Respiratory system of fish. Features of the structure of fish

Due to the fact that each creature is endowed with respiratory organs, we all get what we can not live without - oxygen. In all terrestrial animals and humans, these organs are called lungs, which absorb the maximum amount of oxygen from the air. The respiratory system of fish consists of gills, which draw oxygen into the body from the water, where it is much less than in the air. It is because of this that the structure of the body of a given biological species is so different from all spiny terrestrial beings. Well, let's consider all the features of the structure of fish, their respiratory system and other vital organs.

Briefly about fish

First, let's try to understand what kind of creatures they are, how they live and what they have to do with a person. Because now we are starting our lesson in biology, the theme "Sea fish". This is a superclass of vertebrates, which live exclusively in the aquatic environment. A characteristic feature is that all fish are chelated, and also have gills. It is worth noting that these indicators are characteristic for each fish species, regardless of size and mass. In human life, this subclass plays an economically important role, since most of its representatives are used for food.

It is also believed that the fish were at the dawn of evolution. It was such creatures that could live under water, but did not yet have jaws, once were the only inhabitants of the Earth. Since then, the species evolved, some of them turned into animals, some remained under water. That's the whole lesson of biology. The theme "Sea Fish: A Brief History" was considered. The science that studies marine fish is called "ichthyology". Let us now proceed to study these creatures from a more professional point of view.

General scheme of the structure of fish

Summarized, we can say that the body of each fish is divided into three parts - the head, trunk and tail. The head ends in the region of the gills (at their beginning or end - depends on the superclass). The trunk ends in the line of the anus at all representatives of this class of marine life. The tail is the simplest part of the body, which consists of a stem and a fin.

The shape of the body is strictly dependent on the habitat. The fish that lives in the middle of the water (salmon, shark), has a torpedo shape, more rarely - arrow-shaped. The same sea inhabitants that swim above the bottom, have a flattened shape. They include flounder, sea fox and other fish that are forced to swim among plants or stones. They acquire more maneuverable outlines, which have much in common with snakes. For example, the eel is the owner of a very elongated body.

Business card of fish - its fins

Without fins, it is impossible to imagine the structure of the fish. Pictures that are presented even in children's books, certainly show us this part of the body of the marine inhabitants. What are they?

So, the fins are paired and unpaired. For paired we can include thoracic and abdominal, which are symmetrical and synchronous. Unpaired are presented in the form of a tail, dorsal fins (one to three), as well as anal and fat, which is located just behind the dorsal. In themselves fins consist of hard and soft rays. It is based on the number of these rays that the fin formula is calculated, which is used to determine the specific type of fish. Latin letters determine the location of the fin (A - anal, P - thoracic, V - ventral). Further, Roman numerals indicate the number of hard rays, and Arab - soft.

Fish classification

Today, conventionally, all fish can be divided into two categories - cartilaginous and bony. The first group includes such inhabitants of the sea, the skeleton of which consists of their cartilages of various sizes. This does not mean that such a creature is soft and unable to move. In many representatives of the superclass the cartilage hardens, and in density become almost like bones. The second category is bone fish. Biology as a science claims that it was this superclass that was the starting point of evolution. Once upon a time there was a long-extinct bristling fish, from which, possibly, all terrestrial mammals originated. Next, we will consider in more detail the structure of the body of fish of each of these species.

Cartilaginous

In principle, the structure of cartilaginous fish is not something complicated and unusual. This is an ordinary skeleton, which consists of very solid and strong cartilage. Each compound is impregnated with calcium salts, due to which in the cartilage and appears strength. Chorda keeps its shape throughout life, while it is partially reduced. The skull is connected to the jaws, as a result of which the skeleton of the fish has an integral structure. To it fins - caudal, paired abdominal and thoracic - are also attached. Jaws are located on the ventral side of the skeleton, and above them are two nostrils. The cartilaginous skeleton and the muscular corset of such fish are covered on the outside with dense scales, called placoid. It consists of dentine, which in its composition is similar to ordinary teeth in all terrestrial mammals.

How the cartilaginous breathe

The respiratory system of fish of the supra-class of the cartilaginous is represented primarily by gill slits. They have from 5 to 7 pairs on the body. In the internal organs, oxygen is distributed through a spiral valve that extends along the entire body of the fish. A characteristic feature of all cartilaginous is that they do not have a swim bladder. That's why they are forced to constantly be on the move so as not to go to the bottom. It is also important to note that in the body of cartilaginous fish, which a priori live in saline waters, contains a minimum amount of this salt itself. Scientists believe that this is due to the fact that in the blood of this superclass there is a lot of urea, which consists mainly of nitrogen.

Bony

Now let's look at the skeleton of the fish that belongs to the superclass of the bone, and also learn what the representatives of this category are still characteristic of.

So, the skeleton is represented in the form of a head, trunk (they exist separately, unlike the previous case), as well as paired and unpaired limbs. The cranial box is divided into two sections - cerebral and visceral. The second includes the jaw and sublingual arches, which are the main components of the jaw apparatus. Also in the skeleton of bone fish there are gill arches, which are designed to hold the gill apparatus. As for the muscles of this species of fish, they all have a segmental structure, and the most developed of them are the jaw, fin and gill.

Respiratory apparatus of bone inhabitants of the sea

Probably, it has become clear to everyone that the respiratory system of fish of the supra-class bone is mainly composed of gills. They are located on gill arches. Also an integral part of these fish are the gill slits. They are covered with the same cap, which is designed to allow the fish to breathe even in immobilized condition (in contrast to cartilaginous). Some representatives of the supraclavicular bone can breathe through the skin. But those that live directly under the surface of the water, and while never deep down, on the contrary, capture the air with their gills from the atmosphere, and not from the aquatic environment.

Structure of the gills

Gills - a unique organ that was previously inherent in all primary creatures that lived on Earth. In it there is a process of gas exchange between the hydro environment and the body in which they function. The gills of fish of our time differ little from those gills that were characteristic of earlier inhabitants of our planet.

As a rule, they are presented in the form of two identical plates, which are permeated with a very dense network of blood vessels. An integral part of the gills is coelomic liquid. It is she who performs the process of gas exchange between the aquatic environment and the fish organism. Note that this description of the respiratory system is inherent not only to fish, but to many vertebrate and non-vertebral inhabitants of the seas and oceans. But that's what is special about the respiratory organs that are in the body of the fish, read on.

Where gills are located

The respiratory system of fish is mostly concentrated in the pharynx. It is there that the gill arches are located on which the same bodies of gas exchange are fixed. They are presented in the form of petals, which let through and air, and various vitally necessary fluids that are inside each fish. In certain places the pharynx is perforated by gill slits. It is through them that the oxygen that passes into the mouth of the fish with the water swallowed by it passes.

A very important fact is that in comparison with the size of the organism of many marine inhabitants, their gills are very large for them. In this regard, their organisms have problems with osmolarity of the blood plasma. Because of this, fish always drink sea water and release it through the gill slits, thereby speeding up the various metabolic processes. It has a less consistency than blood, therefore it supplies the gills and other internal organs with oxygen faster and more efficiently.

The very process of breathing

When the fish is just born, almost all of her body breathes. Blood vessels permeate each of its organs, including the outer shell, because oxygen, which is in seawater, penetrates into the body constantly. Over time, each such individual begins to develop gill respiration, since the largest mesh of blood vessels is equipped with gills and all adjacent organs. Here then the fun begins. The process of breathing of each fish depends on its anatomical features, therefore in ichthyology it is customary to divide it into two categories - active respiration and passive. If everything is clear with the active one (the fish breathes "normally", picking up oxygen in the gills and treating it like a person), then with the passive we now try to understand in more detail.

Passive breathing and on what it depends

This type of breathing is peculiar only to high-speed inhabitants of the seas and oceans. As we said above, sharks, as well as some other representatives of the cartilaginous superclass, can not remain without movement for a long time, since they do not have a swim bladder. There is one more reason for this, namely, this is passive breathing. When the fish swims at high speed, it opens the mouth, and there automatically gets water. Approaching the trachea and gills, oxygen separates from the liquid, which feeds the organism of the sea fast-moving inhabitant. That is why, for a long time without fish, the fish deprive themselves of the opportunity to breathe without spending any energy and energy on it. Finally, we note that such fast-moving inhabitants of saline waters are mainly sharks and all representatives of mackerel.

The main muscle of the body of fish

Very simple is the structure of the heart of the fish, which, we note, throughout the history of the existence of this class of animals, has not evolved. So, this organ is two-chambered. It is represented by one main pump, which includes two chambers - the atrium and the ventricle. The fish heart pumps only the venous blood. In principle, the circulatory system in this species of marine life has a closed system. The blood circulates through all the capillaries of the gills, then merges in the vessels, and from there again diverges into smaller capillaries that already supply the remaining internal organs. After that, the "spent" blood is collected in the veins (there are two of them - liver and cardiac), from which it already comes directly to the heart.

Conclusion

So our brief lesson in biology came to an end. The theme of fish, as it turned out, is very interesting, fascinating and simple. The organism of the data of the inhabitants of the sea is extremely important for studying, since it is believed that they were the first inhabitants of our planet, each of them is the key to unraveling the evolution. In addition, it is much easier to study the structure and functioning of the fish organism than any other. And the sizes of these inhabitants of the water are quite acceptable for detailed consideration, and all systems and formations are simple and accessible even for school-age children.