Fish are vertebrates that live in ponds and breathe through gills. In the world there are more than 3 thousand species. It is believed that they were the first to land, giving rise to land animals. What classes and orders of fish exist? How do they differ from each other? Which unit is the moon fish - the heaviest fish in the world? We will answer all 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 widespread on the planet, inhabiting salty and fresh water bodies from the oceans to high-altitude lakes located at an altitude of more than 6 kilometers.
They spend most of their life in water, so the gills are their main breathing apparatus. In many orders of fish there are representatives who are able to crawl to the surface for a short time (mud jumper, pineapple, flying fish). Some even developed additional respiratory organs - the lungs (double-breathing fish - protopterus, horned tooth, etc.).
Almost constant life under water required special adaptations from the fish. Their outer covers are represented by scales - plates of dentin, cosmine or gaonin, which are superimposed on each other, like tiles.
They move with the help of fins, and to reduce the body, their body is streamlined. Many fish have a swim bladder. By regulating the pressure, it promotes vertical movements of the animal in the water column, and also helps them stay at a certain depth.
Fish classification
Fish is a group of chordate animals, within which several classes are distinguished. In various sources, their number diverges. They are usually divided into cartilage and bone. Bone fish are sometimes distinguished as a superclass, and within it, classes of ray-fin and lap-finned are distinguished.
The orders of cartilaginous fish are chimera-shaped, katranoobraznye, stingrays, angelfish, multi-gill, laminae and friend. There are about 13 of them, and various species of sharks, stingrays and chimeras represent them.
The skeleton of these fish is composed of cartilage. In stingrays and sharks, the gills do not hide behind the lid, but go out with cracks. There is no swimming bubble, which forces them to constantly be in motion, otherwise they will fall to the bottom. Some species do not lay eggs, but reproduce by live birth.
Bonefish class units 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 lids on top.
It is impossible to list all fish orders in one article at once, so below we will describe the most interesting or common ones.
Perch
The largest detachment of fish, which covers about 7-8 thousand species. Most of them are fishing. The main peculiarity of perch-like fish is ctenoid scales. Its edges are not even, but divided into many small cloves. The pectoral fins are located under the pectoral fins, and part of the radial fins are turned into spines.
Perch vary greatly in size. Some species reach only a few centimeters (Lucian mystihtis), while others grow up to 3 meters (bluefin tuna). Typical representatives are mackerel, bulls, pike perch, tuna, gourami, swordfish. But the sea bass do not belong to them and belong to the group of scorpion-like.
Chimeras
Chimera-shaped fish have a somewhat bizarre appearance. Their body is elongated and strongly narrowed to the spine tail. In front of the two dorsal fins is a spike that can hide in a crease on the back.
The nose is pointed and triangular in shape. In some species, it is very elongated, and resembles a proboscis. The mouth is located below. The pectoral fins are large and shaped like wings.
Chimeras slowly swim, "soaring" in the water. These are bottom fish living at great depths or shelf shallows. They are found in the Indian, Atlantic and Pacific Oceans. Propagate by laying eggs.
Sturgeon-like
By structure, sturgeons occupy an intermediate place between cartilaginous and bony orders of fish. Usually they are classified as a class of bony- finned fish and a subclass of cartilage. These include beluga, all kinds of sturgeons, kaluga, sterlet, etc.
Their skeleton consists of cartilage, has 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 there are smaller scales. The mouth is located below. Before him are four antennae, playing the role of the organs of touch.
Sturgeons inhabit the rivers and seas of the Northern Hemisphere. Fishing for them is very common, caviar is especially appreciated. These are quite large fish. Beluga, for example, reach 4-9 meters, sturgeons - 6 meters.
Pufferfish
This squad of bone fish includes about 250 species. Most representatives have an unusual body shape: spherical, flattened disk-shaped, cubic, etc. The mouth of the fish is usually small, the bones of the upper jaw are tightly closed. Instead of ordinary scales, spikes or small needles cover their body.
They inhabit warm oceanic waters near the equator, preferring coral reefs. Bright representatives are hedgehog fish, moon fish, box cube and others. Moonfish is the heaviest fish in the world. Its weight can exceed 20 tons. It has a disk-shaped shape, flattened laterally and reaches up to 2 meters in diameter.
Flatfish
Flatfish - flat fish swimming on their sides. They also lie on their side, so their eyes are placed only on one side. Color, as a rule, is close to the color of the seabed. This is necessary for camouflage, because almost all fish of the order are predators and feed on crustaceans, mollusks and small fish.
They inhabit the seas from tropical to temperate zones, living mainly near the bottom. Fish prefer shallow waters, hotel species easily swim in the estuaries. These include flounder, halibut, limanda. The dimensions of the smallest representatives are 7-8 centimeters, the largest - about 5 meters.
Herring
Herring-like represent one of the most primitive orders of bone fish. Their body is slightly flattened and covered with semicircular scales. The skull of many fish consists of cartilage. The rays of the fins are very soft, which is why the squad is often called "soft-feathers". The order includes the Atlantic Menheden, Baltic herring, Pacific herring, sardine, sprats, anchovies, herring, sprat.
These fish are very diverse in lifestyle, many are able to make long migrations. They are common in all the oceans of the world, especially in tropical regions and subtropical regions. Subpolar regions are inhabited only by individual species, some also live in fresh water bodies. Most relate to pelagic fish - living in the upper layers of the ocean.
Eel-like
Unusual representatives of bone fish - a group of eel-like. Due to the long, elongated body, they can be confused with snakes. However, the eel-like body does not taper towards the tail and is often not even flattened laterally.
They move meanderingly. Fish have no ventral fins, just like scales. The skin is covered with mucus. Like snakes, they may not have ribs, and the ridge is up to 300 vertebrae. Most eels are poisonous and predators. Especially large species (giant moray eels) even attack reef and tiger sharks.
These are marine fish that prefer warm ponds. They are represented by various types of moray eels and eels. The only freshwater family is river eels. They live in reservoirs that belong to the basins of the Atlantic, Pacific and Indian Ocean.
Gray sharks
Among all sharks, the most numerous is the detachment Karharid or gray sharks. It includes more than 250 species, including a hammerhead shark, tiger, silk, blunt shark, etc. Its representatives are considered one of the most dangerous inhabitants of the deep sea. On their account a lot of human victims.
They live in the coastal zones of the seas of the tropical, subtropical and temperate zones. Fish are constantly moving, then moving away into the depths of the ocean, then swimming in shallow water. Some species also appear in fresh water bodies.
Gray sharks have five pairs of gill slits, two dorsal and one anal fin. They breed either by laying eggs, or by live birth.
They have a large mouth located below, and the snout is stretched forward. In some sharks, it is strongly rounded (in blunt sharks). The hammerhead shark has a specific look. Their muzzle is flattened from above and wide from the sides, reminiscent of the front edge of the hammer. The first dorsal fin is curved in the shape of a sickle.