Over twenty thousand species of fish live in the seas, the rivers, lakes and oceans. They can look absolutely differently – externally huge shark and tiny smelts are not too similar at each other, however their building and a way of life are almost identical.
Instruction
1. Fishes are animals who chose the water environment for dwelling. Being in water billions of years, during evolution they developed a set of the devices allowing them to survive in this environment that considerably distinguishes them from overland representatives of fauna.
2. The shape of a body of fishes differs in a variety. Types which should float in the prompt rivers have the streamline torpedo-shaped shape, overcoming a current (for example, a trout). And here the animals living in still waters, on the contrary, chose a wide body. It allows them to avoid the predators preferring more compact production. Vida, living at the bottom of reservoirs, have a flat body. It helps them to move on soil.
3. The body of the majority of fishes is covered with the scales emitting slime that allows them to maneuver better in the thickness of water. At the movement the fish uses a tail as a wheel, and side fins help it to keep balance. Fishes have a special body – the swimming bubble filled with air. Thanks to it these animals do not sink.
4. Fishes, as well as overland animals, breathe oxygen, here they only receive it from water. Therefore the respiratory system at them differs. Fishes swallow water which comes after that to gills. Gills are surrounded with network of blood vessels. In this place the oxygen which is contained in water comes to blood, and then is transferred to all fabrics and bodies.
5. Both herbivorous, and predatory types occur among fishes. Some filter plankton from water, others rummage in silt, trying to discover fossils, the third eat seaweed. Predators depending on the sizes can prefer in food different types both insects or small Crustacea, and other fishes and even mammals. In the nature also omnivorous fishes meet.
6. Fishes differ on males and females, and two individuals of a different floor participate in reproduction. The hermaphroditism is widespread among some types – their representatives during life can act in a role and a female, and men's individual.