Fishes in group

To ask ‘what is a fish’ is not an easily answered question as the fish group is such a diverse one. Most fish are scaled, aquatic vertebrates which means they have a skeleton which includes a cranium or skull and a functional backbone. Some species of fish are not vertebrates such as the primitive-looking Hagfish which have a simple cartilaginous skull and a row of springy connective tissues instead of a backbone.

All fish live and survive in water whether it be sea water or freshwater. However, there are a few exceptions such as the Common Eels and Mudskippers who are able to move about on land. Some species of fish such as the Flying Fish, take to the air and are able to glide over 200 metres, skimming the waves like fast flying sea birds. There are other species of fish that remain encased in mud for many months or even years such as the Lungfish.