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 the cold waters of the Arctic Ocean. What is their difference from other animals? What species and families of fish exist?
What do we know about fish?
About 70% of the Earth is covered in water, which is the main home for these amazing creatures. The world of fish consists of 20 thousand species. They are excellent swimmers and inhabit fresh and salty water bodies. To find food, fish are able to travel considerable distances.
These animals breathe with the help of gills, which are present in them throughout all stages of development. The body of most fish is covered by scales - densely arranged plates that serve as a defense. Their body temperature is not constant, but depends on the environment.
There are fish that live at the very surface of the water; others live in reefs or at the bottom. Swimming is due to the muscles. They are divided into “slow”, responsible for measured movement and drift, and “fast” for instant reactions. Maneuvers are carried out thanks to the fins, and deep movements - to the swimming bladder (only in some fish).
Species diversity and classification
No group of vertebrates has such a wide range of body shape and color as fish. They can be oval, round, flat, serpentine (for example, eel or moray eel). Some of them are covered with thorns (hedgehog fish), others are even devoid of scales. Some species are able to climb trees for a short time, bury themselves in the ground or fly over the surface of the water.
Fish represent a group of maxillary animals belonging to chordates. Their classifications often change in connection with the discovery of new species. Currently, they are divided into three classes: cartilaginous, ray-feathered, and lapelopera. The last two are included in the superclass of bone.
They can also be divided into subclasses, superorders, orders, families, genera and species. Families of fish are numerous. They combine several close in shape, color, number and size of the fin of the genera. Of the commercial fish, the most famous are the families of salmon, horse mackerel, eel, herring and others.
Lobe
These fish are closest to their most ancient ancestors. The class appeared about 300 million years ago. Its representatives were the first to go into inland waters, which contributed to better protection from predators and the preservation of special features.
Lobatepera fish have modern and archaic features in the structure. Wide fins allow you to move along the bottom and overcome small distances to other bodies of water. A special outgrowth in their esophagus turned into a lung, so that they can hold their breath.
The most famous representatives are the Latimeria family. These are brushfish, which for many years were considered extinct about 60 years ago. In 1938, coelacanth was caught off the coast of South Africa and named after Marjorie Courtenay-Latimer, who discovered it.
Rayfin fish
The bone fish class 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 bones, they have a swimming bladder responsible for hydrostatics, respiration and the formation of sounds. It helps fish stay at certain depths without much effort, as well as move from bottom to surface.
The structural features of ray-finned fish are characterized by the absence of a chord (the longitudinal axis of the skeleton), in contrast to the lobed-nosed. Only the bone spine is present. Scales are sometimes replaced by bone plates. Fins are paired, on their back there are up to three. There are no internal nasal openings.
These are numerous fish. The class includes more than two hundred families. This includes both perch, sturgeon, goby, as well as fancy anglerfish, triggerfish, known to all. The latter have a beautiful spotty or striped color. Near the dorsal fin, they have three spikes, one of which works like a trigger, fixing the other two.
Cartilaginous fish
The class of cartilaginous fish differs primarily in the structure of the skeleton, which consists of many cartilages. They are deprived of a swimming bladder, therefore they are held in the water column by exclusively active movement. Most cartilaginous fish do not lay eggs, but give birth to cubs.
The structure of the gills is also peculiar. They are not covered by a branchial lid, like bone fish, and go outside. Some species breathe through the mouth, while others use sprays and gills. The chemical composition of their teeth is similar to human.
Representatives of the class are stingrays and well-known sharks. Stingrays have a somewhat flattened body, large pectoral fins, an elongated thin tail. Animals grow from a few centimeters to seven meters long. Electric slopes have special organs that can give a current discharge of up to 250 volts.
Sharks include over 450 species. Their sizes range from 15 centimeters to 20 meters. The largest representative is the 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 have a great sense of smell. A white shark, for example, can smell one drop of blood in a few meters.
Fancy fish
The hardest of all bone 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 instance weighs 2 thousand kilograms and at the same time reaches 4.2 meters in length.
Seahorse is a fish, although it does not resemble it very much. He swims vertically, similar in shape to a chess piece of a horse. A close relative is a leafy sea dragon. Its translucent overgrown fins resemble a plant.
Napoleon fish belongs to the Gubanov family, which is not in vain. She has huge full lips. It got its name because of an unusual outgrowth on the forehead, similar to the imperial cocked hat.