Due to the fact that every creature is endowed with respiratory organs, we all get something without which we cannot live - oxygen. In all land animals and humans, these organs are called lungs, which absorb the maximum amount of oxygen from the air. The respiratory system of fish, on the other hand, consists of gills that 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 this biological species is so different from all backbone terrestrial creatures. Well, let's consider all the structural features of fish, their respiratory system and other vital organs.
Fish in brief
To begin with, let's try to figure out what kind of creatures they are, how and by what they live, what kind of relationship they have with a person. Therefore, now we begin our biology lesson, the topic is "Sea fish". This is a superclass of vertebrates that live exclusively in the aquatic environment.environment. A characteristic feature is that all fish are jawed and also have gills. It is worth noting that these indicators are typical for each type of fish, regardless of size and weight. In human life, this subclass plays an economically important role, since most of its representatives are eaten.
It is also believed that fish were at the dawn of evolution. It is these creatures that could live under water, but did not yet have jaws, were once the only inhabitants of the Earth. Since then, the species has evolved, some of them have turned into animals, some have remained under water. That's the whole lesson of biology. The topic "Sea fish. A brief excursion into history" is considered. The science that studies marine fish is called ichthyology. Let's now move on to studying these creatures from a more professional point of view.
General structure of fish
Generally, we can say that the body of each fish is divided into three parts - head, body and tail. The head ends in the region of the gills (at their beginning or end, depending on the superclass). The body ends on the line of the anus in all representatives of this class of marine life. The tail is the simplest part of the body, which consists of a rod and a fin.
The shape of the body strictly depends on the living conditions. Fish that lives in the middle water column (salmon, shark) has a torpedo-shaped figure, less often - swept. The same marine inhabitants that swim above the very bottom have a flattened shape. These can be attributedflounder, sea foxes and other fish that are forced to swim among plants or stones. They take on a more agile shape that has much in common with snakes. For example, an eel is the owner of a very elongated body.
The business card of a fish is its fins
Without fins it is impossible to imagine the structure of a fish. Pictures that are presented even in children's books certainly show us this part of the body of marine inhabitants. What are they?
So, the fins are paired and unpaired. Pairs include chest and abdominal, which are symmetrical and move synchronously. Unpaired are presented in the form of a tail, dorsal fins (from one to three), as well as anal and adipose, which is located immediately behind the dorsal. The fins themselves are composed of hard and soft rays. It is on the basis of the number of these rays that the fin formula is calculated, which is used to determine a specific type of fish. The location of the fin is determined in Latin letters (A - anal, P - thoracic, V - ventral). Further, Roman numerals indicate the number of hard rays, and Arabic - soft.
Classification of fish
Today, conditionally, all fish can be divided into two categories - cartilaginous and bone. The first group includes such inhabitants of the sea, the skeleton of which consists of cartilage of various sizes. This does not mean at all that such a creature is soft and incapable of movement. In many representatives of the superclass, cartilage hardens, and in its densitybecome almost like bones. The second category is bony fish. Biology as a science claims that this superclass was the starting point of evolution. Once within its framework there was a long-extinct lobe-finned fish, from which, perhaps, all land mammals originated. Next, we will take a closer look at the structure of the body of the 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 hard and durable cartilage. Each compound is impregnated with calcium s alts, thanks to which strength appears in cartilage. The notochord 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. Fins are also attached to it - caudal, paired ventral and pectoral. The jaws are located on the ventral side of the skeleton, and above them are two nostrils. The cartilaginous skeleton and muscular corset of such fish are covered on the outside with dense scales, which are called placoid. It consists of dentin, which is similar in composition to ordinary teeth in all terrestrial mammals.
How cartilage breathes
The respiratory system of cartilaginous fish is represented primarily by gill slits. They number from 5 to 7 pairs on the body. Oxygen is distributed to the internal organs thanks to a spiral valve that stretches along the entire body of the fish. A characteristic feature of all cartilaginous is that they lack a swim bladder. Exactlytherefore, they are forced to constantly be in motion, so as not to sink. It is also important to note that the body of cartilaginous fish, which a priori live in s alty waters, contains a minimal amount of this very s alt. Scientists believe that this is due to the fact that this superclass has a lot of urea in the blood, which consists mainly of nitrogen.
Bone bones
Now let's look at what the skeleton of a fish belonging to the superclass of bones looks like, and also find out what else is characteristic of representatives of this category.
So, the skeleton is presented in the form of a head, a torso (they exist separately, unlike the previous case), as well as paired and unpaired limbs. The cranium is divided into two sections - cerebral and visceral. The second includes the jaw and hyoid arches, which are the main components of the jaw apparatus. Also in the skeleton of bony fish there are gill arches that are designed to hold the gill apparatus. As for the muscles of this type 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 already become clear to everyone that the respiratory system of bony fish mainly consists of gills. They are located on the gill arches. Gill slits are also an integral part of such fish. They are covered with a lid of the same name, which is designed so that the fish can breathe even in an immobilized state (unlikecartilaginous). Some representatives of the bone superclass can breathe through the skin. But those that live directly under the surface of the water, and at the same time never go deep, on the contrary, they capture air with their gills from the atmosphere, and not from the aquatic environment.
Structure of gills
Gills are a unique organ that was previously inherent in all primary water creatures that lived on Earth. It is the process of gas exchange between the hydro-environment and the organism in which they function. The gills of the fish of our time are not much different from those that were inherent in the earlier inhabitants of our planet.
As a rule, they are presented in the form of two identical plates, which are penetrated by a very dense network of blood vessels. An integral part of the gills is the coelomic fluid. It is she who performs the process of gas exchange between the aquatic environment and the body of the fish. Note that this description of the respiratory system is inherent not only in fish, but in many vertebrate and non-vertebrate inhabitants of the seas and oceans. But about what is special about those respiratory organs that are in the body of fish, read on.
Where the gills are located
The respiratory system of fish is mostly concentrated in the throat. It is there that the gill arches are located, on which the organs of gas exchange of the same name are fixed. They are presented in the form of petals that pass through themselves both air and various vital fluids that are inside each fish. In certain places, the pharynx is piercedgill slits. It is through them that the oxygen passes, which enters the mouth of the fish with the water it swallows.
A very important fact is that compared to the body size of many marine life, their gills are quite large for them. In this regard, in their bodies there are problems with the osmolarity of the blood plasma. Because of this, fish always drink sea water and release it through the gill slits, thereby speeding up various metabolic processes. It has a lower consistency than blood, therefore it supplies the gills and other internal organs with oxygen faster and more efficiently.
The breathing process itself
When a fish is first born, almost all of its body breathes. Blood vessels permeate each of its organs, including the outer shell, because oxygen, which is in sea water, constantly penetrates into the body. Over time, each such individual begins to develop gill breathing, since it is the gills and all adjacent organs that are equipped with the largest network of blood vessels. This is where the fun begins. The breathing process of each fish depends on its anatomical features, therefore in ichthyology it is customary to divide it into two categories - active breathing and passive breathing. If everything is clear with the active one (the fish breathes “usually”, taking oxygen into the gills and processing it like a person), then we will now try to figure it out in more detail with the passive one.
Passive breathing and what it depends on
This type of breathing is peculiar only to fast-moving inhabitants of the seas and oceans. As we saidabove, sharks, as well as some other representatives of the cartilaginous superclass, cannot be motionless for a long time, since they do not have a swim bladder. There is another reason for this, namely, this is passive breathing. When a fish swims at high speed, it opens its mouth and water automatically enters. Approaching the trachea and gills, oxygen is separated from the liquid, which nourishes the body of a marine fast-moving inhabitant. That is why, being without movement for a long time, the fish deprives itself of the opportunity to breathe, without spending any strength and energy on it. Finally, we note that such fast-moving inhabitants of s alt waters include mainly sharks and all representatives of mackerels.
Main muscle of fish
The structure of the fish heart is very simple, which, we note, has practically not evolved in the entire history of the existence of this class of animals. So, this body they have two chambers. It is represented by one main pump, which includes two chambers - the atrium and the ventricle. The fish heart pumps only venous blood. In principle, the circulatory system of this species of marine life has a closed system. 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 rest of the internal organs. After that, the "waste" blood is collected in the veins (there are two of them in fish - hepatic and cardiac), from where it goes directly to the heart.
Conclusion
That's the end of our short lessonbiology. The theme of fish, as it turned out, is very interesting, fascinating and simple. The organism of these inhabitants of the sea is extremely important for study, since it is believed that they were the first inhabitants of our planet, each of them is the key to unraveling evolution. In addition, studying the structure and functioning of the fish organism is much easier than any other. And the sizes of these inhabitants of the water stochia are quite acceptable for detailed consideration, and at the same time, all systems and formations are simple and accessible even for school-age children.
