Fish at Peoria Zoo
There are more than 24,000 species of fish living today. This class of animals contains three main groups are: the jawless fish, including lamprey and hagfish; the cartilaginous fish (with a skeleton made of cartilage rather than bone), including sharks and rays; and the largest grouping -- the bony fish, including sturgeon, perch, and thousands of others. All fish also have fins, which help them swim forward, turn, and stop, as well as keep upright. Fins come in various shapes and sizes. There are some things that all fish have in common: they breathe with gills. As water flows past the gills, oxygen in the water passes through the gill membranes and into the fish's blood.