farming  These fish-farming ponds were created as acooperativeproject in a rural village. Throughout history, humans have utilizedfish as a food source. Historically and today, most fishproteinhas come by means of catching wild fish. However, aquaculture, or fish farming, which has been practiced since about 3,500 BCE. in China,[101]is becoming increasingly important in many nations. Overall, about one-sixth of the world's protein is estimated to be provided by fish.[102]That proportion is considerably elevated in somedeveloping nationsand regions heavily dependent on the sea. In a similar manner, fish have been tied to trade.  Fish counter display at theOulu Market HallinOulu, Finland. Catching fish for the purpose of food or sport is known asfishing, while the organized effort by humans to catch fish is called afishery. Fisheries are a huge global business and provide income for millions of people.[102]The annual yield from all fisheries worldwide is about 154 million tons,[103]with popular species includingherring,cod,anchovy,tuna,flounder, andsalmon. However, the term fishery is broadly applied, and includes more organisms than just fish, such asmollusksandcrustaceans, which are often called "fish" when used as food. Recreation  ABengalifish vendor Main articles:Fishkeeping,Recreational fishing, andAngling Fishkeeping Fish have been recognized as a source of beauty for almost as long as used for food, appearing incave art, being raised asornamental fishin ponds, and displayed inaquariumsin homes, offices, or public settings. Recreational fishing Recreational fishingis fishing primarily for pleasure or competition; it can be contrasted withcommercial fishing, which is fishing for profit, orartisanal fishing, which is fishing primarily for food. The most common form of recreational fishing is done with arod,reel,line,hooks, and any one of a wide range ofbaits. Recreational fishing is particularly popular in North America and Europe and state, provincial, and federal government agencies actively management target fish species.[104][105]Angling is a method of fishing, specifically the practice of catching fish by means of an "angle" (hook). Anglers must select the right hook,castaccurately, and retrieve at the right speed while considering water and weather conditions, species, fish response, time of the day, and other factors. Culture Main article:Fish in culture  AvatarofVishnuas aMatsya Fish themes have symbolic significance in many religions. In ancientMesopotamia, fish offerings were made to the gods from the very earliest times.[106]Fish were also a major symbol ofEnki, the god of water.[106]Fish frequently appear as filling motifs incylinder sealsfrom theOld Babylonian(c.1830 BC –c.1531 BC) andNeo-Assyrian(911–609 BC) periods.[106]Starting during theKassite Period(c.1600 BC –c.1155 BC) and lasting until the earlyPersian Period(550–30 BC), healers and exorcists dressed in ritual garb resembling the bodies of fish.[106]During theSeleucid Period(312–63 BC), the legendary Babylonianculture heroOannes, described byBerossus, was said to have dressed in the skin of a fish.[106]Fish were sacred to the Syrian goddessAtargatis[107]and, during her festivals, only her priests were permitted to eat them.[107]  Theichthusis a Christian symbol of a fish signifying that the person who uses it is a Christian.[107][108] In theBook of Jonah, a work of Jewish literature probably written in the fourth century BC, the central figure, aprophetnamedJonah, is swallowed by a giant fish after being thrown overboard by the crew of the ship he is travelling on.[109][110][111]The fish later vomits Jonah out on shore after three days.[109][110][111]This book was later included as part of theHebrew Bible, or ChristianOld Testament,[112][113]and a version of the story it contains is summarized inSurah37:139-148 of theQuran.[114]Early Christiansused theichthys, a symbol of a fish, to represent Jesus,[107][108]because the Greek word for fish, ΙΧΘΥΣ Ichthys, could be used as an acronym for "Ίησοῦς Χριστός, Θεοῦ Υἱός, Σωτήρ" (Iesous Christos, Theou Huios, Soter), meaning "Jesus Christ, Son of God, Saviour".[107][108]Thegospelsalso refer to "fishers of men"[115]andfeeding the multitude. In thedhammaofBuddhism, the fish symbolize happiness as they have complete freedom of movement in the water. Often drawn in the form ofcarpwhich are regarded in the Orient as sacred on account of their elegant beauty, size and life-span. Among thedeitiessaid to take the form of a fish areIka-Roaof thePolynesians,Dagonof various ancientSemitic peoples, the shark-gods ofHawaiʻiandMatsyaof the Hindus. TheastrologicalsymbolPiscesis based on a constellation of thesame name, but there is also a second fish constellation in the night sky,Piscis Austrinus.[116] Fish feature prominently in art and literature, in movies such asFinding Nemoand books such asThe Old Man and the Sea. Large fish, particularly sharks, have frequently been the subject ofhorror moviesandthrillers, most notably the novelJaws, which spawned a series of films of thesame namethat in turn inspired similar films or parodies such asShark TaleandSnakehead Terror. Piranhas are shown in a similar light to sharks in films such asPiranha; however, contrary to popular belief, thered-bellied piranhais actually a generally timid scavenger species that is unlikely to harm humans.[117]Legends of half-human, half-fishmermaidshave featured in folklore, including the stories ofHans Christian Andersen. Terminology "Fish" or "fishes" Though often used interchangeably, in biology these words have different meanings.Fishis used as a singular noun, or as a plural to describe multiple individuals from a single species.Fishesis used to describe different species or species groups.[118][119][120]Thus a pond would be said to contain 120 fish if all were from a single species or 120 fishes if these included a mix of several species. The distinction is similar to that between people and peoples. "True fish" or "finfish" In biology, the termfishis most strictly used to describe any animal with abackbone,gillsthroughout life, and limbs (if any) in the shape offins.[23]Many types ofaquatic animalswith common names ending in "fish" are not fish in thissense; examples includeshellfish,cuttlefish,starfish,crayfishandjellyfish. In earlier times, even biologists did not make a distinction– sixteenth century natural historians classified alsoseals, whales,amphibians,crocodiles, evenhippopotamuses, as well as a host of aquatic invertebrates, as fish.[26] In fisheries, the termfishis used as a collective term, and includesmollusks,crustaceansand anyaquatic animalwhich is harvested.[121] The strict biological definition of a fish, above, is sometimes called atrue fish. True fish are also referred to asfinfishorfin fishto distinguish them from other aquatic life harvested in fisheries or aquaculture. "Shoal" or "school" Main article:Shoaling and schooling  Thesegoldband fusiliersareschoolingbecause their swimming is synchronised. An assemblage of fish merely using some localised resource such as food or nesting sites is known simply as anaggregation. When fish come together in an interactive, social grouping, then they may be forming either ashoalor aschooldepending on the degree of organisation. Ashoalis a loosely organised group where each fish swims and forages independently but is attracted to other members of the group and adjusts its behaviour, such as swimming speed, so that it remains close to the other members of the group.Schoolsof fish are much more tightly organised, synchronising their swimming so that all fish move at the same speed and in the same direction. Shoaling and schooling behaviour is believed to provide a variety of advantages.[122] Examples: Cichlids congregating atlekkingsites form anaggregation. Many minnows and characins formshoals. Anchovies, herrings and silversides are classic examples ofschoolingfish. The most common collective nouns for a group of fish in general are school and shoal. Both the words have evolved from the same common Dutch root 'schole' meaning a troop or crowd. While the words "school" and "shoal" have different meanings within biology, the distinctions are often ignored by non-specialists who treat the words assynonyms. Thus speakers ofBritish Englishcommonly use "shoal" to describe any grouping of fish, and speakers ofAmerican Englishcommonly use "school" just as loosely.[123]

This article is about the species that is commonly kept as a pet. For the cat family, seeFelidae. For other uses, seeCat (disambiguation). "Cats" redirects here. For other uses, seeCats (disambiguation). Thecat(Felis catus) is adomesticspeciesof smallcarnivorousmammal.[1][2]It is the only domesticated species in the familyFelidaeand is often referred to as thedomestic catto distinguish it from the wild members of the family.[4]A cat can either be ahouse cat, afarm cator aferal cat; the latter ranges freely and avoids human contact.[5]Domestic cats are valued by humans for companionship and their ability to killrodents. About 60cat breedsare recognized by variouscat registries.[6] Cat Temporal range: 9,500 years ago – present Various types of cat Conservation status Domesticated Scientific classificationKingdom:AnimaliaPhylum:ChordataClass:MammaliaOrder:CarnivoraSuborder:FeliformiaFamily:FelidaeSubfamily:FelinaeGenus:FelisSpecies: F.catus[1] Binomial nameFelis catus[1] Linnaeus,1758[2] Synonyms Catus domesticusErxleben, 1777[3] F. angorensisGmelin, 1788 F. vulgarisFischer, 1829 The cat is similar inanatomyto the other felid species: it has a strong flexible body, quickreflexes, sharp teeth andretractable clawsadapted to killing small prey. Itsnight visionand sense of smell are well developed.Cat communicationincludesvocalizationslikemeowing,purring, trilling, hissing,growlingand grunting as well ascat-specific body language. Apredatorthat is most active at dawn and dusk (crepuscular), the cat is a solitary hunter but asocial species. It can hear sounds too faint or too high infrequencyfor human ears, such as those made bymiceand other small mammals.[7]Cats also secrete and perceivepheromones.[8] Female domestic cats can have kittens from spring to late autumn, with litter sizes often ranging from two to five kittens.[9]Domestic cats are bred and shown at events as registeredpedigreed cats, a hobby known ascat fancy.Population controlof cats may be effected byspayingandneutering, but their proliferation and the abandonment of pets has resulted in large numbers of feral cats worldwide, contributing to the extinction of entire bird, mammal, and reptile species.[10] It was long thought that cat domestication began inancient Egypt, wherecats were veneratedfrom around 3100 BC,[11][12]but recent advances in archaeology and genetics have shown that their domestication occurred inWestern Asiaaround 7500 BC.[13] As of 2021,there were an estimated 220 million owned and 480 million stray cats in the world.[14][15]As of 2017,the domestic cat was the second most popular pet in the United States, with 95.6 million cats owned[16][17][18]and around 42 million households own at least one cat.[19]In the United Kingdom, 26% of adults have a cat with an estimated population of 10.9 million pet cats as of 2020.[20] Contents Etymology and naming The origin of the English wordcat,Old Englishcatt, is thought to be theLate Latinwordcattus, which was first used at the beginning of the 6th century.[21]It was suggested that the word 'cattus' is derived from anEgyptianprecursor ofCopticϣⲁⲩšau, "tomcat", or its feminine form suffixed with-t.[22]The Late Latin word may be derived from anotherAfro-Asiatic[23]orNilo-Saharanlanguage. TheNubianwordkaddîska"wildcat" andNobiinkadīsare possible sources or cognates.[24]The Nubian word may be a loan fromArabicقَطّ‎qaṭṭ~قِطّqiṭṭ. It is "equally likely that the forms might derive from an ancient Germanic word, imported into Latin and thence to Greek and to Syriac and Arabic".[25]The word may be derived from Germanic and Northern European languages, and ultimately be borrowed fromUralic, cf.Northern Samigáđfi, "femalestoat", andHungarianhölgy, "lady, female stoat"; fromProto-Uralic*käďwä, "female (of a furred animal)".[26] The Englishpuss, extended aspussyandpussycat, is attested from the 16th century and may have been introduced fromDutchpoesor fromLow Germanpuuskatte, related toSwedishkattepus, orNorwegianpus,pusekatt. Similar forms exist in LithuanianpuižėandIrishpuisínorpuiscín. The etymology of this word is unknown, but it may have simplyarisen from a soundused to attract a cat.[27][28] A male cat is called atomortomcat[29](or agib,[30]if neutered). Anunspayedfemale is called aqueen,[31](or amolly,[32]if spayed), especially in a cat-breeding context. A juvenile cat is referred to as akitten. InEarly Modern English, the wordkittenwas interchangeable with the now-obsolete wordcatling.[33]A group of cats can be referred to as aclowderor aglaring.[34] Taxonomy Thescientific nameFelis catuswas proposed byCarl Linnaeusin 1758 for a domestic cat.[1][2]Felis catus domesticuswas proposed byJohann Christian Polycarp Erxlebenin 1777.[3]Felis daemonproposed byKonstantin Alekseevich Satuninin 1904 was a black cat from theTranscaucasus, later identified as a domestic cat.[35][36] In 2003, theInternational Commission on Zoological Nomenclatureruled that the domestic cat is a distinct species, namelyFelis catus.[37][38]In 2007, it was considered asubspecies,F. silvestris catus, of theEuropean wildcat(F. silvestris) following results ofphylogeneticresearch.[39][40]In 2017, the IUCN Cat Classification Taskforce followed the recommendation of the ICZN in regarding the domestic cat as a distinct species,Felis catus.[41] Evolution Main article:Cat evolution  Skulls of a wildcat (top left), a housecat (top right), and a hybrid between the two. (bottom center) The domestic cat is a member of the Felidae, afamilythat had acommon ancestorabout 10–15 million years ago.[42]ThegenusFelisdivergedfrom other Felidae around 6–7 million years ago.[43]Results ofphylogeneticresearch confirm that the wildFelisspecies evolved throughsympatricorparapatric speciation, whereas the domestic cat evolved throughartificial selection.[44]The domesticated cat and its closest wild ancestor arediploidand both possess 38chromosomes[45]and roughly 20,000 genes.[46]Theleopard cat(Prionailurus bengalensis) wastamedindependently in China around 5500 BC. This line of partially domesticated cats leaves no trace in the domestic cat populations of today.[47] Domestication See also:Evolution of the domesticated cat  A cat eating a fish under a chair, amuralin an Egyptian tomb dating to the 15th century BC The earliest known indication for thetamingof anAfrican wildcat(F. lybica) wasexcavatedclose by a humanNeolithicgrave inShillourokambos, southernCyprus, dating to about 7500–7200 BC. Since there is no evidence of native mammalianfaunaon Cyprus, the inhabitants of this Neolithic village most likely brought the cat and other wild mammals to the island from theMiddle Easternmainland.[48]Scientists therefore assume that African wildcats were attracted to early human settlements in theFertile Crescentby rodents, in particular thehouse mouse(Mus musculus), and were tamed by Neolithic farmers. Thismutualrelationship between early farmers and tamed cats lasted thousands of years. Asagricultural practicesspread, so did tame and domesticated cats.[13][6]Wildcats of Egypt contributed to the maternalgene poolof the domestic cat at a later time.[49] The earliest known evidence for the occurrence of the domestic cat inGreecedates to around 1200 BC. Greek,Phoenician,CarthaginianandEtruscantraders introduced domestic cats to southern Europe.[50]During theRoman Empirethey were introduced toCorsicaandSardiniabefore the beginning of the 1st millennium.[51]By the 5th century BC, they were familiar animals around settlements inMagna GraeciaandEtruria.[52]By the end of the Roman Empire in the 5th century, the Egyptian domestic cat lineage had arrived in aBaltic Seaport in northernGermany.[49] During domestication, cats have undergone only minor changes in anatomy and behavior, and they are still capable of surviving in the wild. Several natural behaviors and characteristics of wildcats may havepre-adaptedthem for domestication as pets. These traits include their small size, social nature, obvious body language, love of play and relatively high intelligence. CaptiveLeoparduscats may also display affectionate behavior toward humans but were not domesticated.[53]House cats often mate with feral cats,[54]producing hybrids such as theKellas catinScotland.[55]Hybridisation between domestic and other Felinae speciesis also possible.[56] Development ofcat breedsstarted in the mid 19th century.[57]An analysis of the domestic catgenomerevealed that the ancestral wildcat genome was significantly altered in the process of domestication, as specificmutationswere selected to develop cat breeds.[58]Most breeds are founded on random-bred domestic cats.Genetic diversityof these breeds varies between regions, and is lowest in purebred populations, which show more than 20 deleteriousgenetic disorders.[59] Characteristics Main article:Cat anatomy Size  Diagram of the generalanatomyof a male domestic cat The domestic cat has a smallerskulland shorter bones than theEuropean wildcat.[60]It averages about 46cm (18in) in head-to-body length and 23–25cm (9–10in) in height, with about 30cm (12in) long tails. Males are larger than females.[61]Adult domestic cats typically weigh between 4 and 5kg (9 and 11lb).[44] Skeleton Cats have sevencervical vertebrae(as do mostmammals); 13thoracic vertebrae(humans have 12); sevenlumbar vertebrae(humans have five); threesacral vertebrae(as do most mammals, but humans have five); and a variable number ofcaudal vertebraein the tail (humans have only three to five vestigial caudal vertebrae, fused into an internalcoccyx).[62]: 11 The extra lumbar and thoracic vertebrae account for the cat's spinal mobility and flexibility. Attached to the spine are 13 ribs, the shoulder, and thepelvis.[62]: 16 Unlike human arms, cat forelimbs are attached to the shoulder by free-floatingclaviclebones which allow them to pass their body through any space into which they can fit their head.[63] Skull  Cat skull  A cat with its mouth open exposing its teeth The cat skull is unusual among mammals in having very largeeye socketsand a powerful specialized jaw.[64]: 35 Within the jaw, cats have teeth adapted for killing prey and tearing meat. When it overpowers its prey, a cat delivers a lethal neck bite with its two longcanine teeth, inserting them between two of the prey'svertebraeand severing itsspinal cord, causing irreversibleparalysisand death.[65]Compared to other felines, domestic cats have narrowly spaced canine teeth relative to the size of their jaw, which is an adaptation to their preferred prey of small rodents, which have small vertebrae.[65]Thepremolarand firstmolartogether compose thecarnassialpair on each side of the mouth, which efficiently shears meat into small pieces, like a pair of scissors. These are vital in feeding, since cats' smallmolarscannot chew food effectively, and cats are largely incapable of mastication.[64]: 37 Although cats tend to have better teeth than most humans, with decay generally less likely because of a thicker protective layer of enamel, a less damaging saliva, less retention of food particles between teeth, and a diet mostly devoid of sugar, they are nonetheless subject to occasional tooth loss and infection.[66] Claws  Shed claw sheaths Cats have protractible and retractable claws.[67]In their normal, relaxed position, the claws are sheathed with the skin and fur around the paw's toe pads. This keeps the claws sharp by preventing wear from contact with the ground and allows for the silent stalking of prey. The claws on the forefeet are typically sharper than those on the hindfeet.[68]Cats can voluntarily extend their claws on one or more paws. They may extend their claws in hunting or self-defense, climbing,kneading, or for extra traction on soft surfaces. Cats shed the outside layer of their claw sheaths when scratching rough surfaces.[69] Most cats have five claws on their front paws and four on their rear paws. Thedewclawisproximalto the other claws. More proximally is a protrusion which appears to be a sixth "finger". This special feature of the front paws on the inside of the wrists has no function in normal walking but is thought to be an antiskidding device used while jumping. Some cat breeds are prone to having extra digits ("polydactyly").[70]Polydactylous cats occur along North America's northeast coast and in Great Britain.[71] Ambulation The cat isdigitigrade. It walks on the toes, with the bones of the feet making up the lower part of the visible leg.[72]Unlike most mammals, it uses a "pacing"gaitand moves both legs on one side of the body before the legs on the other side. It registers directly by placing each hind paw close to the track of the corresponding fore paw, minimizing noise and visible tracks. This also provides sure footing for hind paws when navigating rough terrain. As it speeds up from walking to trotting, its gait changes to a "diagonal" gait: The diagonally opposite hind and fore legs move simultaneously.[73] Balance 13:37 Comparison of cat righting reflexes ingravityand zero gravity Most breeds of cat are noted fond of sitting in high places, orperching. A higher place may serve as a concealed site from which to hunt; domestic cats strike prey by pouncing from a perch such as a tree branch. Another possible explanation is that height gives the cat a better observation point, allowing it to survey its territory. A cat falling from heights of up to 3 meters (9.8ft) can right itself and land on its paws.[74] During a fall from a high place, a cat reflexively twists its body and rights itself to land on its feet using its acute sense of balance and flexibility. This reflex is known as thecat righting reflex.[75]A cat always rights itself in the same way during a fall, if it has enough time to do so, which is the case in falls of 90cm (2ft 11in) or more.[76]How cats are able to right themselves when falling has been investigated as the "falling cat problem". Senses Main article:Cat senses Vision  Reflection of camera flash from thetapetum lucidum Cats have excellentnight visionand can see at only one-sixth the light level required for human vision.[64]: 43 This is partly the result of cat eyes having atapetum lucidum, which reflects any light that passes through theretinaback into the eye, thereby increasing the eye's sensitivity to dim light.[77]Large pupils are an adaptation to dim light. The domestic cat hasslit pupils, which allow it to focus bright light withoutchromatic aberration.[78]At low light, a cat's pupils expand to cover most of the exposed surface of its eyes.[79]The domestic cat has rather poorcolor visionand only two types ofcone cells, optimized for sensitivity to blue and yellowish green; its ability to distinguish between red and green is limited.[80]A response to middle wavelengths from a system other than therod cellsmight be due to a third type of cone. This appears to be an adaptation to low light levels rather than representing truetrichromaticvision.[81] Hearing The domestic cat's hearing is most acute in the range of 500Hz to 32kHz.[82]It can detect an extremely broad range of frequencies ranging from 55Hz to 79,000Hz. It can hear a range of 10.5octaves, while humans and dogs can hear ranges of about 9 octaves.[83][84]Its hearing sensitivity is enhanced by its large movable outer ears, thepinnae, which amplify sounds and help detect the location of a noise. It can detectultrasound, which enables it to detect ultrasonic calls made byrodentprey.[85][86]Recent research has shown that cats have socio-spatial cognitive abilities to create mental maps of owners' locations based on hearing owners' voices.[87] Smell Cats have an acute sense of smell, due in part to their well-developedolfactory bulband a large surface ofolfactory mucosa, about5.8 square centimetres (29⁄32square inch) in area, which is about twice that of humans.[88]Cats and many other animals have aJacobson's organin their mouths that is used in the behavioral process offlehmening. It allows them to sense certain aromas in a way that humans cannot. Cats are sensitive topheromonessuch as3-mercapto-3-methylbutan-1-ol,[89]which they use to communicate throughurine sprayingand marking withscent glands.[90]Many cats also respond strongly to plants that containnepetalactone, especiallycatnip, as they can detect that substance at less than one part per billion.[91]About 70–80% of cats are affected by nepetalactone.[92]This response is also produced by other plants, such as silver vine (Actinidia polygama) and the herbvalerian; it may be caused by the smell of these plants mimicking a pheromone and stimulating cats' social or sexual behaviors.[93] Taste Cats have relatively fewtaste budscompared to humans (470 or so versus more than 9,000 on the human tongue).[94]Domestic and wild cats share ataste receptor gene mutationthat keeps their sweet taste buds from binding to sugary molecules, leaving them with no ability to tastesweetness.[95]Their taste buds instead respond toacids,amino acidslike protein, and bitter tastes.[96]Cats also have a distinct temperature preference for their food, preferring food with a temperature around 38°C (100°F) which is similar to that of a fresh kill and routinely rejecting food presented cold or refrigerated (which would signal to the cat that the "prey" item is long dead and therefore possibly toxic or decomposing).[94] Whiskers  The whiskers of a cat are highly sensitive to touch To aid with navigation and sensation, cats have dozens of movablewhiskers (vibrissae)over their body, especially their faces. These provide information on the width of gaps and on the location of objects in the dark, both by touching objects directly and by sensing air currents; they also trigger protectiveblink reflexesto protect the eyes from damage.[64]: 47  Behavior See also:Cat behavior  Cat lying onrice straw Outdoor cats are active both day and night, although they tend to be slightly more active at night.[97]Domestic cats spend the majority of their time in the vicinity of their homes but can range many hundreds of meters from this central point. They establishterritoriesthat vary considerably in size, in one study ranging from 7to 28 hectares (17–69 acres).[98]The timing of cats' activity is quite flexible and varied, which means house cats may be moreactive in the morning and evening, as a response to greater human activity at these times.[99] Cats conserve energy by sleeping more than most animals, especially as they grow older. The daily duration of sleep varies, usually between 12 and 16 hours, with 13 and 14 being the average. Some cats can sleep as much as 20 hours. The term "cat nap" for a short rest refers to the cat's tendency to fall asleep (lightly) for a brief period. While asleep, cats experience short periods ofrapid eye movement sleepoften accompanied by muscle twitches, which suggests they are dreaming.[100] Sociability The social behavior of the domestic cat ranges from widely dispersed individuals toferal cat coloniesthat gather around a food source, based on groups of co-operating females.[101][102]Within such groups, one cat is usually dominant over the others.[103]Each cat in a colony holds a distinct territory, with sexually active males having the largest territories, which are about 10 times larger than those of female cats and may overlap with several females' territories. These territories are marked byurine spraying, by rubbing objects at head height with secretions from facial glands, and bydefecation.[90]Between these territories are neutral areas where cats watch and greet one another without territorial conflicts. Outside these neutral areas, territory holders usually chase away stranger cats, at first by staring, hissing, andgrowlingand, if that does not work, by short but noisy and violent attacks. Despite this colonial organization, cats do not have a social survival strategy or apack mentality, and always hunt alone.[104] Life in proximity to humans and other domestic animals has led to a symbiotic social adaptation in cats, and cats may express great affection toward humans or other animals.Ethologically, a cat's human keeper functions as if a mother surrogate.[105]Adult cats live their lives in a kind of extended kittenhood, a form of behavioralneoteny. Their high-pitched sounds may mimic the cries of a hungry human infant, making them particularly difficult for humans to ignore.[106]Some pet cats are poorly socialized. In particular, older cats show aggressiveness toward newly arrived kittens, which include biting and scratching; this type of behavior is known as feline asocial aggression.[107] Redirected aggressionis a common form of aggression which can occur in multiple cat households. In redirected aggression there is usually something that agitates the cat: this could be a sight, sound, or another source of stimuli which causes a heightened level of anxiety or arousal. If the cat cannot attack the stimuli, it may direct anger elsewhere by attacking or directing aggression to the nearest cat, dog, human or other being.[108][109] Domestic cats'scent rubbingbehavior toward humans or other cats is thought to be a feline means for social bonding.[110] Communication Main article:Cat communication  Vocalizing domestic cat Domestic cats use manyvocalizationsfor communication, includingpurring,trilling, hissing, growling/snarling, grunting, and several different forms of meowing.[7]Theirbody language, including position of ears and tail, relaxation of the whole body, and kneading of the paws, are all indicators of mood. The tail and ears are particularly important social signal mechanisms in cats. A raised tail indicates a friendly greeting, and flattened ears indicates hostility. Tail-raising also indicates the cat's position in the group'ssocial hierarchy, with dominant individuals raising their tails less often than subordinate ones.[111]Feral cats are generally silent.[112]: 208 Nose-to-nose touching is also a common greeting and may be followed bysocial grooming, which is solicited by one of the cats raising and tilting its head.[102] Purringmay have developed as an evolutionary advantage as a signaling mechanism of reassurance between mother cats andnursingkittens, who are thought to use it as a care-soliciting signal.[113]Post-nursing cats also often purr as a sign of contentment: when being petted, becoming relaxed,[114][115]or eating. Even though purring as popularly interpreted as indicative of pleasure, it has been recorded in a wide variety of circumstances, most of which involve physical contact between the cat and another, presumably trusted individual.[113]Some cats have been observed to purr continuously when chronically ill or in apparent pain.[116] The exact mechanism by which cats purr has long been elusive, but it has been proposed that purring is generated via a series of sudden build-ups and releases of pressure as theglottisis opened and closed, which causes thevocal foldsto separate forcefully. The laryngeal muscles in control of the glottis are thought to be driven by aneural oscillatorwhich generates a cycle of contraction and release every 30-40 milliseconds (giving a frequency of 33 to 25 Hz).[113][117][118] Grooming  The hookedpapillaeon a cat's tongue act like ahairbrushto help clean and detangle fur Cats are known for spending considerable amounts of time licking their coats to keep them clean.[119]The cat's tongue has backward-facing spines about 500μmlong, which are calledpapillae. These containkeratinwhich makes them rigid[120]so the papillae act like a hairbrush. Some cats, particularly longhaired cats, occasionally regurgitatehairballsof fur that have collected in their stomachs from grooming. These clumps of fur are usually sausage-shaped and about2–3cm (3⁄4–1+1⁄4in) long. Hairballs can be prevented with remedies that ease elimination of the hair through thegut, as well as regular grooming of the coat with a comb or stiff brush.[119] Fighting  A domestic cat's arched back, raised fur and an open-mouthed hiss are signs of aggression Among domestic cats, males are more likely to fight than females.[121]Among feral cats, the most common reason forcat fightingis competition between two males to mate with a female. In such cases, most fights are won by the heavier male.[122]Another common reason for fighting in domestic cats is the difficulty of establishing territories within a small home.[121]Female cats also fight over territory or to defend their kittens. Neutering will decrease or eliminate this behavior in many cases, suggesting that the behavior is linked tosex hormones.[123] When cats become aggressive, they try to make themselves appear larger and more threatening by raising their fur, arching their backs, turning sideways and hissing or spitting.[124]Often, the ears are pointed down and back to avoid damage to the inner ear and potentially listen for any changes behind them while focused forward. They may also vocalize loudly and bare their teeth in an effort to further intimidate their opponent. Fights usually consist of grappling and delivering powerful slaps to the face and body with the forepaws as well as bites. Cats also throw themselves to the ground in a defensive posture to rake their opponent's belly with their powerful hind legs.[125] Serious damage is rare, as the fights are usually short in duration, with the loser running away with little more than a few scratches to the face and ears. Fights for mating rights are typically more severe and injuries may include deep puncture wounds and lacerations. Normally, serious injuries from fighting are limited to infections of scratches and bites, though these can occasionally kill cats if untreated. In addition, bites are probably the main route of transmission offeline immunodeficiency virus.[126]Sexually active males are usually involved in many fights during their lives, and often have decidedly battered faces with obvious scars and cuts to their ears and nose.[127] Hunting and feeding See also:Cat nutrition  A domestic cat with its prey, adeermouse Cat "playing" with a mouse is interrupted by dog in Estonia, Kõrvemaa (July 2022) The shape and structure of cats' cheeks is insufficient to allow them to take in liquids using suction. Therefore, when drinking they lap with the tongue to draw liquid upward into their mouths. Lapping at a rate of four times a second, the cat touches the smooth tip of its tongue to the surface of the water, and quickly retracts it like a corkscrew, drawing water upward.[128][129] Feral cats and free-fed house cats consume several small meals in a day. The frequency and size of meals varies between individuals. They select food based on its temperature, smell and texture; they dislike chilled foods and respond most strongly to moist foods rich in amino acids, which are similar to meat. Cats reject novel flavors (a response termedneophobia) and learn quickly toavoid foods that have tasted unpleasantin the past.[104][130]It is also a common misconception that cats like milk/cream, as they tend to avoid sweet food and milk. Most adult cats arelactose intolerant; the sugar in milk is not easily digested and may cause soft stools ordiarrhea.[131]Some also develop odd eating habits and like to eat or chew on things like wool, plastic, cables, paper, string, aluminum foil, or even coal. This condition,pica, can threaten their health, depending on the amount and toxicity of the items eaten.[132] Cats hunt small prey, primarily birds and rodents,[133]and are often used as a form of pest control.[134][135]Cats use two hunting strategies, either stalking prey actively, orwaiting in ambushuntil an animal comes close enough to be captured.[136]The strategy used depends on the prey species in the area, with cats waiting in ambush outside burrows, but tending to actively stalk birds.[137]: 153 Domestic cats are a majorpredator of wildlifein the United States, killing an estimated 1.3 to 4.0 billion birds and 6.3 to 22.3 billion mammals annually.[138] Certain species appear more susceptible than others; in one English village, for example, 30% of house sparrow mortality was linked to the domestic cat.[139]In the recovery of ringed robins (Erithacus rubecula) and dunnocks (Prunella modularis) in Britain, 31% of deaths were a result of cat predation.[140]In parts of North America, the presence of larger carnivores such ascoyoteswhich prey on cats and other small predators reduces the effect of predation by cats and other small predators such asopossumsandraccoonson bird numbers and variety.[141] Perhaps the best-known element of cats' hunting behavior, which is commonly misunderstood and often appalls cat owners because it looks like torture, is that cats often appear to "play" with prey by releasing it after capture. Thiscat and mousebehavior is due to an instinctive imperative to ensure that the prey is weak enough to be killed without endangering the cat.[142] Another poorly understood element of cat hunting behavior is the presentation of prey to human guardians. One explanation is that cats adopt humans into their social group and share excess kill with others in the group according to thedominance hierarchy, in which humans are reacted to as if they are at, or near, the top.[143]Another explanation is that they attempt to teach their guardians to hunt or to help their human as if feeding "an elderly cat, or an inept kitten".[144]This hypothesis is inconsistent with the fact that male cats also bring home prey, despite males having negligible involvement in raising kittens.[137]: 153  Play Main article:Cat play and toys Play fight between kittens aged 14 weeks Domestic cats, especially young kittens, are known for their love of play. This behavior mimics hunting and is important in helping kittens learn to stalk, capture, and kill prey.[145]Cats also engage in play fighting, with each other and with humans. This behavior may be a way for cats to practice the skills needed for real combat, and might also reduce any fear they associate with launching attacks on other animals.[146] Cats also tend to play with toys more when they are hungry.[147]Owing to the close similarity between play and hunting, cats prefer to play with objects that resemble prey, such as small furry toys that move rapidly, but rapidly lose interest. They becomehabituatedto a toy they have played with before.[148]String is often used as a toy, but if it is eaten, it can become caught at the base of the cat's tongue and then move into theintestines, a medical emergency which can cause serious illness, even death.[149]Owing to the risks posed by cats eating string, it is sometimes replaced with alaser pointer's dot, which cats may chase.[150] Reproduction  When cats mate, the tomcat (male) bites the scruff of the female's neck as she assumes a position conducive tomatingknown aslordosis behavior. See also:Kitten Female cats, called queens, arepolyestrouswith severalestruscycles during a year, lasting usually 21 days. They are usually ready to mate between early February and August.[151] Several males, called tomcats, are attracted to a female in heat. They fight over her, and the victor wins the right to mate. At first, the female rejects the male, but eventually, the female allows the male to mate. The female utters a loud yowl as the male pulls out of her because a male cat'spenishas a band of about 120–150 backward-pointingpenile spines, which are about1mm (1⁄32in) long; upon withdrawal of the penis, the spines may provide the female with increased sexual stimulation, which acts toinduce ovulation.[152] After mating, the female cleans hervulvathoroughly. If a male attempts to mate with her at this point, the female attacks him. After about 20 to 30 minutes, once the female is finished grooming, the cycle will repeat.[153]Because ovulation is not always triggered by a single mating, females may not be impregnated by the first male with which they mate.[154]Furthermore, cats aresuperfecund; that is, a female may mate with more than one male when she is in heat, with the result that different kittens in a litter may have different fathers.[153] Themorulaforms 124 hours after conception. At 148 hours, earlyblastocystsform. At 10–12 days, implantation occurs.[155]Thegestationof queens lasts between 64 and 67 days, with an average of 65 days.[151][156]  Radiography of a pregnant cat. The skeletons of two fetuses are visible on the left and right of the uterus.  A newborn kitten Data on the reproductive capacity of more than 2,300 free-ranging queens were collected during a study between May 1998 and October 2000. They had one to six kittens perlitter, with an average of three kittens. They produced a mean of 1.4 litters per year, but a maximum of three litters in a year. Of 169 kittens, 127 died before they were six months old due to a trauma caused in most cases by dog attacks and road accidents.[9]The first litter is usually smaller than subsequent litters. Kittens are weaned between six and seven weeks of age. Queens normally reach sexual maturity at 5–10 months, and males at 5–7 months. This varies depending on breed.[153]Kittens reachpubertyat the age of 9–10 months.[151] Cats are ready to go to new homes at about 12 weeks of age, when they are ready to leave their mother.[157]They can be surgicallysterilized(spayed orcastrated) as early as seven weeks to limit unwanted reproduction.[158]This surgery also prevents undesirable sex-related behavior, such as aggression,territory marking(spraying urine) in males and yowling (calling) in females. Traditionally, this surgery was performed at around six to nine months of age, but it is increasingly being performed beforepuberty, at about three to six months.[159]In the United States, about 80% of household cats are neutered.[160] Lifespan and health Main articles:Cat healthandAging in cats The average lifespan of pet cats has risen in recent decades. In the early 1980s, it was about seven years,[161]: 33 [162]rising to 9.4 years in 1995[161]: 33 and about 15 years in 2021. Some cats have been reported as surviving into their 30s,[163]with the oldest known cat,Creme Puff, dying at a verified age of 38.[164] Neutering increases life expectancy: one study found castrated male cats live twice as long as intact males, while spayed female cats live 62% longer than intact females.[161]: 35 Having a catneuteredconfers health benefits, because castrated males cannot developtesticular cancer, spayed females cannot developuterineorovarian cancer, and both have a reduced risk ofmammary cancer.[165] Disease Main article:Feline diseases About 250 heritablegenetic disordershave been identified in cats, many similar to humaninborn errors of metabolism.[166]The high level of similarity among themetabolismof mammals allows many of these feline diseases to be diagnosed usinggenetic teststhat were originally developed for use in humans, as well as the use of cats asanimal modelsin the study of the human diseases.[167][168]Diseases affecting domestic cats include acute infections,parasitic infestations, injuries, and chronic diseases such askidney disease,thyroid disease, andarthritis.Vaccinationsare available for many infectious diseases, as are treatments to eliminate parasites such as worms, ticks, and fleas.[169] Ecology Habitats  Atabby catin snowy weather The domestic cat is acosmopolitan speciesand occurs across much of the world.[59]It is adaptable and now present on all continents exceptAntarctica, and on 118 of the 131 main groups of islands, even on the isolatedKerguelen Islands.[170][171]Due to its ability to thrive in almost any terrestrial habitat, it is among the world's mostinvasive species.[172]It lives on small islands with no human inhabitants.[173]Feral cats can live in forests, grasslands, tundra, coastal areas, agricultural land, scrublands, urban areas, and wetlands.[174] The unwantedness that leads to the domestic cat being treated as an invasive species is twofold. On one hand, as it is little altered from the wildcat, it can readily interbreed with the wildcat. Thishybridizationposes a danger to the genetic distinctiveness of some wildcat populations, particularly inScotlandandHungary, possibly also theIberian Peninsula, and where protected natural areas are in close proximity to human-dominated landscapes, such asKruger National ParkinSouth Africa.[175][56]On the other hand, and perhaps more obviously, its introduction to places where no native felines are present contributes to the decline of native species.[176] Ferality Main article:Feral cat  Feralfarm cat Feral cats are domestic cats that were born in or have reverted to a wild state. They are unfamiliar with and wary of humans and roam freely in urban and rural areas.[10]The numbers of feral cats is not known, but estimates of the United States feral population range from 25 to 60 million.[10]Feral cats may live alone, but most are found in largecolonies, which occupy a specific territory and are usually associated with a source of food.[177]Famous feral cat colonies are found in Rome around theColosseumandForum Romanum, with cats at some of these sites being fed and given medical attention by volunteers.[178] Public attitudes toward feral cats vary widely, from seeing them as free-ranging pets to regarding them as vermin.[179] Some feral cats can be successfully socialized and 're-tamed' for adoption; young cats, especially kittens[180]and cats that have had prior experience and contact with humans are the most receptive to these efforts. Impact on wildlife Main article:Cat predation on wildlife On islands, birds can contribute as much as 60% of a cat's diet.[181]In nearly all cases, the cat cannot be identified as the sole cause for reducing the numbers of island birds, and in some instances, eradication of cats has caused a "mesopredator release" effect;[182]where the suppression of top carnivores creates an abundance of smaller predators that cause a severe decline in their shared prey. Domestic cats are a contributing factor to the decline of many species, a factor that has ultimately led, in some cases, to extinction.The South Island piopio,Chatham rail,[140]and theNew Zealand merganser[183]are a few from a long list, with the most extreme case being the flightlessLyall's wren, which was driven to extinction only a few years after its discovery.[184][185]One feral cat in New Zealand killed 102New Zealand lesser short-tailed batsin seven days.[186]In the US, feral and free-ranging domestic cats kill an estimated 6.3 – 22.3 billion mammals annually.[138] In Australia, the impact of cats on mammal populations is even greater than the impact of habitat loss.[187]More than one million reptiles are killed by feral cats each day, representing 258 species.[188]Cats have contributed to the extinction of theNavassa curly-tailed lizardandChioninia coctei.[176] Interaction with humans Main article:Human interaction with cats  A cat sleeping on a man's lap Cats are commonpetsthroughout the world, and their worldwide population as of 2007 exceeded 500million.[189]Cats have been used for millennia to control rodents, notablyaround grain storesandaboard ships, and both uses extend to the present day.[190][191] As well as being kept as pets, cats are also used in the internationalfur trade[192]and leather industries for making coats, hats, blankets, and stuffed toys;[193]and shoes, gloves, and musical instruments respectively[194](about 24 cats are needed to make a cat-fur coat).[195]This use has been outlawed in the United States since 2000 and in the European Union (as well as the United Kingdom) since 2007.[196] Cat pelts have been used for superstitious purposes as part of the practice ofwitchcraft,[197]and are still made into blankets inSwitzerlandastraditional medicinethought to curerheumatism.[198] A few attempts to build a cat census have been made over the years, both through associations or national and international organizations (such as that of theCanadian Federation of Humane Societies[199]) and over the Internet,[200][201]but such a task does not seem simple to achieve. General estimates for the global population of domestic cats range widely from anywhere between 200 million to 600 million.[202][203][204][205][206]Walter Chandohamade his career photographing cats after his 1949 images ofLoco, an especially charming stray taken in, were published around the world. He is reported to have photographed 90,000 cats during his career and maintained an archive of 225,000 images that he drew from for publications during his lifetime.[207] Shows Main article:Cat show Acat showis a judged event in which the owners of cats compete to win titles in various cat-registering organizations by entering their cats to be judged after a breed standard.[208]It is often required that a cat must be healthy and vaccinated in order to participate in a cat show.[208]Bothpedigreedand non-purebredcompanion ("moggy") cats are admissible, although the rules differ depending on the organization. Competing cats are compared to the applicable breed standard, and assessed for temperament.[208] Infection Main article:Feline zoonosis Cats can be infected or infested withviruses,bacteria,fungus,protozoans,arthropodsor worms that can transmit diseases to humans.[209]In some cases, the cat exhibits nosymptomsof the disease.[210]The same disease can then become evident in a human. The likelihood that a person will become diseased depends on the age andimmunestatus of the person. Humans who have cats living in their home or in close association are more likely to become infected. Others might also acquire infections from catfecesandparasitesexiting the cat's body.[209][211]Some of the infections of most concern includesalmonella,cat-scratch diseaseandtoxoplasmosis.[210] History and mythology Main articles:Cultural depictions of catsandCats in ancient Egypt Inancient Egypt, cats wereworshipped, and the goddessBastetoften depicted in cat form, sometimes taking on the war-like aspect of a lioness. The Greek historianHerodotusreported that killing a cat was forbidden, and when a household cat died, the entire family mourned and shaved their eyebrows. Families took their dead cats to the sacred city ofBubastis, where they were embalmed and buried in sacred repositories. Herodotus expressed astonishment at the domestic cats in Egypt, because he had only ever seen wildcats.[212] Ancient Greeks and Romans keptweaselsas pets, which were seen as the ideal rodent-killers. The earliest unmistakable evidence of the Greeks having domestic cats comes from two coins fromMagna Graeciadating to the mid-fifth century BC showing Iokastos and Phalanthos, the legendary founders ofRhegionandTarasrespectively, playing with their pet cats. The usual ancient Greek word for 'cat' wasailouros, meaning 'thing with the waving tail'. Cats are rarely mentioned inancient Greek literature.Aristotleremarked in hisHistory of Animalsthat "female cats are naturallylecherous." The Greeks latersyncretizedtheir own goddessArtemiswith the Egyptian goddess Bastet, adopting Bastet's associations with cats and ascribing them to Artemis. InOvid'sMetamorphoses, when the deities flee to Egypt and take animal forms, the goddessDianaturns into a cat.[213][214] Cats eventually displacedweaselsas the pest control of choice because they were more pleasant to have around the house and were more enthusiastic hunters of mice. During theMiddle Ages, many of Artemis's associations with cats were grafted onto theVirgin Mary. Cats are often shown in icons ofAnnunciationand of theHoly Familyand, according toItalian folklore, on the same night that Mary gave birth toJesus, a cat inBethlehemgave birth to a kitten.[215]Domestic cats were spread throughout much of the rest of the world during theAge of Discovery, asships' catswere carried onsailing shipsto control shipboard rodents and as good-luck charms.[50] Several ancient religions believed cats are exalted souls, companions or guides for humans, that are all-knowing but mute so they cannot influence decisions made by humans. In Japan, themaneki nekocat is a symbol of good fortune.[216]InNorse mythology,Freyja, the goddess of love, beauty, and fertility, is depicted as riding a chariot drawn by cats.[217]InJewish legend, the first cat was living in the house of the first manAdamas a pet that got rid ofmice. The cat was once partnering with the first dog before the latter broke an oath they had made which resulted in enmity between the descendants of these two animals. It is also written that neither cats norfoxesare represented in the water, while every other animal has an incarnation species in the water.[218]Although no species are sacred in Islam,cats are revered by Muslims. Some Western writers have statedMuhammadhad a favorite cat,Muezza.[219]He is reported to have loved cats so much, "he would do without his cloak rather than disturb one that was sleeping on it".[220]The story has no origin in early Muslim writers, and seems to confuse a story of a laterSufisaint,Ahmed ar-Rifa'i, centuries after Muhammad.[221]One of the companions of Muhammad was known asAbu Hurayrah("father of the kitten"), in reference to his documented affection to cats.[222]  The ancient Egyptiansmummifieddead cats out of respect in the same way that they mummified people[4]  AncientRoman mosaicof a cat killing apartridgefrom theHouse of the FauninPompeii  A 19th-century drawing of a tabby cat Superstitions and rituals  Some cultures are superstitious about black cats, ascribing either good or bad luck to them Many cultures have negativesuperstitionsabout cats. An example would be the belief that encountering ablack cat("crossing one's path") leads to bad luck, or that cats are witches'familiarsused to augment a witch's powers and skills. The killing of cats in MedievalYpres,Belgium, is commemorated in the innocuous present-dayKattenstoet(cat parade).[223]In mid-16th century France,cats would be burnt aliveas a form of entertainment. According toNorman Davies, the assembled people "shrieked with laughter as the animals, howling with pain, were singed, roasted, and finallycarbonized".[224] James Frazerwrote that "It was the custom to burn a basket, barrel, or sack full of live cats, which was hung from a tall mast in the midst of the bonfire; sometimes afoxwas burned. The people collected the embers and ashes of the fire and took them home, believing that they brought good luck. The French kings often witnessed these spectacles and even lit the bonfire with their own hands. In 1648Louis XIV, crowned with a wreath of roses and carrying a bunch of roses in his hand, kindled the fire, danced at it and partook of the banquet afterwards in the town hall. But this was the last occasion when a monarch presided at the midsummer bonfire in Paris. AtMetzmidsummer fires were lighted with great pomp on the esplanade, and a dozen cats, enclosed inwickercages, were burned alive in them, to the amusement of the people. Similarly, atGap, in thedepartmentof theHautes-Alpes, cats used to be roasted over the midsummer bonfire."[225] According to a myth in many cultures, cats have multiple lives. In many countries, they are believed to have nine lives, but in Italy, Germany, Greece, Brazil and some Spanish-speaking regions, they are said to have seven lives,[226][227]while in Arabic traditions, the number of lives is six.[228]The myth is attributed to the natural suppleness and swiftness cats exhibit to escape life-threatening situations.[citation needed]Also lending credence to this myth is the fact that falling cats often land on their feet, using an instinctiverighting reflexto twist their bodies around. Nonetheless, cats can still be injured or killed by a high fall.[229]

Very sweet and cute bird.

Thetamarinsaresquirrel-sizedNew World monkeysfrom thefamilyCallitrichidaein thegenusSaguinus. They are the first offshoot in the Callitrichidae tree, and therefore are the sister group of acladeformed by thelion tamarins,Goeldi's monkeysandmarmosets.[3] Tamarins[1][2]Emperor tamarin(Saguinus imperator)Scientific classificationKingdom:AnimaliaPhylum:ChordataClass:MammaliaOrder:PrimatesSuborder:HaplorhiniInfraorder:SimiiformesFamily:CallitrichidaeGenus:Saguinus Hoffmannsegg, 1807Type speciesSaguinus ursulus Hoffmannsegg, 1807 Species 22 species, seetext Synonyms HapanellaGray, 1870 MarikinaLesson, 1840 MidasE. Geoffroy, 1812 MystaxGray, 1870 OedipomidusReichenbach, 1862 OedipusLesson, 1840 SeniocebusGray, 1870 TamarinGray, 1870 Contents Taxonomy and evolutionary historyEdit Hershkovitz (1977) recognised ten species in the genusSaguinus, further divided into 33 morphotypes based on facial pelage.[4]A later classification into two clades was based on variations in dental measurements.[5]A taxonomic review (Rylands et al., 2016) showed the tamarins are a sister group to all other callitrichids, branching off 15–13 million years ago. Within this clade, six species groups are historically recognised,nigricollis,mystax,midas,inustus,bicolorandoedipus, five of which were shown to be valid withSanguinus inustusplaced within themidasgroup. The review noted that the smaller-bodiednigricollisgroup began diverging 11–8 million years ago, leading the authors to move them to a separate genus,Leontocebus(saddle-back tamarins).[6][7]While a 2018 study proposed thatLeontocebusdoes not have sufficient enough divergence fromSaguinusto be in its own genus, and thus should be reclassified it as asubgenusofSaguinus, this proposal has since found significant traction.[8]The same study found themystaxgroup of tamarins to be distinct enough to be classified in the subgenusTamarinus.[3]As of 2021 this proposal has not been universally accepted by primatologists.[9] Taxonomic classificationEdit Following the taxonomic review of tamarins by Rylands et al. (2016) and Garbino & Martins-Junior (2018), there are 22 species in the genusSaguinuswith 19 subspecies.[6][3][10] GenusSaguinus SubgenusSaguinusHoffmannsegg, 1807 S. midasgroup Golden-handed tamarin, midas tamarin, or red-handed tamarin,Saguinus midas Western black-handed tamarin orblack tamarin,Saguinus niger Eastern black-handed tamarin,Saguinus ursulus[11] S. bicolorgroup Pied tamarin,Saguinus bicolor Martins's tamarin,Saguinus martinsi Martins's bare-face tamarin,Saguinus martinsi martinsi Ochraceus bare-face tamarin,Saguinus martinsi ochraceus S. oedipusgroup Cotton-top tamarinor Pinché tamarin,Saguinus oedipus Geoffroy's tamarin,Saguinus geoffroyi White-footed tamarin,Saguinus leucopus SubgenusTamarinusTrouessart, 1904 Moustached tamarin,Saguinus mystax Spix's moustached tamarin,Saguinus mystax mystax Red-capped tamarin,Saguinus mystax pileatus White-rump moustached tamarin,Saguinus mystax pluto White-lipped tamarin,Saguinus labiatus Geoffroy's red-bellied tamarin,Saguinus labiatus labiatus Thomas's red-bellied tamarin,Saguinus labiatus labiatus Gray's red-bellied tamarin,Saguinus labiatus labiatus Emperor tamarin,Saguinus imperator Black-chinned emperor tamarin,Saguinus imperator imperator Bearded emperor tamarin,Saguinus imperator subgrisescens Mottle-faced tamarin,Saguinus inustus DescriptionEdit Tamarin species vary considerably in appearance, ranging from nearly all black through mixtures of black, brown and white.Mustache-like facial hairs are typical for many species. Their body size ranges from 13 to 30cm (5.1 to 11.8in) (plus a 25-to-44cm-long (9.8-to-17.3in)tail). They weigh from 348 to 575 grams (12.3 to 20.3oz).[12]Incaptivity,red-bellied tamarinshave been recorded living up to 20.5 years,[13]whilecotton-top tamarinscan live up to 23 years old.[14] DistributionEdit Tamarins range from southernCentral Americathrough centralSouth America, where they are found in northwesternColombia, theAmazon basin, andthe Guianas.[4] Behavior and reproductionEditLearn more This sectiondoes notciteanysources.(August 2017) Tamarins are inhabitants oftropical rainforestsand open forest areas. They arediurnalandarboreal, and run and jump quickly through the trees. Tamarins live together in groups of up to 40 members consisting of one or more families. More frequently, though, groups are composed of just three to nine members. Tamarins areomnivores, eating fruits and other plant parts as well asspiders,insects, small vertebrates andbird eggs. Gestationis typically 140 days, andbirthsare normallytwins. The adult males, subadults, and juveniles in the group assist with caring for the young, bringing them to their mother to nurse. After approximately one month the young begin to eat solid food, although they aren't fullyweanedfor another two to three months. They reach full maturity in their second year. Tamarins are almost exclusivelypolyandrous. Cottontop tamarins (Saguinus oedipus) breed cooperatively in the wild. Cronin, Kurian, and Snowdon tested eight cottontop tamarins in a series ofcooperative pulling experiments. Two monkeys were put on opposite sides of a transparent apparatus containing food. Only if both monkeys pulled a handle on their side of the apparatus towards themselves at the same time would food drop down for them to obtain. The results showed that tamarins pulled the handles at a lower rate when alone with the apparatus than when in the presence of a partner. Cronin, Kurian, and Snowdon concluded from this that cottontop tamarins have a good understanding of cooperation. They suggest that cottontop tamarins have developed cooperative behaviour as a cognitive adaptation.[15] In some locations, saddle-back tamarins (subgenusLeontocebus) livesympatricallywith tamarins of the subgenusSanguinus, but the saddle-back tamarins typically occupy lower strata of the forest than do theSanguinusspecies.[16]Saddle-back tamarins have longer and narrower hands thanSanguinusspecies, possibly adaption to differing foraging behavior, as saddle-back tamarins are more likely to search for insects that are hidden in knotholes, crevices,bromeliadtanks and leaf litter, whileSanguinusspecies are more likely to forage for insects that are exposed on surfaces such as leaves or branches.[16]This differentiation in lifestyles was why both were formerly considered different genera.[6] PredatorsEdit While tamarins spend much of their day foraging, they must be on high alert for aerial and terrestrial predators. Due to their small size compared to other primates, they are an easy target for predatory birds, snakes, and mammals.[17] ReferencesEdit ^Groves, C. P.(2005).Wilson, D. E.; Reeder, D. M. (eds.).Mammal Species of the World: A Taxonomic and Geographic Reference(3rded.). Baltimore: Johns Hopkins University Press. pp.133–136.ISBN0-801-88221-4.OCLC62265494. ^Rylands, Anthony B.; Mittermeier, Russell A. (2009). "The Diversity of the New World Primates (Platyrrhini): An Annotated Taxonomy". In Garber, PA; Estrada, A; Bicca-Marques, JC; Heymann, EW;Strier, KB(eds.).South American Primates: Comparative Perspectives in the Study of Behavior, Ecology, and Conservation. Springer. pp.21–54.ISBN978-0-387-78704-6. ^abcGarbino, Guilherme S.T.; Martins-Junior, Antonio M.G. (2018)."Phenotypic evolution in marmoset and tamarin monkeys (Cebidae, Callitrichinae) and a revised genus-level classification".Molecular Phylogenetics and Evolution.118: 156–171.doi:10.1016/j.ympev.2017.10.002.PMID28989098. ^abHershkovitz, Philip (1977).Living New World Monkeys (Platyrrhini): With an Introduction to Primates(1sted.). University of Chicago Press.ISBN9780226327884. ^Natori, M.; Hanihara, T. (1992). "Variations in dental measurements betweenSaguinusspecies and their systematic relationships".Folia Primatologica.58(2): 84–92.doi:10.1159/000156612.PMID1612537. ^abcRylands, Anthony B.; Eckhard W. Heymann; Jessica Lynch Alfaro; Janet C. Buckner; Christian Roos; Christian Matauschek; Jean P. Boubli; Ricardo Sampaio; and Russell A. Mittermeier (2016)."Taxonomic Review of the New World Tamarins (Primates: Callitrichidae)"(PDF).Zoological Journal of the Linnean Society.177(4): 1003–1028.doi:10.1111/zoj.12386. Retrieved19 April2020. ^"Leontocebus".Integrated Taxonomic Information System. Retrieved19 April2020. ^"Leontocebus". ITIS. Retrieved12 November2021. ^"Tamarinus". ITIS. Retrieved2021-11-12. ^Database, Mammal Diversity (6 November 2021),Mammal Diversity Database, Zenodo, retrieved11 November2021 ^Gregorin, R.; De Vivo, M. (2013). "Revalidation ofSaguinus ursulaHoffmannsegg (Primates: Cebidae: Callitrichinae)".Zootaxa.3721(2): 172–182.doi:10.11646/zootaxa.3721.2.4. ^Smith, Richard J.; Jungers, William L. (1997). "Body mass in comparative primatology".Journal of Human Evolution.32(6): 523–559.doi:10.1006/jhev.1996.0122.PMID9210017. ^Weigl, Richard (2005).Longevity of mammals in captivity; from the Living Collections of the world. Vol.48. Kleine Senckenberg-Reihe.ISBN978-3-510-61379-3. ^Hakeem, A.; Sandoval, R.; Jones, M.; Allman, J. (1996). "Brain and life span in primates". In Birren, J. (ed.).Handbook of the Psychology of Aging. Academic Press. pp.78–104. ^Cronin, Katherine A.; Kurian, Aimee V.; Snowdon, Charles T. (2005)."Cooperative problem solving in a cooperatively breeding primate (Saguinus oedipus)".Animal Behaviour.69(1): 133–142.doi:10.1016/j.anbehav.2004.02.024.PMC1483064.PMID16804561. ^abRylands, Anthony B.; Eckhard W. Heymann; Jessica Lynch Alfaro; Janet C. Buckner; Christian Roos; Christian Matauschek; Jean P. Boubli; Ricardo Sampaio; and Russell A. Mittermeier (2016)."Taxonomic Review of the New World Tamarins (Primates: Callitrichidae)"(PDF).Zoological Journal of the Linnean Society.177(4): 1003–1028.doi:10.1111/zoj.12386. Retrieved19 April2020. ^Miller, Lynne (2002).Eat or be Eaten. Cambridge University Press.ISBN978-0-521-01104-4.

Themarmosets(/ˈmɑːrməˌzɛts,-ˌsɛts/),[3][4]also known aszarisorsagoin, are 22New World monkeyspecies of thegeneraCallithrix,Cebuella,Callibella, andMico. All four genera are part of the biologicalfamilyCallitrichidae. The term "marmoset" is also used in reference toGoeldi's marmoset,Callimico goeldii, which is closely related. Marmosets[1][2]Common marmoset(Callithrix jacchus) atTibau do Sul,Rio Grande do NorteScientific classificationKingdom:AnimaliaPhylum:ChordataClass:MammaliaOrder:PrimatesSuborder:HaplorhiniInfraorder:SimiiformesParvorder:PlatyrrhiniFamily:CallitrichidaeGroups included CallibellaM.G.M. van Roosmalen&T. van Roosmalen, 2003(Roosmalens' dwarf marmoset) CallimicoMiranda-Ribeiro, 1922(Goeldi's marmoset) CallithrixErxleben, 1777(Atlantic marmosets) CebuellaGray, 1866(pygmy marmosets) MicoLesson, 1840(Amazonian marmosets) Cladisticallyincluded but traditionally excluded taxa LeontopithecusLesson, 1840(lion tamarins) SaguinusHoffmannsegg, 1807(tamarins) Most marmosets are about 20cm (8in) long. Relative to othermonkeys, they show some apparently primitive features; they haveclawsrather thannails, and tactile hairs on their wrists. They lackwisdom teeth, and theirbrainlayout seems to be relatively primitive. Their body temperature is unusually variable, changing by up to 4°C (7°F) in a day.[5]Marmosets are native to South America and have been found inBolivia,Brazil,Colombia,Ecuador,Paraguay, andPeru.[6]They have also been occasionally spotted in Central America and southern Mexico.[7]They are sometimes kept as pets, though they have specific dietary and habitat needs that require consideration.[8] According to recent research, marmosets exhibitgermline chimerism, which is not known to occur in nature in anyprimatesother thancallitrichids.[9]95% of marmosetfraternal twinstrade blood throughchorionicfusions, making themhematopoieticchimeras.[10][11] Contents EtymologyEdit Callithrixcomes fromAncient Greekand means "beautiful fur". Species listEdit GenusCallithrix—Atlantic marmosets Common marmoset,Callithrix jacchus Black-tufted marmoset,Callithrix penicillata Wied's marmoset,Callithrix kuhlii White-headed marmoset,Callithrix geoffroyi Buffy-headed marmoset,Callithrix flaviceps Buffy-tufted marmoset,Callithrix aurita GenusMico—Amazonian marmosets Rio Acari marmoset,Mico acariensis Silvery marmoset,Mico argentatus White marmoset,Mico leucippe Emilia's marmoset,Mico emiliae Black-headed marmoset,Mico nigriceps Marca's marmoset,Mico marcai Black-tailed marmoset,Mico melanura Santarem marmoset,Mico humeralifer Maués marmoset,Mico mauesi Munduruku marmoset,Mico munduruku Gold-and-white marmoset,Mico chrysoleucos Hershkovitz's marmoset,Mico intermedius Satéré marmoset,Mico saterei Rondon's marmoset,Mico rondoni GenusCallibella—Roosmalens' dwarf marmoset Roosmalens' dwarf marmoset,Callibella humilis GenusCebuella—Pygmy Marmoset Pygmy marmoset,Cebuella pygmaea BehaviorEdit Marmosets are highly active, living in the upper canopy of forest trees, and feeding oninsects,fruit, leaves, tack, sap, and gum. They have long lowerincisors, which allow them to chew holes in tree trunks and branches to harvest the gum inside; some species are specialised feeders on gum.[citation needed] Marmosets live in family groups of three to 15, consisting of one or two breeding females, an unrelated male, their offspring, and occasionally extended family members and unrelated individuals. Their mating systems are highly variable and can includemonogamy,polygyny, andpolyandry. In most species, fraternal twins are usually born, but triplets are not unknown. Like other callitrichines, marmosets are characterized by a high degree of cooperative care of the young and some food sharing and tolerated theft. Adult males, females other than the mother, and older offspring participate in carrying infants. Father marmosets are an exceptionally attentive example of fathers within the animal kingdom, going as far as assisting their mates in giving birth, cleaning up afterbirth, and even biting the umbilical cords attaching their newborn offspring to their mothers. Most groups scent mark and defend the edges of their ranges, but if they are truly territorial is unclear, as group home ranges greatly overlap. The favorite food of marmosets is carbohydrate-rich tree sap, which they reach by gnawing holes in trunks. Their territories are centered on the trees that they regularly exploit in this way. The smaller marmosets venture into the very top of forest canopies to hunt insects that are abundant there.[7] ReferencesEdit ^Groves, C. P.(2005).Wilson, D. E.; Reeder, D. M. (eds.).Mammal Species of the World: A Taxonomic and Geographic Reference(3rded.). 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