Pisces (class): description. Fish families

The world of fish is very diverse, as is their habitat. They live in oceans, seas, rivers and lakes, can exist both in warm tropical regions and in cold waters of the Arctic Ocean. What makes them different from other animals? What kinds and families of fish exist?

What do we know about fish?

Approximately 70% of the Earth is covered with water, which is the main house for these amazing creatures. The world of fish consists of 20 thousand species. They are excellent swimmers and inhabit fresh and salt water. To find food, fish are able to travel long distances.

These animals breathe with the help of the gills, which are present during all stages of development. The body of most fish covers scales - densely located plates, performing the role of protection. The temperature of their body is not constant, but depends on the environment.

There are fish that live near the surface of the water, others live in reefs or on the bottom. Swimming takes place at the expense of muscles. They are divided into "slow", responsible for the measured movement and drift, and "fast" for instantaneous reactions. Maneuvers are carried out thanks to the fins, and deep displacements to the swim bladder (only for a part of the fish).

Species diversity and classification

No group of vertebrates has such a wide range of shape and coloration as the fish. They can be oval, round, flat, snake-like (eg, eels or moray eels). Some of them are covered with spines (fish-hedgehogs), others are devoid of even scales. Individual species can climb for a short time on trees, burrow into the ground or fly over the surface of the water.

Fish represent a group of maxillary animals belonging to chordates. Their classifications often change due to the discovery of new species. At present, they are divided into three classes: cartilaginous, ray-rayed and lopostere. The latter two enter the superclass of the bone.

They can also be subdivided into subclasses, commandos, detachments, families, genera and species. Families of fish are numerous. They combine several closely related in shape, color, number and size of the fins of labor. Among the commercial fish, the families of salmonids, horse mackerel, eel-like, herrings and others are the most known.

Lopastepere

These fish are the closest to their ancient ancestors. The class appeared about 300 million years ago. Its representatives were the first to move to inland water bodies, which contributed to better protection from predators and the preservation of special features.

Lopasteper fishes have modern and archaic features in the structure. Wide fins allow you to navigate the bottom and cross small distances to other water bodies. A special outgrowth in their esophagus has turned into a lung, so they can hold their breath.

The most famous representatives are the family of the latimeric. These are cysteper fish, which for many years were considered extinct approximately 60 years ago. In 1938, the coelacanth was caught off the coast of South Africa and named in honor of Marjorie Courtenay-Latimer, who discovered it.

Lacerated fish

The class related to bone fishes is the most common and includes more than 93% of all fish. Their sizes range from a few millimeters to 10-12 meters. Like many bone, they have a swim bladder responsible for hydrostatics, breathing and sound formation. It helps fish to keep at certain depths without much effort, and also to move from bottom to surface.

The features of the structure of the ray-finned fishes are characterized by the absence of a chord (the longitudinal axis of the skeleton), in contrast to the lobe-hopper. Only the bony spine is present. Scales are sometimes replaced by bone plates. The fins are paired, on the back they are up to three. There are no internal nasal apertures.

These are numerous fish. The class includes more than two hundred families. This includes both percussion, sturgeon, bovine, and bizarre anglers, spinogors. The latter have a beautiful spotted or striped color. Near the dorsal fin, they have three spines, one of which acts as a trigger, fixing the other two.

Cartilaginous fish

The class of cartilaginous fishes differs first of all in the structure of the skeleton, which consists of a multitude of cartilages. They are devoid of a swimming bladder, therefore they are kept in the water column by an exceptionally active movement. Most cartilaginous fish do not lay eggs, but give birth to young ones.

The structure of the gills is also peculiar. They are not covered with a gill cover, as in bone fishes, and come out. Some species breathe through the mouth, others use splashes and gills. The chemical composition of their teeth is similar to the human.

Representatives of the class are skates and all known sharks. The skates have a somewhat flattened body, large pectoral fins, elongated thin tail. Animals grow from a few centimeters to seven meters in length. Electric rays have special bodies capable of producing a current discharge of up to 250 volts.

Sharks include more than 450 species. Their sizes range from 15 centimeters to 20 meters. The largest representative is a whale shark. It feeds on plankton and is not dangerous to humans. Many other species of this sea monster, on the contrary, are predators. Most of them have an excellent sense of smell. White shark, for example, is able to catch the smell of one drop of blood for a few meters.

Unusual fish

The heaviest of all the bony fish is the moon fish. It grows to three meters in length. The animal is flattened laterally and resembles a disk with two protruding fins. Its color is brown or dark gray. The largest specimen weighs 2,000 kilograms and reaches 4.2 meters in length.

The seahorse is a fish, although it does not much remind it. He swims vertically, in shape similar to the chess piece of a horse. A close-in relative is a deciduous sea dragon. Its translucent overgrown fins resemble a plant.

The Napoleon fish belongs to the family of the Guban, which is not in vain. She has huge full lips. Its name was received because of an unusual outgrowth on the forehead, similar to the imperial cocked hat.