FISH

Fishes have the same general structural components as other vertebrates: a skull, spinal column, limbs, and a tail. Fish limbs have developed into fins, which are adapted for swimming and for providing stability while swimming.

Fishes make up more than half the total number of known vertebrates. There are about 22,000 living species, compared with 21,500 amphibians, reptiles, birds, and mammals. New species of fishes continue to be discovered. It is expected that the eventual number of fish species will approach 28,000.