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