1.5 Fish

The most primitive group of vertebrates are fish. They are also the most numerous. They live in water

The body of a fish is elongated and pointed at the ends. It is a very well adapted to living in water. 

Fish have fins to help them move and maintain balance.

The skin of fish is slippery. Thin, bony scales protect their bodies.

Fish breathe using organs called gills. They breathe by absorbing oxygen dissolved in the water through their gills.

Fish reproduce by laying small eggs in the water. Baby fish, called fry, hatch from the eggs.

Fish have a special sensory organ on the side of their bodies that other vertebrates do not have. This sensory organ is called the lateral line and allows the fish to detect movements in the water.