In rivers, lakes, seas and oceans are home to more than 20 thousand different species of fish. Fish that live in fresh water, are called freshwater, and those who live in the salty sea. Like other animals, fish live in warm water, and in cold polar seas.
Most fish can't breathe the air, as the gills can only absorb oxygen dissolved in water. To date, however, survived 3 species of fish have lungs, allowing them to breathe air. For example, living in Africa protopterus may for a short time to get out on the land.
Fish moving in the water, reducing and relaxing the muscles. It also pushes the water, wagging her tail from side to side. And the fins need the fish to change direction and to keep the balance.