Swim bladder. Description of the swim bladder in fish Where is the swim bladder in fish

The fish body is quite complex and multifunctional. The ability to stay under water while performing swimming maneuvers and maintaining a stable position is determined by the special structure of the body. In addition to organs that are familiar even to humans, the body of many underwater inhabitants contains important parts that allow them to provide buoyancy and stabilization. Of significant importance in this context is the swim bladder, which is a continuation of the intestine. According to many scientists, this organ can be considered as a predecessor of human lungs. But in fish it performs its primary tasks, which are not limited only to the function of a kind of balancer.

Formation of the swim bladder

The development of the bladder begins in the larva, from the foregut. Most freshwater fish retain this organ throughout their lives. At the time of release from the larva, there is still no gaseous composition in the bubbles of the fry. To fill it with air, the fish have to rise to the surface and independently capture the necessary mixture. At the stage of embryonic development, the swim bladder is formed as a dorsal outgrowth and is located under the spine. Subsequently, the canal that connects this part to the esophagus disappears. But this does not happen in all individuals. Based on the presence or absence of this channel, fish are divided into closed- and open-vesical. In the first case, the air duct becomes clogged, and gases are removed through the blood capillaries on the inner walls of the bladder. In open-vesical fish, this organ is connected to the intestine through an air duct, through which gases are eliminated.

Gas filling of the bladder

Gas glands stabilize the pressure of the bladder. In particular, they help to increase it, and if it is necessary to decrease it, the red body, formed by a dense capillary network, is activated. Since pressure equalization in open-vesical fish occurs more slowly than in closed-vesical species, they can quickly rise from the water depths. When catching individuals of the second type, fishermen sometimes observe how the swim bladder protrudes from the mouth. This is due to the fact that the container inflates under conditions of rapid rise to the surface from depth. Such fish include, in particular, pike perch, perch and stickleback. Some predators that live at the very bottom have a greatly reduced bladder.

Hydrostatic function

The fish bladder is a multifunctional organ, but its main task is to stabilize the position in different conditions under water. This is a function of a hydrostatic nature, which, by the way, can be replaced by other parts of the body, which is confirmed by examples of fish that do not have such a bladder. One way or another, the main function helps fish stay at certain depths, where the weight of the water displaced by the body corresponds to the mass of the individual itself. In practice, the hydrostatic function can manifest itself as follows: at the moment of active immersion, the body contracts along with the bubble, and when ascent, on the contrary, it straightens out. During the diving process, the mass of the displaced volume is reduced and becomes less than the weight of the fish. Therefore, the fish can go down without much difficulty. The lower the dive, the higher the pressure becomes and the more the body is compressed. Reverse processes occur at the moment of ascent - the gas expands, as a result of which the mass is lighter and the fish rises upward with ease.

Functions of the senses

Along with its hydrostatic function, this organ also acts as a hearing aid in some way. With its help, fish can perceive noise and vibration waves. But not all species have this ability - carp and catfish are included in the category with this ability. But sound perception is provided not by the swim bladder itself, but by the whole group of organs to which it belongs. Special muscles, for example, can provoke vibrations of the walls of the bladder, which causes sensations of vibration. It is noteworthy that in some species that have such a bladder, hydrostatics are completely absent, but the ability to perceive sounds is preserved. This applies mainly to those who spend most of their lives at one level under water.

Protective functions

In moments of danger, minnows, for example, can release gas from their bladder and produce specific sounds that are distinguishable by their relatives. At the same time, you should not think that sound production is primitive in nature and cannot be perceived by other inhabitants of the underwater world. Croakers are well known to fishermen for their purring and grunting sounds. Moreover, the swim bladder that trigl fish have literally terrified the crews of American submarines during the war - the sounds made were so expressive. Typically, such manifestations occur during moments of nervous overstrain in fish. If, in the case of the hydrostatic function, the operation of the bubble occurs under the influence of external pressure, then sound formation occurs as a special protective signal, generated exclusively by fish.

What fish do not have a swim bladder?

Sailfish are deprived of this organ, as well as species that lead a bottom-dwelling lifestyle. Almost all deep-sea individuals also do without a swim bladder. This is exactly the case when buoyancy can be provided by alternative means - in particular, thanks to fat accumulations and their ability not to shrink. Low body density in some fish also contributes to maintaining positional stability. But there is also another principle for maintaining hydrostatic function. For example, a shark does not have a swim bladder, so it is forced to maintain a sufficient depth of immersion through active manipulation of its body and fins.

Conclusion

It is not without reason that many scientists draw parallels between the fish bladder. These parts of the body are united by an evolutionary relationship, in the context of which it is worth considering the modern structure of fish. The fact that not all fish species have a swim bladder makes it controversial. This does not mean at all that this organ is unnecessary, however, the processes of its atrophy and reduction indicate the possibility of doing without this part. In some cases, fish use internal fat and the density of the lower body for the same hydrostatic function, and in others they use fins.

Material from Wikipedia - the free encyclopedia

Swim bladder- a gas-filled outgrowth of the anterior part of the intestine, the main function of which is to ensure the buoyancy of fish. The swim bladder can perform hydrostatic, respiratory and sound-producing functions.

In bony fishes, it is absent in sailfishes, as well as in bottom-living and deep-sea fish. In the latter, buoyancy is provided mainly by fat due to its incompressibility or due to the lower body density of the fish, such as in ancistrus, golomyanok and drop fish. During the process of evolution, one of the structures similar to the swim bladder was transformed into the lungs of terrestrial vertebrates. The closest variant to the lungs of tetrapods, however, is demonstrated not by teleosts, but by bony fish (multi-feathered, having unpaired cellular lungs - the lower outgrowth of the pharynx) and lungfishes (three modern representatives show diversity in the structure of the lungs). After all, the lungs of terrestrial vertebrates originated from the lower outgrowth of the pharynx, and the swim bladder of teleosts - from the upper outgrowth of the esophagus.

Swim bladder in different groups of fish

Not all groups of fish have a swim bladder, and in those groups for which it is characteristic, there are species that have lost it during evolution. The main modern large taxa of fish with respect to the presence or absence of a swim bladder and its functions are characterized as follows:

Cyclostomes and cartilaginous animals lack a swim bladder. Coelacanths (coelacanth) - the swim bladder is reduced. Double-breathing, multi-feathered - there is a respiratory organ. Cartilaginous ganoids (sturgeon-shaped) - present, hydrostatic organ. Bone ganoids - present, respiratory organ. Bony fish have a hydrostatic organ, or in some it is reduced, and in a small number of species it is a respiratory organ.

Description

During the embryonic development of fish, the swim bladder appears as a dorsal outgrowth of the intestinal tube and is located under the spine. With further development, the canal connecting the swim bladder to the esophagus may disappear. Depending on the presence or absence of such a channel, fish are divided into open- and closed-vesical. In open bladder fish ( physostome) the swim bladder is connected throughout life to the intestines by an air duct through which gases enter and exit. Such fish can swallow air and thus control the volume of the swim bladder. Open bladders include carp, herring, sturgeon and others. In adult closed-vesical fish ( physical sheets) the air duct becomes overgrown, and gases are released and absorbed through the red body - a dense plexus of blood capillaries on the inner wall of the swim bladder.

Hydrostatic function

The main function of the swim bladder in fish is hydrostatic. It helps the fish stay at a certain depth, where the weight of the water displaced by the fish is equal to the weight of the fish itself. When the fish actively falls below this level, its body, experiencing greater external pressure from the water, contracts, squeezing the swim bladder. In this case, the weight of the displaced volume of water decreases and becomes less than the weight of the fish and the fish falls down. The lower it falls, the stronger the water pressure becomes, the more the fish’s body is compressed and the faster its fall continues. On the contrary, when ascending closer to the surface, the gas in the swim bladder expands and reduces the specific gravity of the fish, which pushes the fish even more towards the surface.

Thus, the main purpose of the swim bladder is to provide zero buoyancy in the fish’s usual habitat, where it does not have to spend energy maintaining its body at this depth. For example,

The swim bladder of a fish is an outgrowth of the esophagus.

The swim bladder helps the fish stay at a certain depth - the one at which the weight of the water displaced by the fish is equal to the weight of the fish itself. Thanks to the swim bladder, the fish does not spend additional energy maintaining its body at this depth.

The fish is deprived of the ability to voluntarily inflate or contract its swim bladder. If a fish submerges, the water pressure on its body increases, it is compressed, and the swim bladder contracts. The lower the fish falls, the stronger the water pressure becomes, the more the fish’s body is compressed and the faster its fall continues. And when the fish rises to the upper layers, the water pressure on it decreases, and the swim bladder expands. The closer the fish is to the surface of the water, the more the gas in the swim bladder expands, which reduces the specific gravity of the fish. This pushes the fish further towards the surface.

So, the fish cannot regulate the volume of its swim bladder. But in the walls of the bladder there are nerve endings that send signals to the brain as it contracts and expands. Based on this information, the brain sends commands to the executive organs - the muscles with which the fish moves.

Thus, a fish's swim bladder is its hydrostatic apparatus, ensuring its balance: it helps the fish stay at a certain depth.

Some fish can make sounds using their swim bladder. In some fish it serves as a resonator and transducer of sound waves.

By the way...

The swim bladder appears during the embryonic development of fish as an outgrowth of the intestinal tube. In the future, the canal that connects the swim bladder to the esophagus may remain or become overgrown. Depending on whether the fish has such a channel, all fish are divided into openvesical And closedvesical. Open bladder fish can swallow air and thus control the volume of the swim bladder. Open bladder fish include carp, herring, and sturgeon. In closed-vesical fish, gases are released and absorbed through a dense plexus of blood capillaries on the inner wall of the swim bladder - the red body.

The story about the swim bladder was mainly about its position relative to the intestine in different groups of fish, as well as the paths of possible evolution from the primary ventral lung of ancient fish to the real dorsal swim bladder of modern fish. Today we will take a closer look at the internal structure of this organ and once again return to the diversity of its structure.

Previously, we noted that in the evolution of fish from ancestral (often primitive) to modern, more complex forms, there is a tendency, firstly, to the loss of connection between the swim bladder and the intestine and, secondly, to a general complication of its structure. Indeed, the youngest taxa are, as a rule, closed-vesical, while older ones (having an earlier evolutionary origin) are open-vesicular.

Diagram of the structure of a fish swim bladder

The transition from open-vesical to closed-vesicality took place in evolution through gradual thinning and lengthening of the air canal and a shift in the place of its connection with the digestive tract from the pharynx to the hind intestines. Thus, in modern open-vesical fish this canal is long and narrow, as, for example, in salmonids, and opens behind the stomach, and in the armored pike Lepisosteus - a representative of one of the ancient groups - it is short and wide, and opens into the esophagus. This “front” position shortens the path into the swim bladder for air swallowed from the surface of the water and ensures respiratory function.

How the swim bladder works

First, let's talk about the principle of operation of the swim bladder as a hydrostatic organ. This principle is simple: by changing the volume of the swim bladder, the fish changes the overall density of the body, and as a result, its buoyancy changes. How does the volume of the swim bladder change? The first researchers believed that this is carried out only due to the muscles surrounding the swim bladder, the work of which leads to its compression or stretching, which in turn expels air from the bladder or, on the contrary, forces it inside. However, this is not true - a change in the volume of the swim bladder solely due to the work of muscles is characteristic of only a few primitive shallow-water forms. In the vast majority of fish, specialized internal structures located in the bladder itself are used for this, while muscles are used in extreme cases. These structures, depending on the advancement of the taxon, can be expressed to varying degrees, but two types are always distinguished - the red body and the oval. In fact, these are two zones in the membrane of the swim bladder that perform the functions of synthesis (red body) and removal (oval) of gases. The functioning of these zones is associated with abundant blood circulation, since blood is the main one for most fish, and in the case of closed-vesical fish, the only transport “channel” for gases during filling and emptying of the swim bladder.

Now let's take a little closer look at the structure of these two "working" zones.

The structure of the red body

Let's start with red body (lat. corpus ruber), which is essentially a gas gland (and in the English-language literature it is mainly called that way), which serves to “pump” gases from the blood into the cavity of the swim bladder. It is a collection of secretory cells (probably of epithelial origin) and capillaries. In different groups of fish, the red body can be expressed differently - it can cover either the entire surface of the bladder, or only a small part of it, have a lobed structure or be a homogeneous formation, and be lined with multilayered or single-layered epithelium.

The red body looks like a dense accumulation of copillaries

Now I will not dwell on the details of the operation of the entire system, but for further understanding of the structure of the red body, it is necessary to note that the passage of gases directly from the blood into the swim bladder by simple diffusion is impossible due to the difference in their partial pressures. To overcome this difference, secretory cells are needed, which, due to the chemical reactions occurring in them, ensure the transport of gases in the desired direction. To synthesize the required volume of gases, secretory cells must be adequately supplied with blood, which is precisely the source of these gases. Therefore, the most important component of the red body is a cluster of capillaries that form a dense network in the wall of the swim bladder and received a rather funny and seemingly not entirely scientific name - a wonderful network from the Latin rete mirabile. As noted above, in different species of fish the wonderful network, as an integral part of the red body, can be developed to varying degrees, however, if present, it is built according to one universal principle. This principle consists of a very close arrangement of capillaries that bring blood to the secretory cells and take it back. Along these close arterial and venous capillaries, parallel (but multidirectional) blood transport occurs, which provides a complex mechanism for pumping partial pressure of gases in the afferent capillaries and the very possibility of “pumping” gases into the swim bladder. I will try to tell you more about this in a separate post, but for now I suggest you just look at the figure below, which shows the microstructure of the wonderful network and the paths of gases in its different parts.

The microstructure of a wonderful network and the difference in partial pressures of gases in its different sections.

The arrows show the direction of gases and blood flow.

Two types of wonderful networking

Speaking about the structure of a wonderful network, one cannot fail to mention that there are two types of organization of parallel afferent and efferent capillaries. The miraculous network can be bipolar, when two micronetworks of capillaries are located in series, or unipolar, when there is only one micronetwork of capillaries directly adjacent to the secretory cells. These construction options are shown in the figure below. In most fish, the wonderful network is built according to the unipolar type, while in eels it is bipolar. Differences in the structure of the wonderful network are also manifested in the fact that the number of pairs of capillaries (1 incoming + 1 outgoing) in a micronetwork can vary among different species from a few to several thousand.

Unipolar and bipolar types of miraculous network structure

Oval structure

Now let's move on to the structure of the oval, which is the structure responsible for the transport of gases from the swim bladder into the blood. The oval is a section of the wall of the swim bladder, abundantly supplied with vessels, as is the case with the red body, forming a dense network. The structure of this network, however, is much simpler, since the mechanism of reverse transport of gases from the swim bladder to the blood is much simpler. Due to the difference in partial pressures, gases penetrate into the blood according to the principle of direct diffusion, therefore, to ensure this process, no secretory cells and the organization of parallel transport in capillaries are required. The speed of this diffusion, as a rule, is very high and is limited, first of all, by the speed of blood flow - the blood simply does not have time to carry away dissolved gases. In addition, the process of diffusion is associated with the area through which it occurs and the diameter of the lumen between the resorbing and secretory parts, which, as already mentioned, can be regulated by the sphincter.

Oval capillaries (shown by arrow)

Diversity of the structure of the swim bladder of bony fishes

In conclusion, as I promised, let us return to the diversity of the structure of the swim bladder in different groups of fish. Loss of connection with the intestines, as already mentioned, is not the only trend in the evolution of the swim bladder. From primitive ancient groups to the most modern young taxa, we observe a gradual complication of its structure. This complication lies primarily in the emergence of various zones associated with the performance of certain special functions. The hydrostatic function is provided by two such zones - the red body and oval already described above. Their isolation in different fish can be organized differently, but in general it comes down to the division of the swim bladder into several chambers. As a rule, there are two such chambers - in one the synthesis of gases occurs, and in the other they are absorbed. The diversity of the structure and arrangement of chambers relative to each other in bony fish is very great. Some examples are shown in the figure below.

When describing the swim bladder, the swim bladder of eels of the genera Anguilla and Conger is often mentioned separately (Figure D). Indeed, its structure has a number of interesting features. Having a connection with the intestines, it, however, functions as a closed swim bladder. How does this manifest itself? The fact is that the air channel in eels of these genera is expanded and functionally corresponds to the oval zone - resorption of gases into the blood occurs through its walls, while the synthesis of gases is carried out in a single large elongated chamber equipped with a powerful gas gland. In addition, it is similar to a closed swim bladder due to its blood circulation and the composition of the filling gases.

Speaking about the diversity of the structure of the swim bladder and the peculiarities of its connection with the external environment, one cannot fail to mention the swim bladder of herrings (family Clupeidae). The peculiarities of its structure are associated with the peculiarities of the biology of these fish, which are characterized by significant and sharp vertical migrations. Thus, a typical representative of the herring, the Pacific herring Clupea pallasii, makes similar migrations from the depths of the sea to the surface layers following the plankton on which it feeds. With such movements, the volume of gas in the swim bladder increases sharply due to a decrease in external pressure, which in a normal case could lead to damage to the tissues of the fish (we observe something similar when catching fish from depth - often such catches are accompanied by protrusion of the swim bladder through the mouth of the fish). To prevent this from happening, during the process of evolution, herring acquired an additional hole located in the anal area and connecting the swim bladder with the external environment. Excess air is “bleeded out” through it, and this process can be controlled by the fish itself with the help of the sphincter present here.

I will tell you more about the functioning of the swim bladder in one of the following posts.

Fish are a huge group of vertebrates that live in water. Their main feature is gill breathing. To move in a liquid environment, these animals use a wide variety of devices. The swim bladder is the most important hydrostatic organ that regulates the depth of immersion, and is also involved in breathing and sound generation.

The swim bladder is the most important hydrostatic organ that regulates the diving depth of fish

Development and structure of the hydrostatic organ

The formation of the fish bladder begins at an early stage of development. One of the sections of the rectum, modified into a kind of outgrowth, fills with gas over time. To do this, the fry float up and capture air with their mouths. Over time, the connection between the bladder and the esophagus in some fish is lost.

Fish with an air chamber are divided into two types:

1. Open bladders are able to control filling using a special channel that communicates with the intestines. They can ascend and descend faster, and, if necessary, take air from the atmosphere with their mouths. Most bony fish belong to this type, for example: carp and pike.
2. Closed bladders have a sealed chamber that has no direct communication with the outside world. The gas level is controlled through the circulatory system. The air bladder of fish is entwined with a network of capillaries (red body), which are capable of slowly absorbing or releasing air. Representatives of this type are cod and perch. They cannot afford rapid changes in depth. When instantly removed from the water, such a fish becomes greatly inflated.

The air bladder in fish is a cavity with transparent elastic walls.

According to their structure they are distinguished:

• single-chamber;
• two-chamber;
• three-chamber.

As a rule, most fish have one organ, but in lungfish it is paired. Deep species can get by with a very small bubble.

Functions of the swim bladder

The swim bladder in the body of a fish is a unique and multifunctional organ. It makes life much easier and saves a lot of energy.

The main, but not the only function is the hydrostatic effect. To hover at a certain depth, the density of the body must match the environment. Waterfowl without an air chamber use the constant action of their fins, which leads to unnecessary energy consumption.

The chamber cavity cannot expand and contract arbitrarily. When diving, the pressure on the body increases and it contracts, accordingly the volume of gas decreases, and the overall density increases. The fish easily sinks to the desired depth. When the fish rises to the upper layers of the water, the pressure weakens and the bubble expands like a balloon, pushing the animal upward.

The pressure of the gas on the walls of the chamber generates nerve impulses that cause compensatory movements of the muscles and fins. Using such a system, the fish effortlessly swims at the desired depth, saving up to 70% of energy.

Additional functions:

Such a simple, at first glance, organ is an irreplaceable and vital apparatus.

Fish without an air chamber

From the description of the swim bladder it is clear that how perfect and multifunctional it is. Despite this, some people can easily do without it. The underwater world is home to many animals that do not have a hydrostatic apparatus. They use alternative methods to travel.

Deep-sea species spend their entire lives at the bottom and do not feel the need to rise to the top layer of water. Due to the enormous pressure, the air chamber, even if it existed, would instantly compress and all the air would come out of it. As an alternative, the accumulation of fat is used, which has a density less than that of water and also does not compress.

For fish that need to move very quickly and change depth, a bubble can only do harm. Such representatives of marine fauna (mackerel) use only muscle movements. This increases energy consumption, but also increases mobility.

Cartilaginous fish We are also used to making do on our own. They cannot hover motionless in place. Their skeleton is boneless and therefore has a lower specific gravity. In addition, sharks have a very large liver, two-thirds consisting of fat. Some species can change its percentage, and thereby make their body heavier or lighter.

Aquatic mammals, such as whales and dolphins, are equipped with a thick layer of fatty tissue under the skin and air-filled lungs.

Life on planet Earth originated in the aquatic environment of the world's oceans, and we are all descendants of fish. There are scientific assumptions that in the process of evolution, the respiratory organs of land animals originated from fish bladders.