The world of fish is very diverse, as is their habitat. They live in oceans, seas, rivers and lakes; they can exist both in warm tropical regions and in the cold waters of the Arctic Ocean. How are they different from other animals? What species and families of fish are there?
What do we know about fish?
Approximately 70% of the Earth is covered with 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 s alt 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 with scales - densely spaced plates that act as protection. Their body temperature is not constant, but depends on the environment.
There are fish that live near the surface of the water, others live in reefs or at the bottom. Swimming occurs due to the muscles. They are divided into "slow", responsible for measured movement and drift, and "fast" for instantaneous reactions. Maneuvers are carried out thanks tofins, and deep movements - to the swim 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, snake-like (for example, eel or moray). Some of them are covered with thorns (hedgehog fish), others are even devoid of scales. Some species are able to briefly climb trees, burrow into the ground or fly over the surface of the water.
Fish are a group of jawed animals belonging to the chordates. Their classifications often change due to the discovery of new species. Currently, they are divided into three classes: cartilaginous, ray-finned and lobe-finned. The last two are included in the superclass of bones.
They can also be divided into subclasses, superorders, orders, families, genera and species. The families of fish are numerous. They combine several genera close in shape, color, number and size of fins. Of the commercial fish, the most famous are the families of salmon, horse mackerel, eels, herring and others.
Lobe-finned
These fish are the closest to their ancient ancestors. The class appeared about 300 million years ago. Its representatives were the first to move into inland waters, which contributed to better protection from predators and the preservation of special features.
Lobe-finned fish have modern and archaic features in structure. Wide fins allow you to move along the bottom and overcome short distances to other water bodies. Specialan outgrowth in their esophagus has become a lung, allowing them to hold their breath.
The most famous representatives are the Latimeriaceae family. These are lobe-finned fish, which for many years were considered extinct about 60 years ago. In 1938, the coelacanth was caught off the coast of South Africa and named after Marjorie Courtenay-Latimer, who discovered it.
Ray-finned fish
The bony fish class is the most common, comprising more than 93% of all fish. Their sizes range from a few millimeters to 10-12 meters. Like many bones, they have a swim bladder responsible for hydrostatics, respiration, and sound production. It helps fish to stay at certain depths without much effort, as well as move from the bottom to the surface.
The structural features of ray-finned fish are characterized by the absence of a chord (longitudinal axis of the skeleton), unlike lobe-finned ones. Only the bony spine is present. Scales are sometimes replaced by bone plates. The fins are paired, there are up to three of them on the back. There are no internal nasal openings.
These are numerous fish. The class includes more than two hundred families. This includes both well-known perches, sturgeons, gobies, as well as bizarre anglerfish, triggerfish. The latter have a beautiful spotted or striped color. Near the dorsal fin, they have three spikes, one of which works as a trigger, fixing the other two.
Cartilaginous fish
Class cartilaginous fishdiffers primarily in the structure of the skeleton, which consists of many cartilages. They are deprived of a swim bladder, therefore they are kept in the water column with an exclusively active movement. Most cartilaginous fish do not lay eggs, but give birth to young.
The structure of the gills is also peculiar. They are not covered by a gill cover, as in bony fish, and go outside. Some species breathe through their mouths, while others use spiracles and gills. The chemical composition of their teeth is similar to that of a human.
Representatives of the class are stingrays and well-known sharks. Stingrays have a somewhat flattened body, large pectoral fins, and an elongated thin tail. Animals grow from a few centimeters to seven meters long. Electric rays have special organs capable of delivering a discharge of current 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 of them have an excellent sense of smell. The great white shark, for example, can smell one drop of blood several meters away.
Unusual fish
The heaviest of all bony fish is the moonfish. It grows up to three meters in length. The animal is laterally flattened and shaped like a disk with two protruding fins. Its color is brown or dark gray. The largest copy weighs 2 thousand kilograms and at the same time reaches 4.2 meters in height.length.
The seahorse is a fish, although it bears little resemblance to it. It swims vertically, shaped like a chess piece of a knight. A close relative is the leafy sea dragon. Its translucent, overgrown fins resemble a plant.
Napoleon fish belongs to the wrasse 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.
