What is the class of fish? Distinctive features, structure, reproduction of fish

Beluga, carp, herring, trout, carp, thick bean, carp - all known fish. This list can be continued indefinitely. And their commercial importance can not be overestimated. Indeed, the fish class is very diverse. Modern taxonomy includes more than 20 thousand species of these aquatic animals. Due to what signs of the structure they managed to master this habitat and take the dominant position in it. To what class are the fish that differ in their structure? These and other questions are answered in our article.

Signs of fish

Knowingly confident people say: "It feels like a fish in the water." Scientists know that the first fish lived in the Silurian period. Outwardly they looked like modern sharks with movable jaws, on which were placed sharp teeth. Millions of years passed, in the course of evolution, the fish changed and acquired a number of new adaptive features.

Like aquatic animals, they all have a streamlined body shape, completely or partially covered with scales, different fin types are located on the body, and respiratory organs are the gills. These are common signs for all representatives of a given systematic unit. But what class fish are related to, you can answer, considering their significant differences. At the moment, there are two: Bony and Cartilaginous.

Features of external structure

The body of all fish is covered with scales. It protects the skin of aquatic inhabitants from excessive friction of water. After all, most of them spend most of their life in motion. An additional protection against rubbing is also a large amount of mucus, which is rich in skin. This helps to survive many species under adverse conditions of temporary drought. Not all types of fish body completely scaled. For example, in sharks, it is located in one row on the surface of the body, resembling their teeth in appearance. The same can be said of the numerous representatives of the sturgeon. Most of the bone fish are protected by scales, like a strong shell. It also performs additional functions: disguise from predators, warning coloration in predatory and poisonous species, denotation of sexual characteristics, reflection of light in water.

Structure of the fins

The next characteristic feature of fish is the presence of fins. These formations serve as limbs for movement in water, and some ancient species can even crawl with their help. Fins are grouped into two groups. The first are paired: the abdominal and thoracic. They contribute to maintaining the balance of fish in the water column. Tail, anal and dorsal are unpaired. They work like a rudder, directing the body of aquatic animals in the right direction. As a result of evolution, the extremities of reptiles developed from the fins of fish.

On the body of fish, you can easily see the sideline. It is a unique organ of balance and touch, characteristic only for fish.

Internal structure of fish

Their features related to the aquatic habitat, and have systems of organs of these animals. Musculoskeletal is represented by a skeleton. Depending on the class, it is formed by a cartilaginous or osteal tissue. All bones of the skeleton of the head are connected immovably, except the lower jaw. This allows fish to easily capture prey. The structure of this department of the skeleton also includes gill covers and arches, to the latter of which the respiratory organs of the fish - the gills - are attached. The axial skeleton consists of separate vertebrae connected with each other and with the skull motionless. The ribs are attached to the trunk part of the spine. The skeleton of fins is represented by rays. They are also formed by bone tissue. But the paired fins also have belts. To them are attached the muscles, which move them.

Digestive system of fish through type. It begins with the oropharyngeal cavity. Most fish on the jaws have sharp teeth that serve to grab and tear food. In the process of digestion also involved enzymes of the glands - liver and pancreas. In the processes of isolation and salt metabolism, the main role in the body of fish is played by paired kidneys. Outward they open with the help of ureters.

Fish are cold-blooded animals. This means that the temperature of their body depends on the changes taking place in the environment. This sign is determined by the circulatory system. It is represented by a two-chambered heart and a closed vessel structure. During their movement, venous and arterial blood are mixed.

The nervous system is represented by the brain and spinal cord and nerves. And its peripheral part - nerve fibers. The cerebellum reaches a special development in the brain. This part determines the rapid and coordinated movements of fish. The sensory organs are able to perceive any irritations possible in the aquatic environment. Since the eye lens of fish does not change its shape and position, animals can see only a short distance. But at the same time they are able to discern both the shape and color of various objects. The organ of sound perception is represented by the inner ear and is associated with the structure responsible for the equilibrium.

Reproduction of fish also has its own characteristics. These animals are dioecious, with an external type of fertilization.

What is spawning

The process of reproduction of fish is also called spawning. It occurs in the water. The female spawns eggs, and the male water it with seminal fluid. As a result, a fertilized egg is formed. As a result of successive mitotic divisions, an adult develops from it.

Sometimes reproduction of fish is associated with spawning migrations and significant changes in the behavior and structure of fish during this period. For example, pink salmon form large herds, in which they move from the seas to the upper reaches of rivers. During this trip they have to overcome many obstacles, moving against the current. These fish have a hump on their back, the jaw is twisted and twisted. Having lost a lot of strength, after the fertilization process, adult individuals die. Surprisingly, young fry return to their own habitat.

Groups of fish

The huge species diversity necessitated the classification of this group of animals. At present, scientists have accurately determined the characteristics by which the Pisces class can be classified. The systematic accessory is determined by the presence of a swim bladder, gill slits or lids, and the type of scales. So you can distinguish between bone and cartilaginous fish. There are other signs that these animals are grouped together. For example, fish that move to spawn for other habitats are called walkways. But, given the scope, distinguish between commercial and decorative representatives of these aquatic animals.

Cartilaginous fish

To what class are the fish having a cartilaginous skeleton, gill slits opening outward? It's not difficult to guess. This cartilaginous fish. They do not have a swimming bladder, so they either live on the bottom, or are constantly in motion. Fish-saw, white, giant, whale sharks, stingray-tail ... You know such fish. List of dangerous predators can be continued by the sea devil, the electric ramp and the sea fox. These marine life are a great danger to the life of animals and humans. Although there are quite innocent specimens among cartilaginous fishes. Thus, the shark katran eats fish and crustaceans. In addition to the frightening appearance, it does not represent any danger to a person.

Bone fishes

On the question of which class the fish are most numerous, perhaps every schoolboy will answer. Their skeleton consists entirely of bone tissue. The swim bladder located in the body cavity allows its holders to be kept in the water column. Gills are covered with gill covers, and do not open outward through separate apertures. Bone fish have such characteristics.

Meaning of fish

Representatives of this superclass of vertebrates primarily have important commercial importance. Man consumes their nutritious meat and protein-rich caviar. And the number of recipes for cooking different species does not know the account. Fish oil has long been used as a remedy for the treatment of bacterial and viral respiratory diseases. A person annually catches a large number of individuals and breeds them independently. Meat is also obtained from meat and bones. It is used as fertilizer and feed for many domestic animals.

Recently, more and more popular sport fishing, attracting participants from different countries. And just to catch a goldfish that fulfills all desires, every one of us dreams for sure!

Thus, to which class fish are classified, it is possible to determine by the features of their structure, organization and way of life.