Swim bladder and hydrodynamic features of fish. Why do fish need a swim bladder? Functions of the swim bladder

Fish buoyancy (the ratio of fish body density to water density) can be neutral (0), positive or negative. In most species, buoyancy ranges from +0.03 to -0.03. With positive buoyancy, the fish float up, with neutral buoyancy they float in the water column, with negative buoyancy they sink.

Rice. 10. Swim bladder of cyprinids.

Neutral buoyancy (or hydrostatic balance) in fish is achieved:

1) with the help of a swim bladder;

2) watering the muscles and lightening the skeleton (in deep-sea fish)

3) accumulation of fat (sharks, tuna, mackerels, flounders, gobies, loaches, etc.).

Most fish have a swim bladder. Its occurrence is associated with the appearance of a bone skeleton, which increases the proportion of bony fish. In cartilaginous fish, there is no swim bladder; among bony fish, it is absent in bottom fish (gobies, flounders, lumpfish), deep-sea and some fast-swimming species (tuna, bonito, mackerel). An additional hydrostatic adaptation in these fish is the lifting force, which is formed due to muscular efforts.

The swim bladder is formed as a result of protrusion of the dorsal wall of the esophagus, its main function is hydrostatic. The swim bladder also perceives changes in pressure, is directly related to the organ of hearing, being a resonator and reflector of sound vibrations. In loaches, the swim bladder is covered with a bone capsule, has lost its hydrostatic function, and has acquired the ability to perceive changes in atmospheric pressure. In lungfish and bony ganoids, the swim bladder performs the function of breathing. Some fish are able to make sounds with the help of a swim bladder (cod, hake).

The swim bladder is a relatively large elastic sac that is located under the kidneys. It happens:

1) unpaired (most fish);

2) paired (lungfish and multi-feathered).

In many fish, the swim bladder is single-chamber (salmon), in some species it is two-chamber (cyprinids) or three-chamber (mistake), the chambers communicate with each other. In a number of fishes of the swimming bladder, blind processes extend, connecting it with the inner ear (herring, cod, etc.).

The swim bladder is filled with a mixture of oxygen, nitrogen and carbon dioxide. The ratio of gases in the swim bladder in fish varies and depends on the type of fish, depth of habitat, physiological state, etc. In deep-sea fish, the swim bladder contains significantly more oxygen than in species that live closer to the surface. Fish with a swim bladder are divided into open-bladder and closed-bladder. In open bladder fish, the swim bladder is connected to the esophagus by an air duct. These include - lungfish, multifeathers, cartilaginous and bone ganoids, from bony - herring, carp-like, pike-like. The Atlantic herring, sprat and anchovy have, in addition to the usual air duct, a second duct behind the anus that connects the back of the swim bladder to the outside. In closed bladder fishes, there is no air duct (perch-like, cod-like, mullet-like, etc.). The initial filling of the swim bladder with gases in fish occurs when the larva swallows atmospheric air. So, in carp larvae, this occurs 1–1.5 days after hatching. If this does not happen, the development of the larva is disturbed and it dies. In closed-bladder fish, the swim bladder loses contact with the external environment over time; in open-bladder fish, the air duct persists throughout life. The regulation of the volume of gases in the swim bladder in closed bladder fish occurs using two systems:

1) gas gland (fills the bladder with gases from the blood);

2) oval (absorbs gases from the bladder into the blood).

Gas gland - a system of arterial and venous vessels located in front of the swim bladder. An oval area in the inner shell of the swim bladder with thin walls, surrounded by a muscular sphincter, is located in the back of the bladder. When the sphincter is relaxed, gases from the swim bladder enter the middle layer of its wall, where there are venous capillaries and their diffusion into the blood occurs. The amount of absorbed gases is regulated by changing the size of the oval opening.

When closed bladder fish dive, the volume of gases in their swim bladder decreases, and the fish acquire negative buoyancy, but upon reaching a certain depth they adapt to it by releasing gases into the swim bladder through the gas gland. When the fish rises, when the pressure decreases, the volume of gases in the swim bladder increases, their excess is absorbed through the oval into the blood, and then through the gills it is removed into the water. Open-bladder fish do not have an oval; excess gases are expelled out through the air duct. Most open-bubble fish do not have a gas gland (herring, salmon). The secretion of gases from the blood into the bladder is poorly developed and is carried out with the help of the epithelium located on the inner layer of the bladder. Many open-bladder fish take in air before diving to ensure neutral buoyancy at depth. However, during strong dives, it is not enough, and the swim bladder is filled with gases coming from the blood.

Fish are the most ancient primary aquatic vertebrates. In the process of evolution, the class of fish was formed in the aquatic environment, the characteristic features of the structure of these animals are associated with it. The main type of translational movement is lateral wave-like movements due to contractions of the musculature of the caudal region or the entire body. The pectoral and ventral paired fins perform the function of stabilizers, serve to raise and lower the body, turn, stop, slow, smooth movement, and maintain balance. The unpaired dorsal and caudal fins act like a keel, giving the fish's body stability. There are many mucous glands in the skin of fish. The mucous layer they secrete reduces friction and promotes rapid movement, and also protects the body from pathogens of bacterial and fungal diseases. The organs of the lateral line are well developed.

There are about 22 thousand species of fish living in salt and fresh waters. In addition, about 20,000 extinct species are known. About 1.5 thousand species of fish are found in the waters of Russia.

Class characteristic

The class of fish is characterized by the following features: the presence of jaws, active capture of prey, paired limbs (pectoral and ventral fins), three semicircular canals in the inner ear, two external nostrils, a well-developed brain and unstable body temperature.

Fish are animals adapted to rather monotonous living conditions - an aquatic environment, living in which they differentiated into a large number of species. The morphophysiological features of fish organs are as follows.

body integuments. The body is covered with skin consisting of stratified epithelium and corium. Skin glands are unicellular. Outside, the skin is covered with scales, which is a derivative of the skin itself (corium). The main types of scales are placoid (in shark fish) and bony, characteristic of modern bony fish. Of particular interest is the placoid scale. It is the most primitive in structure; scales of other types and teeth of vertebrates have developed from it. The placoid scale consists of a bone plate lying in the skin and a spike sticking out. Outside, it is covered with enamel, under which there is a substance similar to dentin. Shark teeth are true placoid scales. In all other vertebrates, the teeth are built like placoid scales: enamel on the outside, dentin under it, and inside the cavity, where the connective tissue papilla (pulp) penetrates with a blood vessel and a nerve branch. Bone scales consist of bone plates overlapping each other like tiles. They grow throughout life, forming growth rings on the periphery of the plate.

Skeleton. The vertebral bodies are biconcave (amphicoelous); remnants of the chord are preserved between them.

The brain skull, organs of smell, sight and hearing are placed in the brain skull. The oral cavity of the fish is surrounded by a visceral skull. Gill covers and gill arches are located on the sides of the head.

The skeleton of paired fins consists of belts that serve as a support for the limbs. There are two belts - shoulder and pelvic.

musculature. The muscles of the fish are striated, located segmentally. Segments of a complex shape form groups of muscles in the head, jaws, gill covers, pectoral fins, etc. Translational movement is carried out due to the work of special muscles of the paired fins and the caudal fin. There are muscles that move the eyes, jaws and other organs.

Digestive system. The alimentary canal begins with the oral opening, which leads to the oral cavity. The jaws are equipped with teeth that help capture and hold prey. There is no muscular tongue. Next come the pharynx, esophagus, stomach and intestine, ending in the anus. There is a liver and an underdeveloped pancreas.

Through the pharynx and esophagus, food enters the large stomach, where it begins to be digested under the action of hydrochloric acid and pepsin. Partially digested food enters the small intestine, where the ducts of the pancreas and liver flow. The latter secretes bile, which accumulates in the gallbladder. The complex of digestive enzymes secreted by the pancreas and glands of the intestinal mucosa, together with bile, effectively digests proteins, fats and carbohydrates in the alkaline environment of the intestine. At the beginning of the small intestine, blind processes flow into it, due to which the glandular and absorptive surface of the intestine increases. Undigested residues are excreted into the hindgut and through the anus are removed to the outside.

hydrostatic apparatus. The swim bladder is a hydrostatic apparatus. The bubble was formed from an outgrowth of the intestine; located above the intestines; in cyprinids, catfish, pikes, it is connected by a thin tube to the intestines. The bubble is filled with gas, which includes oxygen, carbon dioxide and nitrogen. The amount of gas can be varied and thus regulate the relative density of the fish's body, allowing it to vary its diving depth. If the volume of the swim bladder does not change, the fish is at the same depth, as if hanging in the water column. When the volume of the bubble increases, the fish rises up. When lowering, the reverse process occurs. The wall of the swim bladder is rich in blood vessels, so it can promote gas exchange (as an additional respiratory organ) in some fish burrowing into the mud. In addition, the swim bladder can act as an acoustic resonator when reproducing various sounds.

Respiratory system. The respiratory organs are represented by the gill apparatus. The gills are located on four gill arches in the form of a row of bright red gill lobes, covered on the outside with numerous (up to 15 or more pieces per 1 mm) very thin folds that increase the relative surface of the gills. Water enters the mouth of the fish, is filtered through the gill slits, washing the gills, and is thrown out from under the gill cover. Gas exchange occurs in numerous gill capillaries, in which blood flows towards the water surrounding the gills. Fish are able to assimilate 46-82% of oxygen dissolved in water. Some fish have additional respiratory organs that allow them to use atmospheric oxygen for breathing. Of particular interest is the use of the swim bladder for air breathing.

Opposite each row of gill filaments are whitish gill rakers, which are of great importance for the nutrition of fish: in some they form a filtering apparatus with an appropriate structure, in others they help to keep prey in the oral cavity.

excretory system It is represented by two dark red ribbon-like kidneys lying below the spinal column almost along the entire body cavity. The kidneys filter waste products from the blood in the form of urine, which passes through the two ureters into the bladder, which opens outward behind the anus. A significant part of the poisonous decay products (ammonia, urea, etc.) is excreted from the body through the gill filaments of fish.

Circulatory system. Fish, like cyclostomes, have one circle of blood circulation. The heart of a fish is two-chambered, consisting of an atrium and a ventricle. Between them is a valve that allows blood to flow in one direction. The vessels through which blood moves to the heart are called veins, from the heart - arteries. Venous blood saturated with carbon dioxide from different organs of fish flows through the veins to the heart, enters the atrium, from it into the ventricle. Thus, in the heart of the fish is only venous blood. From the ventricle, blood is ejected into the abdominal aorta, which splits into 4 pairs of afferent branchial arteries that supply blood to the gills. In the gills, the blood is saturated with oxygen. Oxidized blood in the gill capillaries is collected in 4 pairs of efferent gill arteries, which merge into the dorsal aorta. From it, blood is carried through the arteries throughout the body. In the finest capillaries of tissues and organs, arterial blood gives oxygen to the cells of the body, is saturated with carbon dioxide and again enters the veins.

Nervous system has the form of a hollow tube thickened in front. Its anterior end forms the brain, its cavities are called the ventricles of the brain. There are 10 pairs of nerves coming out of the brain. Each nerve begins with dorsal and ventral roots. The abdominal root transmits motor impulses, the dorsal - sensitive. Each spinal nerve, connecting with the sympathetic trunk, which lies parallel to the spinal cord, forms sympathetic ganglia. The motor fibers of the sympathetic trunks and nerves, together with the motor fibers of the vagus nerve, make up the autonomic nervous system, which innervates all internal organs.

The brain has five divisions: anterior, interstitial, midbrain, cerebellum and medulla oblongata. The centers of different sense organs are located in different parts of the brain: chemical sense (smell, taste) - in the forebrain, vision - in the middle, hearing and touch - in the medulla oblongata, coordination of movement - in the cerebellum. The medulla oblongata passes into the spinal cord. The cavity inside the spinal cord is called the spinal canal.

In the olfactory sacs, the folds of the olfactory epithelium are well developed. The nostril is divided in two by a leathery valve (in a swimming fish, water enters the olfactory sac through the anterior and exits through the posterior nasal opening). The importance of smell and "chemical memory" is especially great in migrating anadromous and semi-anadromous fish.

Taste buds, or taste buds, are located in the mucous membrane of the oral cavity, on the head, antennae, elongated rays of the fins, scattered over the entire surface of the body. Tactile bodies and thermoreceptors are scattered in the superficial layers of the skin. Bony fish are able to distinguish temperature drops of 0.4 °C. Predominantly on the head of the fish, receptors for electromagnetic sensation are concentrated.

Of the sense organs, the lateral line, characteristic only of the inhabitants of the water, is the most developed. Its channels stretch laterally along the body from the head to the caudal fin and communicate with the external environment through numerous holes in the scales. On the head, the canal strongly branches and forms a complex network. The lateral line is a very characteristic sense organ: thanks to it, fish perceive water vibrations, the direction and strength of the current, waves that are reflected from various objects. With the help of this organ, fish navigate in water flows, perceive the direction of movement of prey or a predator, and do not run into solid objects in barely transparent water. Organ of chemical sense - paired sacs.

Two large eyes are on the sides of the head. The lens is round, does not change shape and almost touches the flattened cornea (therefore, the fish are short-sighted and see no further than 10-15 m). In most bony fish, the retina contains rods and cones. This allows them to adapt to changing light conditions. Most bony fish have color vision.

The organ of hearing is represented only by the inner ear, or membranous labyrinth, located on the right and left in the bones of the back of the skull. It is filled with endolymph, in which auditory pebbles - otoliths - are in suspension. Sound orientation is very important for aquatic animals, in particular for fish. The speed of sound propagation in water is almost 4 times greater than in air (and is close to the sound conductivity of fish body tissues). Therefore, even a relatively simple hearing organ allows fish to perceive sound waves.

The organ of balance is anatomically connected with the organ of hearing. Represents three semicircular canals lying in three mutually perpendicular planes.

reproduction. The reproductive organs in males are represented by paired testes, and in females by paired ovaries.

Fish breed in water. Most species lay eggs, fertilization is external, sometimes internal (sharks, rays), in these cases live birth is observed. The development of fertilized eggs lasts from several hours (for sprat, many aquarium fish) to several months (for salmon). The larvae that emerge from the eggs have a remnant of the yolk sac with a supply of nutrients. At first, they are inactive and feed only on these substances, and then they begin to actively feed on various microscopic aquatic organisms. After a few weeks, the larva develops into a scaly and adult fish-like fry.

Many marine and freshwater fish breed and live in the same reservoirs (in particular, carp, crucian carp, tench, silver bream, roach, pike, pike perch, cod, hake, hake, flounder). Some fish live in the sea, but enter rivers for spawning, or vice versa - they constantly live in fresh water bodies, and go to the sea for spawning. These are migratory or semi-migratory fish. In particular, sturgeon (sturgeon, stellate sturgeon, beluga) and salmon (chum salmon, pink salmon, chinook, salmon) spend most of their lives in the sea, and go into rivers for spawning. Their spawning migrations are hundreds and thousands of kilometers long, as are the spawning migrations of the river eel. Adult eels live in rivers and migrate to certain parts of the oceans to spawn. So, living in the rivers of Europe and North Africa, the European eel goes to spawn in the Sargasso Sea. Leaf-shaped larvae emerge from the eggs, not at all like adult eels. The larvae are carried away by the current again to the rivers of Europe, their structure gradually changes, eels enter the rivers already with a snake-like body. Spawning migrations facilitate the meeting of sexually mature individuals and create the most favorable conditions for the development of eggs and larvae.

Spawning in fish occurs at different times of the year: in autumn and winter in salmon, in spring - in pike perch, pike, perch, carp, bream, and in summer - in sturgeons and some cyprinids. Most freshwater fish lay their eggs among aquatic plants in shallow water, sturgeons spawn on rocky ground, salmons bury their eggs in the ground (under pebbles or gravel). The fecundity of fish is on average much higher than the fecundity of terrestrial vertebrates, this is due to the large death of eggs and fry.

Phylogeny. Fish are descended from common ancestors with cyclostomes. The evolution of the latter went along the path of development of a mouth without jaws, a visceral skeleton in the form of a lattice, etc., and the evolution of fish - along the path of development of jaws, gill arches, scales, paired fins, etc.

Systematics. The class of fish is divided into several subclasses:

The structure and reproduction of perch

Perch lives in fresh water bodies of various types - lakes, reservoirs, rivers, flowing ponds. The density of water is greater than the density of air, and its resistance to moving bodies is also higher. Therefore, for mobile aquatic animals, the shape of the body is of great importance. Many fish, including perch, spend most of their time in motion, staying in the water column. They have a streamlined spindle-shaped (or torpedo-shaped) body shape; the pointed head smoothly passes into the body, and the body into a narrowed tail.

The body of the perch is covered with bony scales from above, the posterior edges of which overlap the scales of the next row in a tiled manner. From above, the scales are covered with a thin skin, the glands of which secrete mucus. There are paired (pectoral and ventral) and unpaired (dorsal, caudal and undercaudal) fins. Unpaired fins are supported by strong bony fin rays.

The perch skeleton is bony and consists of the spine, skull and skeleton of the limbs (fins). The ridge is divided into the trunk and tail sections. The spinal column consists of 39-42 vertebrae. Each vertebra consists of a biconcave body and processes. In the intervals between adjacent vertebral bodies, remnants of the notochord have been preserved. From above, each vertebra is adjacent to the upper arch, ending in the upper process. The set of upper arches forms a canal in which the spinal cord lies. From below, the lower arches with lower processes adjoin the caudal vertebrae. In the trunk region, long and thin bone ribs are attached to the vertebrae from the side. The spinal column can bend mainly in the horizontal plane. Numerous bones of the perch skull (as well as other bony fish and all vertebrates) form two sections - the brain and gill-jaw. The medulla consists of the cranium, which contains the brain. The gill-maxillary region includes the bones of the upper and lower jaws, gill and hyoid arches. Four large flat integumentary bones form an operculum that protects the gills from the outside. In the perch, the bones of the shoulder and pelvic girdle are also developed, and the girdle of the pectoral fins is much more developed than the girdle of the ventral fins. Numerous sharp teeth on the jaws and bones of the oral cavity help the perch capture and hold prey; fish fry, aquatic invertebrates, etc.

The female has an unpaired ovary in the body cavity, the male has a pair of long white testes. Reproduction of perch begins at the 2-4th year of life, in the spring, as soon as the ice melts in the reservoirs. At this time, the color of the perch becomes especially bright. Fish gather in flocks in shallow places with a very slow current. Each female lays up to 300 thousand eggs, glued together in the form of a strip 1.5-2 m long, which is attached to aquatic plants. Males secrete seminal fluid - milk, in which there is a mass of mobile spermatozoa that fertilize the eggs.

The meaning of fish

Fish are of great economic importance as a valuable food product. At the expense of fish, a person currently receives up to 40% of animal proteins. A small part of the caught fish is fed to artificially bred fur-bearing animals, preparation of fishmeal for feeding livestock, and fertilizer. There are a lot of proteins, vitamins A and D in the tissues of fish (fish oil, which is obtained from the liver of cod fish and sharks, is especially rich in them). From the waste of cutting and processing fish, technical fish oil is obtained, which is used in leather, soap and other industries.

Over 80% of the fish caught comes from marine fishing, about 5% of the catch is migratory fish, no more than 14% - fishing in fresh water. About 69 million tons of fish are harvested annually in the world. In recent decades, overfishing has led to a sharp reduction in the number of certain species (for example, flounder, herring, etc.). The fish productivity of the oceans and seas is negatively affected by water pollution by oil, mercury compounds, lead, herbicides, insecticides, and a decrease in river flow as a result of the construction of reservoirs on rivers. The regulation of fishery in international waters is carried out on the basis of intergovernmental agreements (for example, on the regulation of salmon fishing in the North Pacific Ocean between the USSR, the USA, Canada and Japan, on the fishing of herring in the North Atlantic Ocean, signed by more than 100 countries in November 1982 . international convention on catching fish on the shelf in the 200-mile zone of continental waters).

In our country, the basis of the marine fishery is cod (cod, haddock, hake, hake, pollock, saffron cod, etc.), fishing for oceanic and Azov-Black Sea herring, Baltic herring, or herring, sprat, or sprats, flounder, halibut, sea bass. Also valuable are anadromous and freshwater salmonids (chum salmon, pink salmon, salmon, taimen, whitefish, omul, etc.). Among freshwater fish, cyprinids (especially bream, as well as carp, crucian carp, vobla), pike perch are of industrial importance.

To preserve the stocks of commercial fish, a lot of work is being done in the following main areas: artificial breeding of valuable anadromous (in particular, sturgeon and salmon) and some freshwater fish (carp, grass carp, bighead and white carp, trout), improving spawning conditions for anadromous and semi-anadromous fish, acclimatization of some commercial fish.

Some types of fish can be a source of poisoning. So, in Central Asia there are several types of marinka, the meat of which can be eaten, but the caviar is poisonous. Most poisonous fish (stingrays, sea dragons, sea ruffs, sea bass) inject poison produced by poisonous glands when they are pricked by fin rays or spikes located at the base of the gill covers, on the tail or at the base of the dorsal fin.

The regulation of river flow, the construction of dams and reservoirs on them, the decrease in river flow as a result of the withdrawal of large volumes of water for irrigation of irrigated lands violated the normal regime of many reservoirs and the conditions for spawning of anadromous and semi-anadromous fish. The industrial production of these fish is sharply reduced, in some places they have disappeared. To preserve fish stocks, fish breeding activities are carried out on a large scale. In the lower reaches of many rivers that flow into the Caspian and Black Seas, the seas of the Arctic and Pacific Oceans, there are more than 100 hatcheries. Caviar and milk are taken from the caught mature sturgeon and salmon fish, they are carefully mixed (the so-called dry method of fertilization, in which almost all eggs are fertilized), then water is added and the fertilized caviar is placed in special incubation apparatus. In these devices, running water contains a sufficient amount of oxygen and has the temperature necessary for the development of eggs. The larvae are first kept in special reservoirs (tanks, pools or ponds), fed and released into natural reservoirs as already grown fry.

Pond fish farming is successfully developing. The main objects of fish farming are carp, grass carp, bighead and white carp, trout, tench, catfish. To increase the number of valuable fish (carp, bream, pike perch, roach, etc.), fish hatcheries created on artificial seas-reservoirs and in the estuarine areas of southern rivers are widely used.

Fish farms grow several artificially bred carp (and other species) for two years in a pond system. In autumn, spawners and young fish that have not reached a commercial size are released into deep (up to 2 m) wintering ponds. In spring, producers are transferred to shallow spawning ponds. After spawning, the spawners are again released into the wintering ponds, and the fry are released into the nursery. Juvenile carps spend the winter in wintering ponds; in spring, one-year-old fish are allowed into large feeding ponds. The water from all the ponds is alternately lowered, the ponds are cleaned and fertilized. In addition to natural feed, fish are fed with compound feed. With such cultivation, carps reach a weight of 300-500 g in the fall of the second year of life, 1.5-2 kg in the fall of the third year, and 2-3 kg in the autumn of the third year. Carps are grown in warm-water ponds at a water temperature of 18-23 °C. Often, yearlings or two-year-old carp are grown in paddy fields flooded with water, in peat quarries, in reservoirs - coolers of power plants.

Trout is grown in cold-water ponds with clean running water and a solid, non-silting bottom in the western regions of Ukraine. Some commercial fish have been successfully acclimatized, in particular, mullet from the Black Sea in the Caspian Sea, pike perch and Sevan trout - in the lake. Issyk-Kul, pink salmon - in the basin of the Barents and White Seas, grass carp, bighead carp and white carp from the Amur basin - in water bodies of the south of the European part of Russia and Central Asia. Herbivorous fish - grass carp, motley and white carp - eat reeds, cattails and other aquatic plants, thus they clean irrigation canals in the south of our country and cooling ponds at thermal power plants.

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 provide buoyancy to fish. The swim bladder can perform hydrostatic, respiratory and sound-producing functions.

In bony fish, it is absent in sailfish, as well as in bottom-dwelling 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. In 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 shown not by bony, but by bony (multiple, having unpaired cellular lungs - the lower outgrowth of the pharynx) and lungfish (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 the 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 in the course of evolution. The main modern large taxa of fish in relation to the presence or absence of a swim bladder and its functions are characterized as follows:

Cyclostomes and cartilaginous - no swim bladder. Coelacanth-like (latimeria) - the swim bladder is reduced. Lung-breathing, multi-feathered - available, respiratory organ. Cartilaginous ganoids (sturgeon-shaped) - available, hydrostatic organ. Bone ganoids - available, respiratory organ. Bony fish - there is, in some it is reduced, a hydrostatic organ, in a small number of species it is a respiratory organ.

Description

In the process of embryonic development of fish, the swim bladder arises as a dorsal outgrowth of the intestinal tube and is located under the spine. In the process of further development, the channel 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-bladder. In open bladder fishes ( physiostome) the swim bladder is connected with the intestines by an air duct throughout life, 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 occluded fish ( physioclists) the air duct overgrows, 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 to 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 body of the fish is squeezed and the faster its fall continues. On the contrary, as you ascend closer to the surface, the gas in the swim bladder expands and reduces the specific gravity of the fish, which pushes the fish further to the surface.

Thus, the main purpose of the swim bladder is to provide zero buoyancy in the zone of normal habitat of the fish, where it does not need to expend energy to maintain the body at this depth. For example,

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

Down or up

When a fish dives into the depths, the water pressure on its body immediately increases, the swim bladder begins to shrink and pushes air out of itself. This happens “automatically”, that is, the fish do not independently control the process. The amount of air inside the body decreases and the fish almost does not have to make an effort to dive to a depth.

When the fish rises, everything happens exactly the opposite. The water pressure on the body subsides and the bubble is gradually filled with gas, if the fish stops, the bubble will be able to effortlessly hold it at the desired depth.

The nerve endings that permeate the swimming organ transmit impulses to the central nervous system, and the fish feels: at what depth it is and what pressure it experiences, 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-bladder and open-bladder. In the former, the bladder fills with gases from the blood and also releases them into the vessels, through a special network of capillaries on a thin wall. In open-bladder fish, the bladder is a separate organ and fills up after the fish swallows atmospheric air.

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

Another function of the bubble

Many ichthyologists will not agree with the statement that fish are “examples” 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.

What fish don't have a bladder?

Not all fish have acquired this useful organ; sailboats, many deep-sea and bottom fish do not have a bladder, and why do they need it if they never try to surface.

The body of fish is quite complex and multifunctional. The ability to stay under water with the performance of swimming manipulations and maintaining a stable position is determined by the special structure of the body. In addition to organs familiar even to humans, the body of many underwater inhabitants provides for critical parts that allow for 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 to 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 foregut. Most freshwater fish retain this organ throughout their lives. At the time of release from the larva, the bubbles of the fry do not yet have a gaseous composition. 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. In the future, the channel that connects this part to the esophagus disappears. But this does not happen in all individuals. On the basis of the presence and absence of this channel, the fish are divided into closed- and open-bladed. In the first case, the air duct becomes overgrown, and gases are removed through the blood capillaries on the inner walls of the bladder. In open bladder fish, this organ is connected to the intestines through an air duct, through which gases are excreted.

Gas bubble filling

Gas glands stabilize bladder pressure. In particular, they contribute to its increase, and if necessary, the red body is activated, formed by a dense capillary network. Since pressure equalization is slower in open-bladder fish than in closed-bladder species, they can quickly rise from the depths of the water. 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 under conditions of rapid rise to the surface from the depth. Such fish, in particular, include zander, perch and stickleback. Some predators that live at the very bottom have a strongly reduced bubble.

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 the 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 moment of active immersion, the body contracts together with the bubble, and, on the contrary, straightens out during the ascent. During the dive, 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 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.

Functions 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 far from all species have this ability - carps 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 is included. Special muscles, for example, can provoke vibrations of the walls of the bubble, 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 formation is of a primitive nature and cannot be perceived by other inhabitants of the underwater world. Croakers are well known to fishermen for their rumbling and grunting sounds. Moreover, the swim bladder, which trigle fish have, literally terrified the crews of American submarines during the war - the sounds made were so expressive. Usually, such manifestations take place at moments of nervous overexertion of the 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 formed exclusively by fish.

What fish do not have a swim bladder?

Sailing fish are deprived of this organ, as well as species that lead a demersal lifestyle. Almost all deep-sea individuals also do without a swim bladder. This is exactly the case when buoyancy can be provided in alternative ways - in particular, thanks to fat accumulations and their ability not to compress. The low density of the body in some fish also contributes to maintaining the stability of the position. But there is another principle of maintaining the hydrostatic function. For example, a shark does not have a swim bladder, so it must maintain a sufficient depth of immersion through active manipulation of the body and fins.

Conclusion

Not without reason, many scientists draw parallels between and 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 causes its inconsistency. 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, and in others - fins.