What are fish?

Fishes in general are vertebrate animals that live in water and ‘breathe’ by means of gills. They use fins to move in the water and to maintain position and balance. The body of most fish is covered with scales. Fish include three major categories, the classes: Osteichtheys, Chondrichthyes, and Myxiniformes. There are about 32 100 named species of fish, accounting for about half of all the vertebrates. However, not all animals that live in water are fish. Whales and dolphins live in the ocean and breathe by means of lungs.