The overclass Bone fish belongs to the class of vertebrate animals and includes two more classes. One of them is represented by radiant fish. It consists of more than 30 units and 500 families. The second - lobed-feather fish (double-breathing and brush-headed).
Bone fish live in all waters of the Earth - in salty and fresh, from both poles to the equator. They are common both offshore and in the most inaccessible depths of the seas and oceans. Both bone and cartilaginous fish have fins, that is, paired limbs. However, bone-cartilaginous fish have significant distinguishing features. First of all, this applies to the skeleton and head: they have these parts are completely bony. The cover of these fish is exactly the same - the scales formed by bone plates.
The bony branchial arches of these fish (there are five pairs) are located on the sides of the pharynx. On them are gills in the form of drooping petals. The nostrils are paired, in the inner ear there are semicircular canals (there are three of them). The structure of the fish of this superclass is distinguished by a gill cavity covered by a bone gill cover. The swim bladder is located inside the body, in its upper part. The grasping jaws together with the teeth form a mouth. The length of these fish varies widely: from 70 to 500-700 cm, respectively, their weight ranges from several kilograms to one and a half tons.
Bone fish first appeared approximately 400 million years ago. Gradually, compared with other fish and vertebrates living on earth, they reached the greatest variety. Mostly bone fish have a body shape resembling a torpedo. But there are also arrow-shaped fish (saury, garfish, barracuda, pike), ribbon-like (vogmera, moray eels, chained, blackheads) and spherical (bodies, sea devils, puffers). And the sea horse resembles a chess horse figure at all. Fins, both paired and unpaired, help fish regulate body position. The main organ of their movement is the tail. Although some of the fish (for example, the moon, sea needle, triggerfish) change their location due to the undulating movements of unpaired fins. On the head and on both sides of the body, bone fish have a so-called lateral line - a sensitive organ equipped with channel pores. It is peculiar only to animals living in the water. The sideline helps them perceive the strength and direction of the flow. Thanks to this, even blinded fish can circumvent obstacles and catch prey.
The back of almost all representatives of this superclass is colored darker than the sides, and the belly is the lightest area on the body of the fish. This color has a protective function. It is difficult to distinguish a dark back on the surface of the water, when viewed from above, from the air. And if you look at the fish from below, towards the firmament, it is not easy to notice a light abdomen. The color depends on where and how deep the fish live. As a rule, its color repeats their environment. There is another type of protective color: bright circles, stripes on the body, spots on the tail, reminiscent of the eyes. All this disorients both the enemy and the prey, since the shape of the fish’s body is visually deformed, its contours are broken into pieces. In addition, coloring serves as a means of identifying individuals of their species, including the other sex.
Some bone fish are able to jump out of the water while flying in the air for more than a hundred meters. Many of them even in the bladder or gill cavity appeared such devices that allow them to stay out of the water for quite a long time in humid tropical air. And in multi-feather and double-breathing fish, the swimming bladder consists of cells. This semblance of the lungs allows them to breathe even atmospheric air.
Bone fish play a huge role in the practical life of man. In many countries, fishing is one of the main sectors of the economy. Fish is not only healthy and tasty food. It serves as an excellent raw material for medicines (fat), feed for poultry and livestock (feed flour), fertilizers for land (fat), glue, technical fat and other products that are used in food and light industries.