Features of the internal structure of fish in connection with living in the aquatic environment.

Fish are chordates. They, like all vertebrates, have gill lobes. They persist throughout the life of the fish, since gas exchange occurs with their help. Fish have fins. They also have a special sense organ – the lateral line. With its help, fish determine the pressure and flow of water. Fish have a streamlined body, this provides the least resistance during swimming. Bony fish have an intestinal outgrowth called a swim bladder. It helps the fish to emerge and sink to the bottom.