Yuri Frolov, biologist
Photo: © Victor Podolsky / Photobank Laurie.
Figure: Sharon High School.commons.Wikimedia.org.wiki.
Carp (Cyprinus Carpio Carpio) can block some air, popling on the surface, and it will fall into a swimming bubble from the esophagus in the narrow channel. Photo by Sergey Gorlans.
At the perch of the sea (sebastes sp.), As, however, and the river, the bubble is closed and completely separated from the intestine. Photo: jovibor.
The sand shark (family Odontaspididae) does not have a swimming bubble. Its role performs a separate part of the stomach. Photo: Richard Ling / Wikimedia Commons / CC-BY-SA-2.0.
Cambals, like many other bottom fish, cost at all without a swimming bubble. In the photo: Leopard Kambala, or spotted Botus (Bothus Pantherinus). Photo: © Sergey Dubrov / Photobank Laurie.
Everyone knows, at least from adventure and military movies, as maneuvering at the depths of a submarine. She has special tanks, where you can download intricate water or to push it with compressed air. More water - the boat is heavy and plunges deeper, more air - pops up.
For about the same, many fish are also coming. Only the tanks of them are elastic, changing its volume - this is a swimming bubble lying in the abdominal cavity. You probably saw him if you ever watched how to clean fresh fish.
Typical fish is about 5% heavier than water. If it does not make effort, it sinks to the bottom. The swimming bubble equalizes the proportion of the fish with the specific water weight, which allows the fish to hang motionlessly, not popling and not dropping. And in order to not much to change the depth, it is quite slightly working with fins. Adjust the depth, of course, it is necessary on the go. Physiologists have determined that the swimming bubble, maintaining buoyancy at low speed, saves fish to 60% of the effort, and with quick movement - more than 5%. By the way, a person with a shallow breathing has the same proportion as water, and having taken a deep breath, it becomes easier than water. So it's not so easy to drown.
In evolution, the swimming bubble arose from the intestine. Part of the esophagus or stomach alone and began to serve not for nutrition, but to regulate the specific weight of the fish. At this stage of evolution, there is, for example, a sand shark: she has no swimming bubble, but part of the stomach is separate in the form of a pocket, in which shark swallows a little air so as not to sink.
In some fish (for example, salmon, herring, carp) between the swimming bubble and the esophagus, a narrow canal remained. They can, overlooking the surface, stroke into the bubble air, which will allow you to remain in the upper layers of the reservoir. If you need to plunge deeper, the fish can breathe a little.
Other fish (Cod, Ocoon, Heck), the bubble is completely closed and separated from the intestine. In order to think or slightly pull it out, the pump is needed. There are even two such fish pumps, and they are located in the bubble itself. Special iron by means of a cunning biochemical mechanism takes out gases from the blood (and there they fall through the gills from the water - after all, in water, even at high depths of air gases are dissolved) and displays them into a bubble. On the other end of the bubble there is a plot pearated by blood vessels. Through them, gases are transferred back to blood. Both processes go pretty slow.
Why do fish in general change the depth? First of all, in pursuit of food, for example, plankton, which pops up, then immersed. More - to hide from predators who are waiting at a certain depth. Some species float or plunge for spawning, and outside the reproduction period live at the other depth.
Finally, many swimming bubble fish are not at all. These are bottom types, such as Flash, who are quietly floating at the bottom and collect food from it. There is no swimming bubble in cartilage fish - sharks and skates. Perhaps because their skeleton consisting of cartilage, lighter than the bone skeleton of other fish. Hold without a bubble and quickly floating predatory fish, such as tuna, Atlantic mackerel (its speed in the throw reaches 77 km / h). The powerful muscles of these predators allows them to quickly change the depth and resist the immersion. But to bring some general rule - who and why there is a bubble, and who does not have - quite hard. Of two close-friendly species with a similar way, one can not have a bubble, another is completely developed.
Fish has and other ways to reduce the proportion so as not to sink. For example, accumulate fat, because it is lighter than water. So, one of the types of sharks liver is 75% consisting of fat (in mammals in the liver 5% fat). Another option - due to the active work of the kidneys, get rid of heavy salts in the blood and other liquids inside the body. No wonder the seafarers, the victims of the shipwreck, if the boat ended the supply of fresh water, drink juice, squeezed from sea fish: it is almost fresh.
But if some organ of a living organism is, it is necessary to use it as much as possible so that it is not idle in vain. Some fish publish with their bubble sounds, others use it as a resonator to increase hearing sensitivity. A bubble can serve as a depth sensor: when the volume increases, it increases its volume, decreases when immersed, and the nerve endings feel. Finally, the air from the bubble fish can use as a supply for breathing with a sprint sprinkle.
And so what is interesting: light-level vertebrates arose from the swimming bubble of fish, including a person.
One of my relative, very passionate fishing, loved such a delicacy: roasted over the match of the fishing swimming bubble ... I can not judge the advantages of such a dish - but it would be interesting to try, it would be interesting to know what it was ... And even more interesting - figure out what kind of body and why do you need fish?
It occurs in the intrauterine period - and at this time it is an intestinal tube, located above the spine, and at the same time a bubble is associated with an intestinal tube with an air canal. In the future, as the digestive system develops, the esophagus is formed from this section of the intestinal tube. Will the swimming bubble be connected with it? In some species of fish - yes (they are called physotics, or open), and through this channel will include gases, as well as leave it. So the case is at the herring, carp, sturgeon - these fish can adjust the volume of the swimming bubble by switching air.
But there are such fish whose channel connecting a swimming bubble with a digestive system will overgrow. How is the bubble filled with gases in such fish - closed, or physioclists? Of course, nature took care of this: they have a thick plexus of capillaries on the wall of the swimming bubble, it is called a red body. This is through blood passing through these capillaries, and gases are also absorbed. The closed is belonging, for example, pike perch and perch.
How does the swimming bubble "works"? First of all, it is a "hydrostatic apparatus" of fish. The deeper the fish is, the stronger the gas is compressed in its swimming bubble, the more its proportion - and the faster it is immersed. On the contrary, than at a lesser depth is a fish, the more expanding the gas in the swimming bubble, the proportion is less, the stronger the fish is pushed to the surface.
All these pressure changes immediately "learns" the brain of fish, where the nerve endings are sent to the signals located in the walls of the swimming bubble, and in accordance with these signals, the brain "manages" the muscles of the fish.
At a certain depth, the pressure inside and outside aligns - and then the fish does not need to make any movements at all to stay at this depth (from the point of view of hydrostatics this condition is called zero buoyancy). This corresponds to a "natural habitat" of fish, where it spends most of the time. We understand the meaning of such evolutionary acquisition, if we look at the fish, there are no swimming bubble - for example, for sharks. These sea predators are constantly moving, even when they rest - otherwise they will begin to "fall down" in the thickness of the water!
However, with all the utility of the swimming bubble, there are fish to which he would only interfere. As already mentioned, he helps the fish "stabilize" his position in the thickness of water, respectively, to quickly move in the water up and down with it would be not easy, and in those fish that do it constantly, there is no swimming bubble - for example, for mackerel, At Tuna.
Do not need a swimming bubble and deep-sea fish: at great depth the water pressure is such a strong that his swimming bubble would simply be possible - it would push all the gas in two bills!
The hydrostatic function is the main task of the swimming bubble, but not the only one. Some fish - for example, carps and soma - with its help perceive shock and sound waves. And some fish have a swimming bubble source ... Voices. Yes, fish are far from so meld, as it is considered! During World War II, the Americans could not understand for a long time on their submarines for a long time, who publishes urching sounds under water, were looking for enemy submarines, and it turned out - it was trigla fish. And they give their "concerts" with the help of swimming bubbles.
As you can see, the swimming bubble is not as simple as it seems. And most importantly, he had a large evolutionary future: they subsequently formed light, which allowed living beings to go to the land.
It would seem that the answer to this question is obvious: to swim, or rather, to stay at the necessary depth. Bubble for fish. Something like a natural hydrostatic sensor.
Down or up
When the fish is started to the depth, the water pressure on its body immediately increases, the swimming bubble begins to shrink and pushes air out of itself. It happens "automatically", that is, the fish independently do not control the process. The amount of air inside the body decreases and the fish almost does not have to make up effort to be immersed on the depth.
When the fish rises up, everything happens exactly the opposite. Water pressure on the body falls and the bubble is gradually filled with gas, if the fish stops, the bubble will be able to hold it at the desired depth.
The nerve endings that permeate the swimming body transmit the pulses of the central nervous system, and the fish feels: which is depth and what pressure is experiencing, in connection with which it can adjust its movement.
Where does gas come from and what?
Depending on the type of swimming bubble adult fish, they are divided into two groups: closed and open and open. The first bubble is filled with blood gases and gives them also to the vessels, through a special network of capillaries on a thin wall. The open-fiscal fish bubble is a separate organ and is filled after swallowing atmospheric air.
As for the gas that fills the bubble, it is mainly oxygen, hydrocarbon and a certain amount of nitrogen.
Other bubble function
Many ichthyologists will not agree with the statement that the fish "samples" of silenceness, because they can and supply special signals to themselves like, transforming sound waves from water oscillations, and they make it with a swimming bubble.
What fish do not bubble?
Not all the fish acquired this useful body, in the sailboat, many deep-water and bottom fish bubble, and why they need it, if they never try to surface.
Stabilize fish position in water helps swimming bubble, reducing the mass of their body. It is almost a gasproof well stretch and is a characteristic sign of the inner structure of fish. The bubble is filled with a mixture of gases: nitrogen, oxygen and carbon dioxide. Since fish have a higher density than water, the most important function of the swimming bubble is to ensure their buoyancy, that is, they can soar in water and without energy costs without working with fins, remain at the same depth.
Development of a swimming bubble
Swimming bubble It develops in a larvae of fish from the front of the intestine and remains with most freshwater fish throughout life. After hatching of the larvae of fish, there are no gas in the swimming bubble. To fill it, they have to rise to the water surface and suck the air there. Fishes of those species, the swimming bubble of which has a direct connection with the intestines, is called open-value. These include from our fish salmon (siga, goltsy, trout, charies, pikes) and carp (carps, lines, slather, etc.). They are able to quickly fill the swimming bubble with gas and release it again, which allows them to quickly rise from the depth and again dive to the depth.
Fishes, whose intestinal connection is missing, are called closed topus. The swimming bubble is a closed air bag. To regulate gas, there is a so-called gas of iron. RETE MIRABILE ("Wonderful Network") is attached to it, a network of capillaries, which, according to the principle of countercurrent, leads to the gas to the gland and takes away from it.
Gas Iron. It is responsible for increasing the pressure, and the decrease in it provides densely penetrated by the capillaries in the wall of the swimming bubble, called a red body or oval. Since the leveling of pressure from per-rootpuster lasts much longer than the open-to-discovers. They can only slowly rise from deep layers of water, so in these fish, the front intestine due to the strongly inflated swimming bubble is made of mouth, if they are flooded at a depth and quickly remove to the surface. The most famous closed-cubs are perch, pike perch and barley. In some dwelling flooded fish, the swimming bubble is strongly reduced or not completely, som, as a typical representative of the bottom fish, has only a badly formed swimming bubble. A bull-podchanger, which rests between stones and under them in the streams and rivers, does not have a swimming bubble at all. Since he is a bad swimmer, it moves along the bottom with twenty fins placed on the sides.
Swimming bubble as a sense organ
Along with the above, the swimming bubble of many fish also performs other functions, such as the perception of sound and shock waves in Somoms and Karpov. Some fish can reproduce even sounds with a swimming bubble. Most fish reach it using special muscle groups that make the wall of the swimming bubble fluctuate. Gollyans are released by danger from the swimming bubble gas and produce as a result of this sounds that can be perceived by their relatives. From marine fish, first of all, the hill and trigla are known for their grunting and sick sounds. Interesting detail in this regard: During World War II, the loud sounds of trigl caused great confusion among the teams of American submarines. Acoustics nervously crushed enemy boats, until he accidentally noticed that these curious sounds make fish.
The habitat in the water inevitably imposes an imprint on the structure of the body of fish. Not only the overall structure of the structure, but also many system systems designed to ensure the livelihood of fish in the aquatic environment, in their structure, and sometimes on the principles of functioning, differ from those from terrestrial animals. There are those who are unique, that is, not occurring from representatives of other groups of vertebrates.
Among the problems that are facing water organisms in general and in front of the fish in particular, one of the first to significantly is the problem of retention in the thickness of water. Simply put, in front of the fish the question arises "how not to drown?" Really, fish body density, as well as most vertebrates, exceeds water density, Variating for different species within 1.07 - 1.12. Thus, they would have to have a negative buoyancy, which means drowning in water, but we know that this does not happen. In the process of evolution, various groups of fish have developed a number of devices that allow them to compensate for negative buoyancy. Some groups of fish went along the way to reduce the total body density due to an increase in tissue with low density, such as adipose tissue, others acquired a specialized organ - swimming, or gas, bubble. About his structure and operation and will be discussed in this post.
Location of the swimming bubble in the body of fish
So, the classic definition of the swimming bubble as follows:
The swimming bubble is a gas filled with a gas in front of the intestines, the main function of which is to ensure the buoyancy of fish.
In this definition, you should pay attention to two points. Firstly, nothing is said in it about the situation of the grow out - despite the fact that the overwhelming majority of species it is dorsal, that is, it is laid from the dorsal side of the body (which is sometimes noted in the definition of the swimming bubble). However, it does not happen in all groups of fish - a small number of taxa has a ventral increase. Secondly, the phrase "basic function" with a semantic stripping on the "basic" - the swimming bubble can perform many different functions, and the hydrostatic in different groups of fish is not the only one, and sometimes the main one. Read more about this below.
Swimming bubble in different groups of fish
First of all, I remind you that we determined that the fish are called the team of water vertebrates, which throughout their lives have gills, and the fines of the finable type are used for movement. As you can see, nothing about the swimming bubble, as an integral characteristic of fish in this definition, is not said. Why did it happen, because the swimming bubble does not occur in other animal groups and is characterized only for fish? The answer is simple - the fact is that this body has, firstly, not all groups of fish, but, secondly, even in those groups for which it is peculiar to, there are species that have lost it in the process of evolution as a more unnecessary body.
The main modern large cycons of fish in relation to the presence / absence of a swimming bubble and functions performed are characterized as follows:
Headhead (Mine ends and mixins) - The swimming bubble is absent
Cartilage (sharks, skates, chimeras) - there is no swimming bubble
Coxicantic (Lathemeria) - Swimming bubble reduced
Two-plating - there is a breath body
Multidoral - there is a breathing body
Cartilage ganoids (sturgeon) - There is a hydrostatic organ
Bone ganoids - there is a breath body
Kostyish fish - is available, in some reduced, hydrostatic organ, in a small number of types of respiratory body
Swimming bubble and light ground vertebrates
From the above review, it is possible to detect an interesting tendency - in evolutionarily more ancient groups of fish, the swimming bubble is the body of breathing, and only in more modern groups it acquires the function of the hydrostatic organ. To understand the logic of these transformations, it is necessary to refer to the biology of the now living representatives of the ancient groups of fish and their fossil ancestors. Now the living species inhabit, as a rule, weakly flowing, stagnant or even drying water, in which they are not rarely found with the problem of a lack of oxygen dissolved in water. Similar conditions existed in the reservoirs of the Devonian period (about years ago), when their ancestors evolved. Such conditions forced fish to look for other sources of oxygen. The only such source was atmospheric air, which these forms could collect from the surface of the water and then "absorb" in the front of the intestine. As we know, the effectiveness of this absorption is higher than in the large area it goes - this is exactly what the evolution towards an increase in the first part of the intestine, which led to the appearance of a separate increase, and then to an increase in its surface area. The end result of these processes was the appearance of light ground animals, the origin of which according to modern ideas is associated with the evolution of the swimming bubble when the land is out. Thus, the answer to the question "what was primary in a functional plan of a light or swimming bubble" is "light" - apparently, it is a respiratory (respiratory) function preceded by hydrostatic.
Ordinary carp
Interestingly, the acquisition of a swimming bubble performing the function of breathing occurred in different groups of fish independently. Such a conclusion can be made when comparing its position relative to the digestive tube, for example, in multidistral and bone ganoids, which demonstrates us two different ways of forming a swimming bubble. In a multiderail, a swimming bubble is a ventral (located to the bubble from the digestive tract), while bone ganoids (shell pike, amia), the ancestors of which were probably evolved into the same era that the ancestors of multidiscovers, this increase is dorzal. In both groups, the connection of the swimming bubble with the intestines is maintained through a special channel, which has the same location that the increase in the volume of the ventral, the bone Ganoids dozal. Otherwise, these structures are similar. Multide swimming bubble resembles light ground animals and is considered the most primitive arranged. This is a two-bladed increase, the inner surface of which has a practically smooth structure with a small amount of folds. In bone ganoids, the swimming bubble is also two-bladed, but its inner surface has many ridges to increase the surface through which oxygen penetration can occur. In another ancient group of fish, fossil isfalls and their currently living descendant of latimaria - the swimming bubble was formed as a central growth of the intestines. It is also necessary to note the similarity of the position of the swimming bubble of meatless and light ground vertebrates, which is also located ventral. This similarity is not a coincidence - it is the meatlessness that made a revolution in the animal world, coming to the land and giving the beginning of the entire land vertebral life.
Early Evolution of the Swimming Bubble
Gradually, with a change in the ancient climate and the development of ocean fish, the respiratory function of the swimming bubble was lost and hydrostatic was in the first place. As we remember, all modern groups of bony fish have a little exception, a swimming bubble - a dorzal unpalaring increase. Its position is favorably different from ventral, because in the first case the dasal location center of gravity of the body is shifted down, which makes the position of the body in the water medium more stable. There is no doubt that most modern fish swimming bubble evolved from the dozal increase, which was their ancestors. However, it also does not find significant contradictions and the hypothesis, which in a number of groups a swimming bubble could "rewrite" from the abdominal side to the dorsal. The most remarkable thing is that this process we can observe in some modern species, in which the structure of the swimming bubble intermediate between the dorzal and ventral location. So in fish genus of the Erythrinus bubble, although it is located mercenary, but is connected by a duct descending from the lateral part of the intestine. We observe an even more interesting structure at a two-way Neoceratodus fish, in which the swimming bubble is also dorzal, but the channel connecting it from the central part of the digestive tube and turns to the top, the rich intestine. At the same time, it is also observed "wrapping" of the entire system - blood supply vessels and nerves go down, then under the intestine and only after that they go up to the swimming bubble.
Visually different variants of the position of the swimming bubble of fish are presented in the figure below.