More than twenty thousand species of fish live in the seas, rivers, lakes and oceans. They can look completely different - outwardly, a giant shark and a tiny smelt are not very similar to each other, but their structure and lifestyle are almost identical.
Instructions
Step 1
Fish are animals that have chosen an aquatic habitat. Being in water for billions of years, in the course of evolution, they have developed many adaptations that allow them to survive in this environment, which significantly distinguishes them from land representatives of the fauna.
Step 2
The body shape of fish is diverse. A streamlined torpedo-like shape has species that have to swim in rapid rivers, overcoming the current (for example, trout). But animals living in calm waters, on the contrary, chose a wide body. This allows them to avoid predators who prefer more compact prey. The species that live at the bottom of water bodies have a flat body. This helps them move around the ground.
Step 3
The body of most fish is covered with scales that produce mucus, which allows them to maneuver better in the water column. When moving, the fish uses its tail as a rudder, and the lateral fins help it maintain balance. Fish have a special organ - a swim bladder filled with air. Thanks to him, these animals do not drown.
Step 4
Fish, like land animals, breathe oxygen, but they only get it from water. Therefore, their respiratory system is different. Fish swallow water, which then enters the gills. The gills themselves are surrounded by a network of blood vessels. At this point, the oxygen contained in the water enters the bloodstream, and then is transferred to all tissues and organs.
Step 5
Among fish, there are both herbivorous and carnivorous species. Some filter plankton from the water, others dig in the silt, looking for organic debris, and still others feed on algae. Predators, depending on their size, may prefer different types of insects or small crustaceans for food, as well as other fish and even mammals. Omnivorous fish are also found in nature.
Step 6
Fish differ in males and females, and two individuals of different sexes participate in reproduction. In some species, hermaphroditism is common - their representatives can act as both female and male individuals throughout their lives.
