Swimming bubble in fish: description, function

The fish organism is quite complex and multifunctional. The possibility of staying under water with performing swimming manipulations and maintaining a stable position is conditioned by the special structure of the body. In addition to the habitual even for human organs, in the body of many underwater inhabitants, responsible parts are provided, allowing to ensure buoyancy and stabilization. Essential 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 precursor of human lungs. But in fish, it fulfills its primary tasks, which are not confined to the function of a peculiar balancer.

Formation of a swim bladder

The development of the bladder begins in the larva, from the anterior gut. Most freshwater fish retain this organ throughout life. At the time of release from the larva in the bladder fry, there is still no gaseous composition. To fill it with air, the fish have to rise to the surface and independently grasp the necessary mixture. At the stage of embryonic development the swim bladder forms as a dorsal outgrowth and is under the spine. In the future, the canal that connects this part to the esophagus disappears. But this does not happen to all individuals. On the basis of the presence and absence of this channel, fish are divided into closed- and open-bubble fish. In the first case, airway overgrowth occurs, and gases are discharged through the blood capillaries on the inner walls of the bladder. In open-bladder fish, this organ is connected to the intestine through the air channel, along which the removal of gases takes place.

Gas filling of bubble

Gas glands stabilize the pressure of the bladder. In particular, they contribute to its increase, and if necessary, a red body is involved, formed by a dense capillary network. Since the equalization of pressure in open-bladder fish is slower than in closed-bladder species, they can quickly rise from water depths. When catching specimens of the second type, fishermen are sometimes observed how the swimming bladder protrudes from the mouth. This is due to the fact that the container is inflated in conditions of rapid ascent to the surface from the depth. To such fish, in particular, you can include pike perch, perch and stickleback. Some predators that live on the very bottom have a strongly reduced bladder.

Hydrostatic function

The fish bubble is a multifunctional organ, but its main task is to stabilize the situation under different conditions under water. This is a hydrostatic function, which, incidentally, can be replaced by other parts of the body, which is confirmed by examples of fish that do not have such a bubble. Either way, the main function helps fish to 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 time of active immersion, the body contracts together with the bubble, and when it comes to ascent, on the contrary, it spreads. During the dive, the mass of the displaced volume is reduced and becomes smaller than the weight of the fish. Therefore, the fish can go down without any difficulties. The lower the immersion, the higher the force of pressure becomes and the more the body contracts. Inverse processes occur at the time of ascent - the gas expands, as a result of which the mass is eased and the fish easily rises.

Functions of the senses

Along with the hydrostatic function, this organ acts and in some way a hearing aid. With its help, fish can perceive noise and vibration waves. But this ability is not available to all species - in the category with this ability include carp and catfish. But the sound perception is provided not by the bladder itself, but by a whole group of organs, into which it enters. Special muscles, for example, can provoke vibrations of the walls of the bladder, which causes sensations of vibrations. It is noteworthy that in some species that have such a bubble, there is no hydrostatics completely, but the possibility of perceiving sounds is preserved. This applies mainly to benthic fish, which spend most of their life on the same level under water.

Protective functions

At moments of danger, minnows, for example, can release gas from the bubble and produce specific sounds that are distinguishable by their congeners. At the same time, one should not think that sound formation is primitive and can not be perceived by other inhabitants of the underwater world. The hills were well known to fishermen with rumbling and grunting sounds. Moreover, the swimming bubble, which fish had available, literally terrified the commands of American submarines during the war - so expressive were the sounds produced. Usually such manifestations take place during moments of nervous overexertion of fish. If, in the case of a hydrostatic function, the operation of the bubble occurs under the influence of external pressure, then sound formation arises as a special protective signal formed exclusively by the fish.

Which fish do not have a swim bladder?

This organ is devoid of sailing fish, as well as species that lead a benthonic lifestyle. Virtually all deepwater individuals also dispense with a swim bladder. This is just the case when buoyancy can be provided by alternative methods - in particular, due to fat accumulation and their ability not to contract. Preservation of the stability of the position is also facilitated by a low body density in some fish. But there is another principle of maintaining the hydrostatic function. For example, a swim bladder in a shark is not provided, so it is forced to maintain a sufficient depth of immersion due to active manipulation of the body and fins.

Conclusion

It's no accident that many scientists draw parallels between the human respiratory organs and the fish's bladder. These parts of the body are united by an evolutionary relationship, in the context of which the modern structure of fish should be considered. The fact that the swim bladder is not found in all species of fish, causes its inconsistency. This does not mean that this body is unnecessary, but the processes of its atrophy and reduction testify to the possibility of dispensing with this part. In some cases, fishes are used for the same hydrostatic function, internal fat and lower body density, while in others - fins.