Fish units and their features

Fish are vertebrates that live in ponds and breathe in gills. In the world of them there are more than 3 thousand species. It is believed that it was they who first came to the land, giving birth to land animals. What classes and orders of fish exist? How do they differ from each other? To which group does the fish-moon belong - the heaviest fish in the world? We will answer all of these questions in this article.

What is unique about fish?

Fish are an integral part of many ecosystems and important participants in food chains. They are widely distributed on the planet, inhabiting salty and fresh water from the oceans to the high-mountain lakes located at an altitude of more than 6 kilometers.

Most of the life they spend in the water, so the main respiratory apparatus for them are the gills. In many orders of fish there are representatives who are able to climb out for a short time to the surface (mud plow, anabas, flying fish). Some even developed additional respiratory organs - lungs (lungfish - protopterus, corpuscle, etc.).

Practically constant life under water demanded special adaptations from fish. Their outer covers are represented by scales - plates of dentine, cosmin or gaonin, which are superimposed on each other like tiles.

They move with the help of fins, and to reduce the body their body has a streamlined shape. Many fish have a swim bladder. Adjusting the pressure, it promotes vertical movements of the animal in the water column, and also helps to keep it at a certain depth.

Fish classification

Pisces is a group of chordates, within which several classes are distinguished. In different sources their number diverges. Usually they are divided into cartilaginous and bone. Sometimes Bony fishes stand out as a superclass, and within it distinguish classes of ray-finned and lopastoper.

Detachments of cartilaginous fishes are chimera-like, katranoobraznye, stingray-like, sea angels, multi-branched, globular and friend. There are about 13 of them, but they are represented by different kinds of sharks, rays and chimeras.

The skeleton of these fish is composed of cartilage. Skates and sharks do not cover the gills with a lid, but they come out with slots outwards. The swim bladder is absent, which forces them to constantly be in motion, otherwise they will fall to the bottom. Individual species do not lay eggs, but multiply by live birth.

Bodily fish classes are more numerous. As the name implies, their skeleton is made of bones. Gills are part of the skeleton, they consist of petals and stamens, and are covered with caps on top.

In one article, it is impossible to list all the fish units at once, so below we will describe the most interesting or common ones.

Perciformes

The largest group of fish, which covers about 7-8 thousand species. Most of them are commercial. The main feature of the fish of the group of perciforms is the ctenoid scales. Its edges are not even, but are divided into many small denticles. The pectoral fins are located under the thoracic fins, and some of the fin fins are turned into thorns.

Perciformes vary greatly in size. Some species reach only a few centimeters (Lutian mystic), while others grow to 3 meters (blue tuna). Typical representatives are mackerel, bullhead, zander, tuna, gourami, swordfish. But the sea perch to them do not belong and belong to the group of scorpion-shaped.

Chimeras

Fish detachment chymereobraznyh have a somewhat bizarre appearance. Their body is elongated and severely narrowed to the bisped tail. Before the two dorsal fins there is a spine, which can be hidden in the crease on the back.

The nasal part is pointed and has a triangular shape. In some species it is strongly elongated, and resembles a proboscis. The mouth is located below. Pectoral fins large and shaped like wings.

Chimeras swim slowly, "hovering" in the water. These are benthic fish that live at great depths or shelf shallows. They are found in the Indian, Atlantic and Pacific oceans. Propagation by laying eggs.

Sturgeon

Structurally, the sturgeon occupy an intermediate position between the cartilaginous and bony detachments of fish. Usually they are classified as a class of bony radiant fishes and a subclass of cartilaginous fishes . These include the beluga, all kinds of sturgeon, kaluga, sterlet, etc.

Their skeleton consists of cartilages, possesses a chord and is not divided into vertebrae. The body of the fish is elongated and covered with five rows of large bone plates, between which are located smaller scales. The mouth is located at the bottom. In front of him are four antennae, which play the role of organs of touch.

Sturgeon species inhabit the rivers and seas of the Northern Hemisphere. Fishing for them is very common, especially caviar is valued. These are quite large fish. Beluga, for example, reach 4-9 meters, sturgeons - 6 meters.

Bobbin-like

This group of bony fishes includes about 250 species. Most representatives have an unusual body shape: spherical, flat discoid, cubic, etc. The mouth of the fish is usually small, the bones of the upper jaw tightly closed. Instead of the usual scales, their bodies are covered with thorns or small needles.

They inhabit warm ocean waters near the equator, preferring coral reefs. Bright representatives are fish-hedgehog, fish-moon, body-cube and others. The fish-moon is the heaviest fish in the world. Its weight can exceed 20 tons. It has a disk-shaped shape, flattened from the sides and reaches up to 2 meters in diameter.

Flounder

Flounder - flat fish floating on their sides. They also lie on their sides, so their eyes are placed only on one side. Color, as a rule, is close to the coloring of the seabed. This is necessary for camouflage, because almost all the fish of the order are predators and feed on crustaceans, mollusks and small fishes.

They inhabit the seas from the tropical to the temperate zones, mostly up near the bottom. Fish prefer shallow water, hotel species easily swim in the mouth of rivers. These include flounder, halibut, and a team. The sizes of the smallest representatives are 7-8 centimeters, the largest - about 5 meters.

Celery

Celery are one of the most primitive orders of bone fish. Their body is slightly flattened and covered with scales of semicircular shape. The skull of many fish consists of cartilaginous tissue. The rays of the fins are very soft, which is why the detachment is often called "soft". The detachment includes the Atlantic menhaden, Baltic herring, Pacific, Sardine, sprats, anchovies, Baltic herring, sprat.

These fish are very diverse in lifestyle, many are able to make long migrations. They are distributed in all oceans of the world, especially in tropical regions and subtropical regions. The circumpolar regions inhabit only certain species, some also live in fresh water bodies. The majority refers to pelagic fish - living in the upper layers of the ocean.

Angular

Unusual representatives of bony fishes are a group of eels. Because of the long, elongated body, they can be confused with snakes. However, the body of the eel-like does not taper to the tail and is often not even flattened from the sides.

They move wriggling. There are no fins in the fins of the pelvic fins, just like the scales. The skin is covered with mucus. Like snakes, they may not have ribs, and the ridge is up to 300 vertebrae. Most of the eels are poisonous and predators. Especially large species (giant moray eels) even attack reef and tiger sharks.

These are marine fish that prefer warm water. They are represented by a variety of moray eels and eels. The only freshwater family is the river acne. They live in water bodies that belong to the basins of the Atlantic, Pacific and Indian Ocean.

Gray sharks

Among all the sharks, the most numerous is a squad of carcass or gray sharks. It includes more than 250 species, including a hammerhead, a tiger, a silk, a blunt shark, etc. Its representatives are considered one of the most dangerous inhabitants of the sea depths. On their account, many human victims.

They live in the coastal zones of the seas of the tropical, subtropical and temperate zones. Fish constantly move, then retiring into the depths of the ocean, then swimming in the shallows. Some species also appear in fresh water bodies.

Gray sharks have five pairs of gill slits, two dorsal and one anal fin. They reproduce either by laying eggs or by live birth.

They have a large mouth located below, and the snout is extended forward. For some sharks, it is strongly rounded (in blunt sharks). Specific species is a hammerhead. Their muzzle is flattened from above and wide from the sides, resembling the front edge of the hammer. The first dorsal fin is curved in the shape of a sickle.