The most primitive group of vertebrates are fish. They are also the most numerous. All fish live in water.
CHARACTERISTICS OF FISH
- The body of a fish is elongated and pointed at the ends. It is very well adapted to living in water. Fish have fins to help them move. The tail fin acts like a rudder and moves the fish forward. The other fins (pectoral, pelvic, anal and dorsal) help maintain the fish's balance and control its direction.
- The skin of fish is slippery. Thin, bony scales protect their bodies. The scales overlap each other, like slates on a roof.
- Fish breathe using organs called gills. The gills are thin red filaments at the back of the mouth. They are protected by flaps called gill covers (or operculum). Fish breathe by absorbing oxygen dissolved in the water through their gills.
- Fish reproduce by laying small eggs in the water. The eggs do not have a hard outer shell. Baby fish, called fry, hatch from the eggs. Femals lay lots of eggs but only a few live to be adults.
- 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.
PARTS OF A FISH