Fishes (singular: Fish) are a paraphyletic group of aquatic vertebrates, with approximately 25,000 species. It should be noted that there isn't a single specific class for fish. There are actually three: jawless, bony, and cartilaginous fish. Fishes are characterised by a lack of limbs and the presence of fins and scales (in most cases) in their place.

The term fishes is generally used to describe multiple separate species or a school of fish, while fish is used to describe a shoal of a single species.


Nearly every species of fish has gills, with a small number also possessing lungs or a similarly functioning organ. Most fishes evolved them very early on in evolution.


Fishes have a variety of feeding habits, with the groups following all three of the three main feeding behaviours of carnivory, herbivory and omnivory. A large number swallow food whole or shake it around to break it into smaller chunks; sharks and rays are the main exception, as they have sharp teeth capable of tearing flesh.


Most fish fertilise externally and lay eggs, the main exception being cartilaginous fish, of which many species which give birth to live young.