The swimbladder can perform hydrostatic, respiratory and sound-forming functions. It is absent in sailfish, as well as in bottom-dwelling fishes and in deep-sea fishes. In the latter, buoyancy is provided mainly due to fat due to its incompressibility or due to the lower density of the fish body, such as in ancistrus, golomyanka and drop fish. In the course 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 shown not by bony, but by bony (polypere, having unpaired cellular lungs - the lower outgrowth of the pharynx) and lungs (three modern representatives have a variety 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 the teleosts originated from the upper outgrowth of the esophagus.

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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. During further development the duct 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 bubbles. In open-bubble fish ( physostomy) The swim bladder is connected to the intestines throughout life by an air duct through which gases enter and are removed. Such fish can swallow air and thus control the volume of the swim bladder. Carp, herring, sturgeon and others belong to the open-bubble. In adult closed-bubbly fish ( physicalists) the air duct is 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 sinks below this level, its body, experiencing greater external pressure from the water side, 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 more rapidly its fall continues. On the contrary, when surfacing closer to the surface, the gas in the swim bladder expands and decreases 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 normal habitat of fish, where it does not need to spend energy to maintain the body at this depth. For example, sharks that do not have a swim bladder are forced to maintain their depth of submersion with constant active movement.

It would seem that the answer to this question is obvious: to swim, or rather, to stay at the required depth. The fish bubble is like a natural hydrostatic sensor.

Down or up

When the fish goes deep, the water pressure on its body immediately increases, the swim bladder begins to contract and pushes air out of itself. This happens "automatically", that is, the fish do not control the process on their own. The amount of air inside the body decreases and the fish almost does not have to make any efforts to dive to depth.

When the fish rises up, everything happens exactly the opposite. The pressure of water on the body decreases and the bubble gradually fills with gas, if the fish stops, the bubble will be able to hold it at the desired depth without effort.

The nerve endings that penetrate the swimming organ transmit impulses to the central nervous system, and the fish feels: at what depth it is and what pressure it is experiencing, in connection with which it can adjust its movement.

Where does the gas come from and what kind?

Depending on the type of swim bladder, adult fish are divided into two groups: closed-vesicular and open-vesicular. In the first, the bubble is filled with gases from the blood and gives them also to the vessels, through a special network of capillaries on a thin wall. In open-bubble fish, the bladder is a separate organ and fills after the fish swallows atmospheric air.

As for the gas that fills the bubble, it is mainly oxygen, hydrocarbon and some nitrogen.

Another bubble function

Many ichthyologists will disagree with the statement that fish are "models" of silence, because they can and give special signals to their own kind, converting sound waves from water vibrations, and they do this with the help of a swim bladder.

Which fish don't have a bubble?

Not all fish have acquired this useful organ, in sailfish, many deep-sea and bottom fish there is no bubble, and why do they need it if they never try to float to the surface.

Ministry of Agriculture

Russian Federation

FSBEI HPE "Yaroslavl State Agricultural Academy"

Department of Private Animal Science

Discipline test

FISHERIES

Yaroslavl, 2013

QUESTIONS FOR PERFORMANCE OF CONTROL WORK.

4 . Swimming bladder.

24 . Earthen dams and dams.

49 . Characteristics of compound feed.

Question number 4.

SWIMMING BUBBLE.

An important role in ensuring the movement of fish in the water column is played by a special hydrostatic organ - swimmingbubble... It is a single-chambered or two-chambered organ filled with gases. It is absent in deep-sea fish, as well as in fish that quickly change the depth of swimming (tuna, mackerel). In addition to hydrostatic buoyancy, the swimbladder performs a number of additional functions - an additional respiratory organ, a sound resonator, a sound-producing organ (Privezentsev Yu. A., 2000).

Figure 1 - Organs of water and air respiration in adult fish:

1 - protrusion in the oral cavity, 2 - the supragillary organ, 3, 4, 5 - parts of the swim bladder, 6 - protrusion in the stomach, 7 - the site of oxygen absorption in the intestine, 8 - gills

The swimbladder develops in the fish larva from the anterior intestine and remains in most freshwater fish throughout life. After hatching, the fish larvae do not yet have gas in the swim bladder. To fill it, they have to rise to the water surface and suck in air there.

Depending on the anatomy of the bladder, fish are divided into two large groups: open-bubble(most species) and closed vesicular(perch, cod, mullet, stickleback, etc.). In open vesicles, the swim bladder communicates with the intestines by a duct, which is absent in closed vesicles. Since the equalization of pressure in closed vesicles lasts much longer than in open vesicles, they can only rise slowly from deep water layers. Therefore, in these fish, the fore gut protrudes from the mouth due to the strongly swollen swim bladder if they are cut at a depth and quickly removed to the surface. The most famous closed-bubble species are perch, pike perch and stickleback. In some fish living near the bottom, the swim bladder is strongly reduced or completely absent. Catfish, as a typical representative of benthic fish, has only a poorly formed swim bladder... The sculpin goby, which keeps between stones and under them in streams and rivers, does not have a swim bladder at all. Since he is a poor swimmer, he moves along the bottom with his pectoral fins spread apart (www.fishingural.ru).

Figure 2 - Swim bladder: a) the swim bladder associated with the intestines; b) a swim bladder not connected to the intestine.

In carp fish, the swim bladder is divided into anterior and posterior chambers, which are connected by a narrow and short canal. The wall of the anterior chamber consists of an inner and an outer shell. There is no outer shell in the rear chamber. The inner lining of both chambers is formed by a single layer of squamous epithelium, followed by a thin layer of loose connective tissue, muscle cords, and the vascular layer. Next, there are 2-3 elastic plates. The outer shell of the anterior chamber consists of two layers of dense fibrous (needle-like) connective tissue, which gives it a pearlescent sheen. Outside, both chambers are covered with a serous membrane (Grishchenko L.I., 1999).

In juveniles, the bladder is completely transparent and clean, and becomes cloudy with age; consists of a connective tissue shell. The bubble is filled with various gases, the quantitative ratios of which are different. The filled swim bladder is a hydrostatic apparatus that promotes vertical movement of fish as a result of the movement of gases into the anterior or posterior chamber (with a two-chamber bladder). If the carp is forced to inhale air for a longer time, then the anterior chamber of the swim bladder increases significantly (Koch V., Bank O., Jens G., 1980).

The swimbladder is an organ that is reflexively connected to the muscles of the body and influences the tone and coordinated movement of the muscles. The tension of the gases in the swim bladder creates certain impulses for the behavior of the fish. So, for example, if you fill the swim bladder of a sea bass with an indifferent liquid under high pressure so that the walls of the bladder stretch somewhat, the fish swims at the bottom; if the pressure of the liquid on the wall is lowered, then the fish tends upward due to compensatory movements of the fins. Simultaneously with the compensatory movements of the fins, different in either case, either resorption or secretion of gas in the swim bladder occurs, respectively (Puchkov N.V., 1954).

The swim bladder helps the fish to be 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 expend additional energy to maintain the body at this depth.

The fish is deprived of the ability to arbitrarily inflate or constrict the swim bladder. But on the other hand, there are nerve endings in the walls of the bladder that send signals to the brain when it contracts and expands. The brain, on the basis of this information, sends commands to the executive organs - the muscles, with the help of which the fish moves (www.fishingural.ru).

In some fish, the swim bladder also has other functions. For example, carp have a kind of movable connection between the swim bladder and the labyrinth by means of Weber's bones. The anterior part of the swim bladder of carp is elastic and can expand strongly with changes in atmospheric pressure. These extensions are then given over to the Weberian bones, and from the latter to the labyrinth.

Similar connections are found in catfish and are especially prominent in loaches, in which the entire posterior part of the bladder has been lost, as well as its hydrostatic function; the bladder is enclosed in a bone capsule. From the skin on both sides of the body, channels closed from the outside with a membrane, filled with lymph, stretch and approach the walls of the swim bladder in the place where it is free of the bone capsule. Changes in pressure are transmitted from the skin through the channels and the swim bladder, and from the latter through the Weber apparatus to the labyrinth. Thus, this device is similar to an aneroid barometer, and the function of the swim bladder is primarily to perceive changes in atmospheric pressure.

In most fish, the respiratory function of the bladder does not play a significant role. The amount of oxygen that is available in the swim bladder in ruins and carps, as calculations show, could cover the fish's normal need for this gas only within 4 minutes and, therefore, cannot be of practical importance for respiration. But in some fish, breathing with the help of a swim bladder acquires important role... Such fish include, for example, the dog fish (Umbra crameri), found in Europe in the region of the Danube and Dniester rivers. It is able to inhabit the oxygen-poor water of ditches and swamps. If this fish, which is in ordinary water with plants, is prevented from coming to the surface and deprived of its ability to capture atmospheric air, it dies from suffocation in about a day. Experiments have shown that dog fish in humid air without water can remain alive for up to 9 hours, while in boiled and oxygen-poor water, it dies after 40 minutes if it is prevented from capturing air from the atmosphere. If you allow it to rise to the surface, then the dogfish tolerates the content in boiled water without harm to itself and only more often than usual captures air.

Air respiration is most pronounced in lungfish, which, instead of a swim bladder, have real lungs, very similar in structure to the lungs of amphibians. The lungs of lungs consist of many cells, in the walls of which there are smooth muscles and an abundant network of capillaries. In contrast to the swim bladder, the lungs of lungs (as well as multi-feathers) communicate with the intestine from its ventral side and are supplied with blood from the fourth branchial artery, while the swim bladder of other fish receives blood from the intestinal artery (Puchkov N.V., 1954) ...

Question number 24.

EARTH DAMS AND DAMS.

Dams are erected to contain and raise the water level. They block the channels of rivers, ravines and gullies. There are earthen dams, concrete dams, stone dams, etc. In fish farms, earthen dams are mainly built with or without support for slopes. When designing a dam, the dimensions of its main elements are established: the width of the ridge, the excess of the ridge over the normal retaining level, the slopes of the slopes. The head dam is built of such a height, at which a head pond is formed with a volume of water that guarantees the satisfaction of the needs of the economy with a constant flow of water. The dam site is chosen in the narrowest place of the floodplain with dense waterproof soil, where there is no outlet for springs and springs. The width of the crest of the dam is determined based on the operating conditions of the structure, but not less than 3 m.

Dams are erected during the construction of floodplain ponds. Depending on the purpose, they are contour, water protection and separation. Contour dams embank the territory of the floodplain where fish ponds are located. They are designed to protect ponds from flood waters. Separation dams are arranged between two adjacent ponds. To protect the territory of the fish farm from flooding, water protection dams are being built.

During operation, earthen dams and dams can deform and collapse. In this case, the greatest danger is filtration and wave run-up, as a result of which breakthroughs, landslides and other destruction can occur. In case of strong waves, the slope of the dam from the side of the prevailing winds can collapse and it is additionally protected with special fasteners. Prefabricated and monolithic reinforced concrete slabs and other fasteners are used for fastening the upper slopes of the dams of the head and feeding ponds. Reinforced concrete slabs are laid on the slopes of dams and dams, as a rule, during the construction or reconstruction of ponds. Reed and reed growing in the coastal part of the ponds well protect dams and dams from waves and erosion. The upper part of the upstream slope and downstream slope are usually sown with grasses (Privezentsev Yu. A., Vlasov V.A., 2004).

The dam has two slopes - wet, facing the water, and the opposite - dry. The slope of the slopes depends on the height of the dam and the quality of the soil from which the dam is built. A wet slope is arranged double, and in large dams of head ponds even triple (that is, the base of the slope is 2-3 times its height). For summer categories of ponds, it is better to build a wet slope more gently, since it creates a shallow water zone rich in food organisms for fish, and in wintering ponds, this slope should, on the contrary, be steeper in order to avoid a reduction in the area of ​​the wintering pond. To protect against erosion, the slopes are covered with sod, grasses are sown on them, and in large ponds the wet slope is covered with stone, strengthened with wattle mats, walls made of wattle fence, etc. Planting trees on dams is unacceptable, since the roots destroy the dam, the crown shades the water surface and the leaves pollute the pond. In addition, the trees attract birds and other fish enemies to the ponds.

The service life of hydraulic structures is significantly increased with proper and systematic maintenance of them (moyaribka.ru).

In case of strong wave breaks, the slope of the dam from the side of the prevailing winds is additionally protected with special fasteners. For fastening the upper slopes of the dams of feeding and head ponds, reinforced concrete slabs and twigs are used (Grishchenko L.I., 1999).

The best soil for the construction of dams and dams is loam with a significant admixture of sand. If you use only clay, then it cracks and swells when it freezes and subsequent thawing. In addition, it is easily washed away by heavy rains or spring floods. A dam, built of only one sand, filters the water. Silty soils and chernozems are not suitable, since they are easily eroded and poorly compacted.

The site for a dam or dam must be prepared in advance. To do this, remove the entire vegetation layer (turf), remove stumps, shrubs, trees and their roots. If the soil in this place strongly filters the water, then they dig a trench along the axis of the future dam, deepening to a harder soil. The trench is filled with liquid clay and thoroughly rammed (Fig. 3).

Figure 3 - Construction of a dam with a lock:1 - dam;2 - lock

The sediment of the soil of earthen dams and dams usually makes up 10-15% of the total volume of the embankment, but it can be even more - up to 50% if peat is used. This must be taken into account when planning the height of the structure. The dam should rise above the water level by 0.7-1.0 m, the dams - by 0.3-0.5 m. The crest of the dam should be at least 0.5 m wide. , it is desirable to strengthen them (Privezentsev Yu. A., 2000).

Question number 49.

FEED CHARACTERISTICS.

Compound feed Is a multicomponent mixture of various feed products, compiled according to scientifically grounded recipes to ensure adequate nutrition for animals.

The use of pelleted compound feeds, the improvement of their quality and water resistance are the most important source of reducing feed costs when raising fish and increasing the cost of production.

Compound feed is made for different types fish reared in aquaculture, taking into account their age, weight and method of rearing. When creating compound feed recipes, the norms of the physiological needs of fish for energy, nutrients and biologically active substances are used (Privezentsev Yu. A., Vlasov V. A., 2004).

At present, the following standards have been adopted for the nutritional value and quality of compound feed for fish (Table 1).

Table 1 - The amount of basic nutrients and quality indicators of feed for pond fish,%

Nutrients			Rainbow trout
	underyearlings	marketable fish	underyearlings	marketable fish
Crude protein
Crude fat
Nitrogen-free extractives (BEV)
Cellulose
Energy value, thousand kJ / kg
Iodine number,% iodine, no more
Acid number, mg KOH, no more

In accordance with these requirements, compound feed recipes have been developed for different age groups carp, rainbow trout, channel catfish, bester. According to their purpose, they are divided into starting (for larvae and fry) and production (for older age groups).

Table 2 - Characteristics of compound feed (Privezentsev Yu. A., Vlasov V. A., 2004).

Mass fraction of moisture,%, no more
Mass fraction of crude protein,%, not less: starting compound feed (carp grown in industrial conditions, salmon, channel catfish) for sturgeon compound feed used for pond cultivation: underyearlings, repair material and carp producers marketable two-year-olds, three-year-old carp compound feed for the industrial method of carp growing compound feed for growing valuable fish species
Mass fraction of crude fat for carp and other valuable fish species under the industrial method of rearing,% no added fat with added fat
Mass fraction of carbohydrates,%, no more: starting compound feed for carp grown in industrial conditions starting compound feed for salmon starting compound feed for sturgeon
Mass fraction of fiber,%, no more: starting compound feed for fish day production compound feed for fish production compound feed for underyearlings, replacement young animals and producers production compound feed for commercial two-year and three-year-olds
Mass fraction of calcium for all types of fish,%, no more: starting compound feed production compound feed
Mass fraction of phosphorus,%, no more: starting compound feed for valuable fish species production compound feed for valuable fish species starting compound feed for carp
Water resistance of granules, min. not less
Acid number of compound feed, mg KOH, no more
Shelf life, months, no more: compound feed for carp grown in ponds: with the introduction of an antioxidant no antioxidant compound feed for growing fish in industrial conditions: no added fat with added fat

The requirements for starter feeds differ from the requirements for production feeds with a higher protein content (at least 45%), fat, energy value, as well as a greater balance in amino acid composition, vitamins, microelements and other additives (Table 2). Higher requirements are imposed in feed for fish grown in cages and pools, since fish in them are practically devoid of natural food (Grishchenko L.I., 1999).

Each compound feed recipe is assigned a number. According to the Instructions for the preparation of compound feed for fish, numbers from 110 to 119 are established. However, there are modifications to temporary recipes.

Recently Special attention began to focus on the production of preventive (medicinal) feeds containing natural enterosorbent and new effective domestic probiotics, which, on the one hand, neutralize toxicants, and on the other hand, populate the fish organism with bacteria - antagonists of pathogenic microorganisms, causative agents of many infectious diseases of fish (Yu.A. Privezentsev). , Vlasov V.A., 2004).

The main feeds that are used in the preparation of compound feed for carp are presented in table 3.

Table 3 - Ratio of ingredients in compound feed for carp grown in ponds,% (Vlasov, V.A., Skvortsova, E.G., 2010).

Ingredients	For underyearlings and manufacturers	For two-year-olds
1) Oilcakes and meal (at least 2 types)
2) Cereals: cereals
3) Bran
4) Yeast
5) Animal feed
6) Herbal flour
7) Mineral supplements
8) growth stimulants

Fish compound feed is prepared in the form crumbs(starting), granules different diameters according to the age of the fish, as well pasty... Granulated feed is mainly produced centrally at feed mills, and pasty feed is produced directly at fish farms. For carp fish they use sinking ones, and for salmonids they use floating foods (their water resistance is about 10-20 minutes). The best recipes domestic and foreign fish feed contains up to 9-12 different components, not counting the addition of vitamins, mineral salts, etc. They include animal feed, plant feed, microbiological synthesis products, premixes, enzyme preparations, antioxidants, antibiotics (Grishchenko L.I. ., 1999).

Granulated feed is divided into starting and production... They are made in the form of grains and granules. Krupka is intended for feeding fish from larvae to underyearlings weighing 5 g, granules - for underyearlings, yearlings, two-year-olds, three-year-olds, repair material and producers. Depending on the size, grains and granules are subdivided into 10 groups (Table 4).

Table 4 - Characteristics of fish feed

	Diameter, mm	Fish weight, g
			salmon	sturgeon
	Up to 0.2 (grains)
	0.2-0.4 (grits)
	0.4-0.6 (grits)
	0.6-1.0 (grits)
	1.0-1.5 (grains)
	1.5-2.5 (grits)
	3.2 (granules)
	4.5 (granules)
	6.0 (granules)
	8.0 (granules)

The story about the swim bladder was mainly about its position relative to the intestines in different groups fish, as well as the paths of possible evolution from the primary ventral lung of the ancients fish to the present 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 variety of its structure.

Earlier, 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 the 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-vesicular, while the older ones (with earlier evolutionary origin) there is an open bubbling.

Diagram of the structure of the swim bladder of fish

The transition from open bubbles to closed bubbles took place in evolution through a gradual thinning and lengthening of the air channel and the displacement of the place of its connection with the digestive tract from the pharynx to the posterior parts of the intestine. Thus, in modern open-bubble fish this canal is long and narrow, as, for example, in salmonids, and opens behind the stomach, while in the armored pike Lepisosteus, a representative of one of the ancient groups, it is short and wide and opens into the esophagus. This "forward" position shortens the path to the swim bladder for air swallowed from the surface of the water and provides respiratory function.

How the swim bladder works

First, let's talk about how the swim bladder works 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 also changes. How does the volume of the swim bladder change? The first researchers believed that this was carried out only due to the muscles surrounding the swim bladder, the work of which leads to its compression or expansion, which in turn expels air from the bladder or, on the contrary, forces it inside. However, this is not true - the change in the volume of the swim bladder solely due to the work of the 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 the muscles are used in extreme cases. These structures, depending on the advancement of the taxon, can be expressed to varying degrees, but at the same time, two types of them are always distinguished - a red body and an oval. In fact, these are two zones in the shell 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 vesicular fish, the only transport "channel" for gases during the filling and emptying of the swim bladder.

Now let's take a 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 gaseous 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, be lined with multilayer or unilamellar epithelium.

The red body looks like a dense accumulation of money boxes.

Now I will not dwell on the details of the operation of the entire system, but for a further understanding of the structure of the red body, it should be noted that the ingress 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. For the synthesis of 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 the accumulation 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, for different types fish, a wonderful network, as an integral part of the red body, can be developed to varying degrees, however, if there is, then it is built according to one universal principle. This principle lies in the very close location of the capillaries that bring blood to the secretory cells and carry it back. Parallel (but multidirectional) blood transport takes place along these close arterial and venous capillaries, which provides a complex mechanism for pumping the partial pressure of gases in the capillaries and the very possibility of "pumping" gases into the swim bladder. I will try to talk about this in more detail in a separate post, but for now I suggest just taking a look at the figure below, which shows the microstructure of a wonderful network and the paths of gases in its different parts.

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

The arrows show the direction of gases and blood flow.

Two types of wonderful networking

Speaking about the structure of the wonderful network, one cannot fail to mention that there are two types of organization of parallel inflow and outflow capillaries. The miraculous network can be bipolar when two microcapillary networks are in series, or unipolar when there is only one microcapillary network directly adjacent to the secretory cells. These building options are shown in the figure below. In most fish, the wonderful network is built on a 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 bringing in + 1 outgoing) in a micronetwork can vary in different species from a few to several thousand.

Unipolar and bipolar types of the structure of the wonderful network

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 in the case of the red body, forming a dense network. The structure of this network, however, is much simpler, since the mechanism for the reverse transport of gases from the swim bladder into 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 the capillaries are required. The rate of this diffusion, as a rule, is very high and is limited, first of all, by the rate of blood flow - the blood simply does not have time to carry away the dissolved gases. In addition, the diffusion process 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 an arrow)

Variety of the structure of the swim bladder of teleost fish

In conclusion, as I promised, let's return to the variety of swim bladder structures in different groups of fish. Loss of communication with the gut, 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 appearance of various zones associated with the implementation of certain special functions. The hydrostatic function is provided by two such zones - the red body and the oval already described above. Their isolation from different fish can be organized in different ways, but in general it boils down to dividing the swim bladder into several chambers. As a rule, there are two such chambers - in one there is a synthesis of gases, and in the other they are absorbed. The diversity of the structure and arrangement of chambers relative to each other in teleost fishes is very great. Some examples are shown in the figure below.

The swim bladder is often described separately from the swim bladder of the Anguilla and Conger eels (Figure D). Indeed, in its structure there is a series interesting features... Having a connection with the intestine, it, however, functions as a closed-type swim bladder. How is this manifested? The fact is that the air channel in eels of these genera is expanded and functionally corresponds to the oval zone - gases are resorbed into the blood through its walls, while synthesis gases are carried out in a single large elongated chamber equipped with a powerful gas gland. In addition, the peculiarity of blood circulation and the composition of the filling gases bring it closer to the closed-type swim bladder.

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 herring (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 Pacific herring Clupea pallasii makes similar migrations from the depths of the sea to the surface layers following the plankton it feeds on. With such movements, the volume of gas in the swim bladder increases sharply due to a decrease in external pressure, which in the usual case could lead to damage to the fish tissues (we observe something similar when fishing from a depth - often such captures are accompanied by the bulging of the swim bladder through the fish mouth). To prevent this from happening, in the process of evolution, herring acquired an additional opening located in the anal region and connecting the swim bladder with the external environment. Through it, excess air is "vented", and this process can be controlled by the fish itself with the help of the sphincter available here.

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

The fish organism is quite complex and multifunctional. The ability to stay underwater with swimming manipulations and maintaining a stable position is due to the special structure of the body. In addition to the organs familiar even for humans, critical parts are provided in the body of many underwater inhabitants to ensure buoyancy and stabilization. The swim bladder, which is an extension of the intestine, is essential in this context. According to many scientists, this organ can be considered as the predecessor of the human lungs. But in fish, it performs its primary tasks, which are not limited only to the function of a kind of balancer.

Swim bladder formation

The development of the bladder begins in the larva, from the anterior gut. 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. During embryonic development, the swim bladder forms as a dorsal outgrowth and sits under the spine. Subsequently, the canal that connects this part with the esophagus disappears. But this does not happen in all individuals. On the basis of the presence and absence of this channel, fish are divided into closed- and open-bubble. In the first case, the air duct is overgrown, and gases are removed through the blood capillaries on the inner walls of the bladder. In open-bladded fish, this organ is connected to the intestine through the air duct, through which gases are excreted.

Bubble gas filling

Gas glands stabilize the pressure of the bladder. In particular, they contribute to its increase, and if it is necessary to lower it, the red body, formed by a dense capillary network, is involved. Since the equalization of pressure in open-bubble fish occurs more slowly than in closed-bubble 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 swells in conditions of rapid ascent to the surface from depth. These fish, in particular, include pike perch, perch and stickleback. Some predators that live at the very bottom have a highly 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 bubble. One way or another, the main function is to help the 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 together with the bubble, and on the ascent, on the contrary, straightens out. In the process of immersion, the mass of the displaced volume decreases and becomes less than the weight of the fish. Therefore, the fish can go down without much difficulty. The lower the immersion, the higher the pressure force becomes and the more the body is compressed. The reverse processes occur at the moments of ascent - the gas expands, as a result of which the mass is lightened and the fish easily rises up.

Function of the sense organs

Along with the hydrostatic function, this organ also acts as a kind of hearing aid. With its help, fish can perceive noise and vibration waves. But not all species have such an 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 a whole group of organs into which it enters. Special muscles, for example, can cause the walls of the bladder to vibrate, which causes the sensation of vibrations. It is noteworthy that in some species that have such a bubble, hydrostatics are completely absent, but the ability to perceive sounds is preserved. This applies mainly to those who spend most of their lives at the same level under water.

Protective functions

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

What fish don't have a swim bladder?

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

Conclusion

It is not for nothing that many scientists draw parallels between and the fish bubble. 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 inconsistent. This does not mean at all that this organ is unnecessary, but the processes of its atrophy and reduction indicate the possibility of doing without this part. In some cases, fish use the internal fat and density of the lower body for the same hydrostatic function, while in others they use their fins.