Does the fish have blood? Fish class. circulatory system. excretory system. economic importance of fish and the protection of fish resources. Blood and cardiovascular system

Any species, like cartilaginous fish, has a single structure. In their body there is only one circle of blood circulation. Schematically, the sections of the circulatory system of fish represent the following chain of consecutive components: heart, abdominal aorta, arteries on the gills, dorsal aorta, arteries, capillaries and veins.

It has only two chambers and is not adapted, as in other creatures, to perform the function of separating the flow of blood enriched with oxygen from blood that is not enriched with oxygen. Structurally, the heart consists of four chambers located one behind the other. All these chambers are filled with special venous blood, and each of the departments of the heart has its own name - venous sinus, arterial cone, atrium and ventricle. The sections of the heart are separated from each other by a valve, as a result of which, during the contraction of the heart muscles, blood can only move in one direction - in the direction from the venous sinus to the arterial cone. The circulatory system of fish is arranged in such a way that the blood flow is carried out exclusively in this direction and nothing else.

The role of channels for the distribution of nutrients and oxygen throughout the body of fish is performed by arteries and veins. Arteries carry out the function of transporting blood from the heart, and veins - to the heart. Arteries contain oxygenated (oxygenated) blood, while veins contain less oxygenated (deoxygenated) blood.

Venous blood enters a special venous sinus, after which it is delivered by current to the atrium, ventricle and abdominal aorta. The abdominal aorta is connected to the gills by four pairs of efferent arteries. These arteries split into many capillaries in the region of the gill filaments. It is in the gill capillaries that the process of gas exchange occurs, after which these capillaries merge into the efferent gill arteries. The efferent arteries are part of the dorsal aorta.

Closer to the head, branches of the dorsal aorta pass into the carotid arteries. The circulatory system of fish implies the division of each carotid artery into two channels - internal and external. The internal one is responsible for supplying blood to the brain, and the external one performs the function of blood supply to the visceral part of the skull.

Closer to the back of the body of the fish, the aortic roots merge into a single dorsal aorta. Unpaired and paired arteries branch from it in succession, and the circulatory system of fish in this part supplies blood to the somatic part of the body and important internal organs. The dorsal aorta ends with the caudal artery. All arteries branch into many capillaries, in which the process of changing the composition of the blood takes place. In the capillaries, blood is converted into venous blood.

And its further current is carried out according to the following scheme. In the head region, blood is concentrated in the anterior cardinal veins, and in the lower part of the head it is collected in the jugular veins. The vein passing from the head to the tail is divided into two parts in the back - the left and right renal portal veins. Further, the left portal vein branches, forming a system of capillaries that form the portal system of the kidney located on the left. In most bony species, the circulatory system of fish is arranged in such a way that the right portal system of the kidney is, as a rule, reduced.

From the kidneys, the circulatory system of fish drives blood into the cavity of the posterior cardinal veins. The anterior, posterior, and also cardinal veins on each side of the body merge into the so-called Cuvier ducts. Cuvier's ducts on each side are connected to the venous sinus. As a result, the blood transported by the current from the internal organs enters the portal vein of the liver. In the region of the liver, the portal system branches into many capillaries. After that, the capillaries again merge together and form which is connected to the venous sinus.

Blood, together with lymph and intercellular fluid, makes up the internal environment of the body, that is, the environment in which cells, tissues and organs function. The more stable the environment, the more effective the internal structures of the body, since their functioning is based on biochemical processes controlled by enzyme systems, which, in turn, have a temperature optimum and are very sensitive to changes in pH and the chemical composition of solutions. Control and maintenance of the constancy of the internal environment is the most important function of the nervous and humoral systems.

Homeostasis is provided by many (if not all) physiological systems of the body.

fish - organs of excretion, respiration, digestion, blood circulation, etc. The mechanism for maintaining homeostasis in fish is not as perfect (due to their evolutionary position) as in warm-blooded animals. Therefore, the limits of change in the constants of the internal environment of the body in fish are wider than in warm-blooded animals. It should be emphasized that the blood of fish has significant physical and chemical differences. The total amount of blood in the body in fish is less than in warm-blooded animals. It varies depending on living conditions, physiological state, species, age. The amount of blood in bony fish is on average 2-3% of their body weight. In sedentary fish species, blood is not more than 2%, in active species - up to 5%.

In the total volume of body fluids of fish, blood occupies an insignificant share, which can be seen in the example of lamprey and carp (Table 6.1).

Like other animals, the blood in fish is divided into circulating and deposited. The role of the blood depot in them is performed by the kidneys, liver, spleen, gills and muscles. The distribution of blood in individual organs is not the same. So, for example, in the kidneys, blood makes up 60% of the mass of the organ, in the gills - 57%, in the heart tissue - 30%, in the red muscles - 18%, in the liver - 14%. The proportion of blood as a percentage of the total blood volume in the body of fish is high in the mails and vessels (up to 60%), white muscles (16%), gills (8%), red muscles (6%).

Physico-chemical characteristics of fish blood

The blood of fish has a bright red color, an oily texture to the touch, a salty taste, and a specific smell of fish oil.

The osmotic pressure of the blood of bony freshwater fish is 6 - 7 atm, the freezing point is minus 0.5 "C. The pH of the blood of fish ranges from 7.5 to 7.7 (Table 6.2).

Acid metabolites are the most dangerous. To characterize the protective properties of blood in relation to acid metabolites, an alkaline reservoir (reserve of plasma bicarbonates) is used.

The alkaline reserve of fish blood is estimated by different authors at 5-25 cm/100 ml. To stabilize blood pH in fish, the same buffer mechanisms exist as in higher vertebrates. The most effective buffer system is the hemoglobin system, which accounts for 70-75% of the buffer capacity of the blood. Next in terms of functionality is the carbonate system (20-25%). The carbonate system is activated not only (and possibly not so much) by erythrocyte carbonic anhydrase, but also by carbonic anhydrase of the mucous membrane of the gill apparatus and other specific respiratory organs. The role of the phosphate and buffer systems of plasma proteins is less significant, since the concentration of blood components of which they are composed can vary widely in the same individual (3-5 times).

The osmotic pressure of the blood also has a wide range of fluctuations, so the composition of isotonic solutions for different types of fish is not the same (Table 6.3).

Differences in the ionic composition of blood plasma dictate a special approach to the preparation of physiological solutions for manipulations with blood and other tissues and organs in vitro. The preparation of a saline solution involves the use of a small amount of salts. Its composition, as well as physico-chemical properties, are close to those of sea water (Table 6.4).

Tolerance of fish to changes in the salt composition of the environment largely depends on the capabilities of cell membranes. The elasticity and selective permeability of membranes characterizes the indicator of osmotic resistance of erythrocytes.

The osmotic resistance of fish erythrocytes has a large variability within the class. It also depends on the age, season of the year, the physiological state of the fish. In the teleosts group, it is estimated at an average of 0.3-0.4% NaCl. Such a rigid indicator in warm-blooded animals as the content of proteins in the blood plasma is also subject to significant changes. For fish, a five-fold change in the concentration of plasma proteins (albumins and globulins) is permissible, which is absolutely incompatible with life in birds and mammals.

During favorable periods of life, the content of plasma proteins in the blood of fish is higher than after their starvation, wintering, spawning, and also diseases. So, for example, in trout it averages 6-7%, in carp underyearlings - 2-3%, in older fish - 5-6%. In general, there is an increase in the concentration of plasma proteins with the age of the fish, as well as during the growing season. For example, in a carp at the age of two months it is ] 5%, at the age of one year - 3%, at the age of 30 months - 4% -. and for producers at the end of the feeding period - 5-6%. Gender differences are also possible (0.5-1.0%).

The spectrum of plasma proteins is represented by typical groups, i.e. albumins and globulins, however, as a physiological norm, other proteins are found in fish plasma - hemoglobin, heptoglobin. For example, a group of glycoproteins was isolated from the blood plasma of arctic fish species. playing the role of antifreezes, i.e. substances that prevent the crystallization of cellular and tissue water and the destruction of membranes.

Naturally, with such dynamics of the protein composition of plasma, one can also expect variability in the ratio of albumins and globulins in the blood, for example, during the growth of fish (Table 6.5).

6.5. Ontogenetic changes in the protein spectrum of carp blood serum, %

* fractions: alpha/beta/gamma.

The fractional composition of plasma proteins also changes markedly during the growing season. So, for example, in carp underyearlings, differences in protein content by autumn reach 100% in relation to the moment of planting in nursery ponds (Table 6.6). The content of albumins and beta-globulins in the blood of juvenile carp is directly dependent on water temperature. In addition, hypoxia, poor food supply in water bodies also lead to a decrease in the supply of fish with alpha and beta globulins.

In good conditions, with abundant nutrition, an increase in the concentration of whey protein due to the albumin fraction is noted. Ultimately, the provision of fish with albumins (g / kg of live weight) qualitatively and quantitatively characterizes the nutrition of fish, at least during periods of its intensive growth. According to the provision of the fish organism with albumins, it is possible to make a forecast for the release of underyearlings from the upcoming wintering.

6.6. Protein composition of the blood serum of carp fingerlings depending on the season, %

For example, in the water bodies of the Moscow Region, good results in the cultivation of underyearlings and the maximum yield of yearlings after wintering (80-90%) were noted in fish with a total amount of protein in the blood plasma of about 5% and an albumin content of about 6 g/kg of live weight. Individuals with a protein content in the blood serum of up to 3.5% and an albumin content of 0.4 g/kg of live weight and more often died in the process of growth (yield of underyearlings less than 70%) and more difficult to endure wintering (yield of yearlings less than 50%)

Obviously, fish blood plasma albumins function as a reserve of plastic and energy materials, which is used by the body under conditions of forced starvation. The high availability of albumin and gamma globulins to the body creates favorable conditions for optimizing metabolic processes and guarantees high nonspecific resistance,

Fish blood cells

The morphological picture of fish blood has a bright class and species specificity. Mature erythrocytes in fish are larger than warm-blooded animals, have an oval shape and contain a nucleus (Fig. 6.1 and 6.3). Experts explain the long lifespan of red cells (up to a year) by the presence of a nucleus, since the presence of a nucleus suggests an increased ability of the cell membrane and cytosolic structures to be restored.

At the same time, the presence of a nucleus limits the ability of an erythrocyte to bind oxygen and adsorb various substances on its surface. However, the absence of erythrocytes in the blood of eel larvae, many arctic and antarctic fish indicates that the functions of erythrocytes in fish are duplicated by other structures.

The hemoglobin of fish differs in its physicochemical properties from the hemoglobin of other vertebrates. During crystallization, it gives a specific picture (Fig. 6.2).

The number of erythrocytes in the blood of fish is 5-10 times less than in the blood of mammals. In freshwater bony fish, they are 2 times less than in the blood of marine fish. However, even within one species, multiple changes are possible, which can be caused by environmental factors and the physiological state of the fish.

Analysis of the table. 6.7 shows that wintering of fish has a significant effect on the characteristics of red blood. The total amount of hemoglobin over the winter can decrease by 20%. However, when yearlings are transplanted into feeding ponds, erythropoiesis is so activated that red blood indicators are restored to the autumn level in 10-15 days of feeding. At this time, an increased content of immature forms of all cells can be observed in the blood of fish.

Rice. 6.1. Sturgeon blood cells:

1-hemocytoblast; 2- myeloblast; 3- erythroblast; 4- erythrocytes; 5- lymphocytes; 6- monocyte; 7 - neutrophilic myelocyte; 8-segmented eosinophil; 9 - monoblast; 10 - promyelocyte; 11 - basophilic normoblast; 12 - polychromatophilic normoblast; 13- lymphoblast; 14 - eosinophilic metamyelocyte; 15- stab eosinophil; 16 - profile metamyelopit; 17 - stab ketrofil; 18-segmented neutrophil; 19 - platelets; 20- eosinophilic myelocyte; 21 - cells with vacuolated cytoplasm

The characteristic of red blood depends on environmental factors. The availability of hemoglobin in fish is determined by the temperature of the water. Growing fish in conditions of low oxygen content is accompanied by an increase in the total volume of blood, plasma, which increases the efficiency of gas exchange.

A characteristic feature of fish is the polymorphism of reds - the simultaneous presence in the bloodstream of erythrocyte cells of various degrees of maturity (Table 6.8).

An increase in the number of immature forms of erythrocytes is associated with a seasonal increase in metabolism, blood loss, as well as age and sex characteristics of fish. Thus, in spawners, a 2-3-fold increase in immature erythrocytes is observed as the gonads mature, reaching 15% in males before spawning. In the evolution of fish red blood cells, three stages are distinguished, each of which is characterized by the formation of morphologically quite independent cells - erythroblast, normoblasts, and the erythrocyte itself.

The erythroblast is the most immature cell of the erythroid series. Fish erythroblasts can be attributed to medium and large blood cells, since their size ranges from 9 to 14 microns. The nucleus of these cells has a red-violet color (in a smear). Chromatin is evenly distributed throughout the nucleus, forming a mesh structure. At high magnification, from 2 to 4 nucleoli can be found in the nucleus. The cytoplasm of these cells is strongly basophilic. It forms a relatively regular ring around the nucleus.

Basophilic normoblast is formed from erythroblast. This cell has a denser, smaller nucleus that occupies the central part of the cell. The cytoplasm is characterized by mild basophilic properties. The polychromatophilic normoblast is distinguished by an even smaller nucleus with sharply defined edges, which is somewhat displaced from the center of the cell. Another feature is that the nuclear chromatin is located radially, forming fairly regular sectors within the nucleus. The cytoplasm of the cells in the smear is not basophilic, but dirty pink (light lilac) staining.

Rice. 6.2. Fish hemoglobin crystals

The oxyphilic normoblast has a rounded shape with a centrally located rounded and dense nucleus. The cytoplasm is located in a wide ring around the nucleus and has a well-defined pink color.

Fish erythrocytes complete the erythroid series. They have an oval shape with a dense core of red-violet color repeating their shape. Chromatin forms clusters in the form of specific clumps. In general, a mature erythrocyte is similar to an oxyphilic normoblast both in the nature of the staining of the nucleus and cytoplasm in the smear, and in the microstructure of the protoplasm. It is distinguished only by an elongated shape. The erythrocyte sedimentation rate (ESR) in fish is normally 2-10 mm/h. White blood cells (leukocytes). Fish blood leukocytes are present in greater numbers than those of mammals. Fish are characterized by a lymphocytic profile, i.e. more than 90% of white cells are lymphocytes (Tables 6.9, 6.10).

6.9. The number of leukocytes in 1 mm

Phagocytic forms are monocytes and polymorphonuclear cells. Throughout the life cycle, the leukocyte formula changes under the influence of environmental factors. During spawning, the number of lymphocytes decreases in favor of monocytes and polymorphonuclear cells.

The blood of fish contains polymorphonuclear cells (granulocytes) at different stages of maturity. The ancestor of all granulocytes should be considered myeloblast (Fig. 6.3).

Rice. 6.3. Carp blood cells:

1 - hemocytoblast; 2- myeloblast; 3 - erythroblast; 4-erythrocytes; 5 - lymphocytes; 6- monocyte; 7 - neutrophilic myelocyte; 8- pseudoeosinophilic myelocyte; 9 - monoblast; 10 - promyelocyte; 11 - basophilic normoblast; 12 - polychromatophilic normoblast; 13 - lymphoblast; 14 - neutrophilic metamyeloiitis; 15 - pseudoeosinophilic metamyelocyte; 16 - stab neutrophil; 17 - segmented neutrophil; 18- pseudobasophil; 19- platelet This cell is distinguished by its large size and a large red-violet nucleus, which occupies most of it. The size of myeloblasts range from 12 to 20 microns. The microstructure of cells is characterized by an abundance of ribosomes, mitochondria, as well as the intensive development of the Golgi complex. At maturation, the myeloblast becomes a promyelocyte.

The promyelocyte retains the size of its predecessor, i.e. is a large cell. Compared with myeloblast, the promyelocyte has a denser red-violet nucleus with 2-4 nucleoli and a weakly basophilic granular cytoplasm. In addition, there are fewer ribosomes in this cell. The myelocyte is smaller than the previous cells (10-15 microns). The dense round nucleus loses its nucleoli. The cytoplasm occupies a larger volume, has a pronounced granularity, which is detected by acidic, neutral and basic dyes.

The metamyelocyte is distinguished by an elongated nucleus with spotted chromatin. The cytoplasm of cells has a heterogeneous granular structure. The stab granulocyte represents a further stage in the evolution of granuloids. Its distinguishing feature is the shape of a dense core. It is elongated, with a mandatory interception. In addition, the nucleus occupies a smaller part of the cell volume.

The segmented granulocyte represents the final stage of myeloblast maturation, i.e. is the most mature cell of the granular series of fish blood. Its distinguishing feature is the segmented nucleus. depending

depending on the color of the cytoplasmic granules, segmented cells are additionally classified into neutrophils, eosinophils, basophils, as well as pseudoeosinophils and pseudobasophils. Some researchers deny the presence of basophilic forms of granulocytes in sturgeons.

Cell polymorphism is also noted in fish blood lymphocytes. The least mature cell of the lymphoid series is the lymphoblast, which is formed from the hemocytoblast.

The lymphoblast is distinguished by a large rounded red-violet nucleus with a reticulated chromatin structure. The cytoplasm accounts for a narrow strip stained with basic dyes. When studying a cell under high magnification, many ribosomes and mitochondria are found against the background of a weak development of the Golgi complex and the endoplasmic reticulum. A prolymphocyte is an intermediate stage in the development of lymphoid cells. The prolymphocyte differs from its predecessor in the structure of chromatin in the nucleus: it loses its mesh structure.

The lymphocyte has a red-violet nucleus of various shapes (round, oval, rod-shaped, lobed), which is located asymmetrically in the cell. Chromatin is distributed unevenly within the nucleus. Therefore, cloud-like structures are visible on stained preparations within the nucleus. The cytoplasm is located asymmetrically relative to the nucleus and often forms pseudopodia, which gives the cell an amoeboid shape.

Fish lymphocyte is a small cell (5-10 microns). When microscopy of blood smears, lymphocytes can be confused with other small blood cells - platelets. When recognizing them, one should take into account the differences in the shape of the cells, the nucleus, and the boundaries of the distribution of the cytoplasm around the nucleus. In addition, the color of the cytoplasm in these cells is not the same: in lymphocytes it is blue, in platelets it is pink. In turn, blood lymphocytes are a heterogeneous group of cells that differ in morphofunctional characteristics. Here it is enough to mention that T- and B-lymphocytes are secreted, which have a different origin and their own unique functions in the reactions of cellular and humoral immunity.

The monocytoid series of fish white blood is represented by at least three types of rather large (11 - 17 microns) cells.

The monoblast is the least mature cell of this series. It is distinguished by a large red-violet nucleus of irregular shape: bean-shaped, horseshoe-shaped, sickle-shaped. The cells have a wide layer of cytoplasm with weakly basophilic properties.

A promonocyte differs from a monoblast by a looser nuclear structure and smoky chromatin (after staining). The cytoplasm of these cells is also unevenly stained, which makes it hazy.

Monocyte is the most mature cell of the series. It has a large red-violet nucleus with a relatively small amount of chromatin substance. The shape of the nucleus is often irregular. On stained preparations, the cytoplasm retains haze. Deterioration of fish keeping conditions (hypoxia, bacterial and chemical pollution of the reservoir, starvation) leads to an increase in phagocytic forms. During the wintering of carp, a 2-16-fold increase in the number of monocytes and polymorphonuclear cells is noted, with a simultaneous decrease by 10-30% in the number of lymphocytes. Thus, the indicators of fish grown in good conditions should be taken as the physiological norm. Fish blood platelets. There is no more conflicting information about the morphology and origin of blood cells than information about fish platelets. Some authors deny the existence of these cells altogether. However, the point of view about the great morphological diversity and high variability of platelets in the body of fish looks more convincing. Not the last place in this dispute is occupied by the features of methodological techniques in the study of platelets.

In blood smears made without the use of anticoagulants, many researchers find at least four morphological forms of platelets - styloid, spindle-shaped, oval and round. Oval platelets are outwardly almost indistinguishable from small lymphocytes. Therefore, when counting platelets in a blood smear, their quantitative characteristic of 4% is probably underestimated when using this technique.

More advanced methods, such as immunofluorescence with blood stabilization with heparin, made it possible to determine the ratio of lymphocytes: platelets as 1: 3. The concentration of platelets in 1 mm3 was 360,000 cells. The question of the origin of platelets in fish remains open. The widespread point of view about the common origin with lymphocytes from small lymphoid hemoblasts has recently been questioned. Platelet-producing tissue has not been described in fish. However, it is noteworthy that in the prints from the spleen sections, a large number of oval cells are almost always found, strongly resembling the oval forms of platelets. Therefore, there is reason to believe that fish platelets are formed in the spleen.

Thus, one can definitely speak about the de facto existence of platelets in the class of fish, while noting their great morphological and functional diversity.

The quantitative characteristic of this group of cells does not differ from that of other classes of animals.

There is a common point of view among fish blood researchers regarding the functional significance of platelets. Like platelets of other classes of animals in fish, they carry out the process of blood clotting. In fish, the blood clotting time is a rather unstable indicator, which depends not only on the method of taking blood, but also on environmental factors, the physiological state of the fish (Table 6.11).

Stress factors increase the rate of blood clotting in fish, which indicates a significant influence of the central nervous system on this process (Table 6.12).

6.12. Effect of stress on blood clotting time in trout, s

Table data. 6.12 indicate that the reaction of adaptation in fish includes a mechanism for protecting the body from blood loss. The first stage of blood coagulation, i.e. the formation of thromboplastin, is controlled by the hypothalamic-pituitary system and adrenaline. Cortisol probably does not affect this process. The literature also describes interspecies differences in blood coagulation in fish (Table 6.13). However, these data should be treated with some skepticism, keeping in mind that caught fish are fish that have been severely stressed. Therefore, the interspecies differences described in the specialized literature may well be the result of different stress resistance in fish.

Thus, the body of fish is reliably protected from large blood loss. The dependence of fish blood clotting time on the state of the nervous system is an additional protective factor, since large blood loss is most likely to occur in stressful situations (predator attacks, fights).

Heart. Fish, like Cyclostomata, have (Fig. 96) a heart, which is a particularly developed part of the longitudinal abdominal vessel. Its task is to suck up the venous blood brought by the veins from various parts of the body, and push this venous blood forward and up to the gills. The heart of fish is thus a venous heart. In accordance with its function, the heart is located immediately behind the gills and in front of the place where the veins that bring blood from different parts of the body flow into the abdominal vessel. The heart is placed in a special cavity, the so-called pericardial cavity, which in Selachia and Chondrosteoidci is also connected to the common body cavity, of which it is a part.

The cardiovascular system of fish consists of the following elements:

Circulatory system, lymphatic system and hematopoietic organs.

The circulatory system of fish differs from other vertebrates in one circle of blood circulation and a two-chambered heart filled with venous blood (with the exception of lungfish and crossopterans). The main elements are: Heart, blood vessels, blood (Fig. 1b

Figure 1. The circulatory system of fish.

Heart in fish is located near the gills; and is enclosed in a small pericardial cavity, and in lampreys - in a cartilaginous capsule. The fish heart is two-chambered and consists of a thin-walled atrium and a thick-walled muscular ventricle. In addition, adnexal sections are also characteristic of fish: the venous sinus, or venous sinus, and the arterial cone.

The venous sinus is a small thin-walled sac in which venous blood accumulates. From the venous sinus, it enters the atrium, and then into the ventricle. All openings between the sections of the heart are equipped with valves, which prevents the backflow of blood.

In many fish, with the exception of teleosts, an arterial cone adjoins the ventricle, which is part of the heart. Its wall is also formed by cardiac muscles, and on the inner surface there is a system of valves.

In bony fish, instead of an arterial cone, there is an aortic bulb - a small white formation, which is an expanded part of the abdominal aorta. Unlike the arterial cone, the aortic bulb consists of smooth muscles and has no valves (Fig. 2).

Fig.2. Scheme of the circulatory system of a shark and the structure of the heart of a shark (I) and bony fish (II).

1 - atrium; 2 - ventricle; 3 - arterial cone; 4 - abdominal aorta;

5 - afferent gill artery; 6 - efferent gill artery; 7- carotid artery; 8 - dorsal aorta; 9 - renal artery; 10 - subclavian artery; I - tail artery; 12 - venous sinus; 13 - Cuvier duct; 14 - anterior cardinal vein; 15 - tail vein; 16 - the portal system of the kidneys; 17 - posterior cardinal vein; 18 - lateral vein; 19 - subintestinal vein; 20-portal vein of the liver; 21 - hepatic vein; 22 - subclavian vein; 23 - aortic bulb.

In lungfish, due to the development of pulmonary respiration, the structure of the heart has become more complicated. The atrium is almost completely divided into two parts by a septum hanging from above, which continues in the form of a fold into the ventricle and arterial cone. Arterial blood from the lungs enters the left side, venous blood from the venous sinus enters the right side, so more arterial blood flows in the left side of the heart, and more venous blood flows in the right side.

Fish have a small heart. Its mass in different fish species is not the same and ranges from 0.1 (carp) to 2.5% (flying fish) of body weight.

The heart of cyclostomes and fish (with the exception of lungfish) contains only venous blood. The heart rate is specific for each species, and also depends on the age, physiological state of the fish, water temperature and is approximately equal to the frequency of respiratory movements. In adult fish, the heart contracts rather slowly - 20-35 times per minute, and in juveniles much more often (for example, in sturgeon fry - up to 142 times per minute). When the temperature rises, the heart rate increases, and when it decreases, it decreases. In many fish during the wintering period (bream, carp), the heart contracts only 1-2 times per minute.

The circulatory system of fish is closed. The vessels that carry blood away from the heart are called arteries, although venous blood flows in some of them (abdominal aorta, bringing gill arteries), and the vessels that bring blood to the heart - veins. Fish (except lungfish) have only one circle of blood circulation.

In bony fish, venous blood from the heart through the aortic bulb enters the abdominal aorta, and from it through the afferent branchial arteries to the gills. The teleosts are characterized by four pairs of afferent and as many efferent gill arteries. Arterial blood through the efferent branchial arteries enters the paired supra-gill vessels, or roots of the dorsal aorta, passing along the bottom of the skull and closing in front, forming a head circle, from which vessels depart to different parts of the head. At the level of the last branchial arch, the roots of the dorsal aorta, merging together, form the dorsal aorta, which runs in the trunk region under the spine, and in the caudal region in the hemal canal of the spine and is called the caudal artery. The arteries that supply arterial blood to organs, muscles, and skin are separated from the dorsal aorta. All arteries break up into a network of capillaries, through the walls of which there is an exchange of substances between blood and tissues. Blood is collected from the capillaries into the veins (Fig. 3).

The main venous vessels are the anterior and posterior cardinal veins, which, merging at the level of the heart, form transversely running vessels - the Cuvier ducts, which flow into the venous sinus of the heart. The anterior cardinal veins carry blood from the top of the head. From the lower part of the head, mainly from the visceral apparatus, blood is collected in the unpaired jugular (jugular) vein, which stretches under the abdominal aorta and near the heart is divided into two vessels that independently flow into the Cuvier ducts.

From the caudal region, venous blood is collected in the caudal vein, which passes in the hemal canal of the spine under the caudal artery. At the level of the posterior edge of the kidneys, the tail vein divides into two portal veins of the kidneys, which stretch along the dorsal side of the kidneys for some distance, and then branch into a network of capillaries in the kidneys, forming the portal system of the kidneys. The venous vessels leaving the kidneys are called the posterior cardinal veins, which run along the underside of the kidneys to the heart.

On their way, they receive veins from the reproductive organs, the walls of the body. At the level of the posterior end of the heart, the posterior cardinal veins merge with the anterior ones, forming paired Cuvier ducts, which carry blood into the venous sinus.

From the digestive tract, digestive glands, spleen, swim bladder, blood is collected in the portal vein of the liver, which, after entering the liver, branches into a network of capillaries, forming the portal system of the liver. From here, blood flows through the paired hepatic veins into the venous sinus. Therefore, fish have two portal systems - the kidneys and the liver. However, the structure of the portal system of the kidneys and the posterior cardinal veins in bony fish is not the same. So, in some cyprinids, pike, perch, cod, the right portal system of the kidneys is underdeveloped and only a small part of the blood passes through the portal system.

Due to the great diversity of the structure and living conditions of various groups of fish, they are characterized by significant deviations from the outlined scheme.

Cyclostomes have seven afferent and as many efferent gill arteries. The supragillary vessel is unpaired, there are no aortic roots. The portal system of the kidneys and the Cuvier ducts are absent. One hepatic vein. There is no inferior jugular vein.

Cartilaginous fish have five afferent gill arteries and ten efferent ones. There are subclavian arteries and veins that provide blood supply to the pectoral fins and shoulder girdle, as well as lateral veins starting from the ventral fins. They pass along the side walls of the abdominal cavity and merge with the subclavian veins in the region of the shoulder girdle.

The posterior cardinal veins at the level of the pectoral fins form extensions - the cardinal sinuses.

In lungfish, more arterial blood, concentrated in the left side of the heart, enters the two anterior branchial arteries, from which it is sent to the head and dorsal aorta. More venous blood from the right side of the heart passes into the two posterior branchial arteries and then into the lungs. During air breathing, the blood in the lungs is enriched with oxygen and enters the left side of the heart through the pulmonary veins (Fig. 4).

In addition to the pulmonary veins, lungfish have abdominal and large cutaneous veins, and instead of the right cardinal vein, the posterior vena cava is formed.

Lymphatic system. The lymphatic system, which is of great importance in metabolism, is closely connected with the circulatory system. Unlike the circulatory system, it is open. Lymph is similar in composition to blood plasma. During the circulation of blood through the blood capillaries, part of the plasma containing oxygen and nutrients leaves the capillaries, forming tissue fluid that bathes the cells. Part of the tissue fluid containing metabolic products re-enters the blood capillaries, and the other part enters the lymphatic capillaries and is called lymph. It is colorless and contains only lymphocytes from the blood cells.

The lymphatic system consists of lymphatic capillaries, which then pass into the lymphatic vessels and larger trunks, through which the lymph slowly moves in one direction - to the heart. Consequently, the lymphatic system carries out the outflow of tissue fluid, complementing the function of the venous system.

The largest lymphatic trunks in fish are paired subvertebrals, which stretch along the sides of the dorsal aorta from tail to head, and lateral, which pass under the skin along the lateral line. Through these and head trunks, lymph flows into the posterior cardinal veins at the Cuvier ducts.

In addition, fish have several unpaired lymphatic vessels: dorsal, ventral, spinal. There are no lymph nodes in fish, however, in some species of fish, under the last vertebrae, there are pulsating paired lymphatic hearts in the form of small oval pink bodies that push lymph to the heart. The movement of the lymph is also facilitated by the work of the trunk muscles and respiratory movements. Cartilaginous fish do not have lymphatic hearts and lateral lymphatic trunks. In cyclostomes, the lymphatic system is separate from the circulatory system.

Blood. The functions of the blood are diverse. It carries nutrients and oxygen throughout the body, frees it from metabolic products, connects the endocrine glands with the relevant organs, and also protects the body from harmful substances and microorganisms. The amount of blood in fish ranges from 1.5 (stingray) to 7.3% (scad) of the total mass of fish, while in mammals it is about 7.7%.

Rice. 5. Fish blood cells.

Fish blood consists of blood fluid, or plasma, formed elements - red - erythrocytes and white - leukocytes, as well as platelets - platelets (Fig. 5). Compared to mammals, fish have a more complex morphological structure of blood, since in addition to specialized organs, the walls of blood vessels also participate in hematopoiesis. Therefore, there are shaped elements in the bloodstream at all phases of their development. Erythrocytes are ellipsoidal and contain a nucleus. Their number in different fish species ranges from 90 thousand / mm 3 (shark) to 4 million / mm 3 (bonito) and varies in the same species B: depending on the sex, age of the fish, as well as environmental conditions.

Most fish have red blood, which is due to the presence of hemoglobin in red blood cells, which carries oxygen from the respiratory system to all cells of the body.

Rice. 6. Antarctic whitefish

However, in some Antarctic whitefish, which include icefish, the blood contains almost no red blood cells, and therefore hemoglobin or any other respiratory pigment. The blood and gills of these fish are colorless (Fig. 6). In conditions of low water temperature and high oxygen content in it, respiration in this case is carried out by diffusion of oxygen into the blood plasma through the capillaries of the skin and gills. These fish are inactive, and their lack of hemoglobin is compensated by the increased work of a large heart and the entire circulatory system.

The main function of leukocytes is to protect the body from harmful substances and microorganisms. The number of leukocytes in fish is high, but variable

in and depends on the species, gender, physiological state of the fish, as well as the presence of a disease in it, etc.

A sculpin bull, for example, has about 30 thousand / mm 3, a ruff has from 75 to 325 thousand / mm 3 leukocytes, while in humans there are only 6-8 thousand / mm 3. A large number of leukocytes in fish indicates a higher protective function of their blood.

Leukocytes are divided into granular (granulocytes) and non-granular (agranulocytes). In mammals, granular leukocytes are represented by neutrophils, eosinophils, and basophils, while non-granular leukocytes are represented by lymphocytes and monocytes. There is no generally accepted classification of leukocytes in fish. The blood of sturgeons and teleosts differs primarily in the composition of granular leukocytes. In sturgeon they are represented by neutrophils and eosinophils, while in teleosts they are represented by neutrophils, pseudoeosinophils and pseudobasophils.

Non-granular fish leukocytes are represented by lymphocytes and monocytes.

One of the features of the blood of fish is that the leukocyte formula in them, depending on the physiological state of the fish, varies greatly, therefore not all granulocytes characteristic of this species are always found in the blood.

Platelets in fish are numerous, and larger than in mammals, with a nucleus. They are important in blood clotting, which is facilitated by the mucus of the skin.

Thus, the blood of fish is characterized by signs of primitiveness: the presence of a nucleus in erythrocytes and platelets, a relatively small number of erythrocytes, and a low content of hemoglobin, which cause a low metabolism. At the same time, it is also characterized by features of high specialization: a huge number of leukocytes and platelets.

Hematopoietic organs. If in adult mammals hematopoiesis occurs in the red bone marrow, lymph nodes, spleen and thymus, then in fish that do not have either bone marrow or lymph nodes, various specialized organs and foci participate in hematopoiesis. So, in sturgeons, hematopoiesis mainly occurs in the so-called lymphoid organ located in the head cartilages above the medulla oblongata and cerebellum. All types of shaped elements are formed here. In bony fish, the main hematopoietic organ is located in the recesses of the outer part of the occipital region of the skull.

In addition, hematopoiesis in fish occurs in various foci - the head kidney, spleen, thymus, gill apparatus, intestinal mucosa, walls of blood vessels, as well as in the pericardium of teleosts and the endocardium of sturgeons.

head kidney in fish, it is not separated from the trunk and consists of lymphoid tissue, in which erythrocytes and lymphocytes are formed.

Spleen fish have a variety of shapes and locations. Lampreys do not have a formed spleen, and its tissue lies in the sheath of the spiral valve. In most fish, the spleen is a separate dark red organ located behind the stomach in the folds of the mesentery. In the spleen, red blood cells, white blood cells and platelets are formed, and the destruction of dead red blood cells occurs. In addition, the spleen performs a protective function (phagocytosis of leukocytes) and is a blood depot.

thymus(goiter, or thymus, gland) is located in the gill cavity. It distinguishes the surface layer, cortical and cerebral. Here lymphocytes are formed. In addition, the thymus stimulates their formation in other organs. Thymus lymphocytes are capable of producing antibodies involved in the development of immunity. It reacts very sensitively to changes in the external and internal environment, responding by increasing or decreasing its volume. The thymus is a kind of guardian of the body, which, under adverse conditions, mobilizes its defenses. It reaches its maximum development in fish of younger age groups, and after they reach sexual maturity, its volume noticeably decreases.

Blood. The main functions of the blood are:

1) transport (carries nutrients, oxygen, metabolic products, endocrine glands, etc.);

2) protective (protects against harmful substances and microorganisms).

The amount of blood in cyclostomes ranges from 4 to 5% of the total body weight, in fish - from 1.5 (stingray) to 7.3% (scad).

Fish blood is made up of:

1) plasma (or blood fluid);

2) formed elements: erythrocytes (red), leukocytes (white) and platelets (platelets).

Fish, compared to mammals, have a more complex morphological structure of blood; in the bloodstream, fish have formed elements at all phases of their development, since along with specialized organs, the walls of blood vessels also participate in hematopoiesis.

Fish erythrocytes are ellipsoidal in shape and contain a nucleus. Their number depends on the sex, age of the fish, environmental conditions and ranges from 90 thousand / mm 3 (shark) to 4 million / mm 3 (bonito). Red blood cells contain hemoglobin (respiratory pigment) that carries oxygen from the respiratory system to all cells in the body. The content of hemoglobin in the blood of fish depends on their mobility, in fast-swimming species it is higher. The content of hemoglobin in the blood of stingrays ranges from 0.84.5 g%, sharks - 3.4-6.5 g%, bony fish - 1.1-17.4 g%. Most fish have red blood, in some Antarctic species the blood and gills are colorless, the blood contains almost no red blood cells (icefish). Under conditions of low water temperature and high oxygen content in it, the respiration of these fish species is carried out by diffusion of oxygen into the blood plasma through the capillaries of the skin and gills. These are sedentary fish and the lack of hemoglobin in them is compensated by the increased work of a large heart and the entire circulatory system.

Leukocytes protect the body of fish from harmful substances and microorganisms. Their number in fish is large and depends on the species, sex, physiological state, the presence of diseases, etc. In ruff, they number from 75 to 325 thousand / mm 3 (in humans, they are 6-8 thousand / mm 3). A large number of leukocytes in fish indicates a high protective function of the blood.

Leukocytes are divided into:

1) granular (granulocytes);

2) non-granular (agranulocytes).

There is no generally accepted classification of leukocytes in fish.

Platelets are relatively large cells with a nucleus; they are numerous in fish and are involved in blood clotting.

Thus, the blood of fish is characterized by:

the presence of a nucleus in erythrocytes and platelets;

a relatively small number of red blood cells and a low content of hemoglobin;

a large number of leukocytes and platelets.

The first two signs speak of the primitiveness of the circulatory system of fish, the third - of its high specialization.

Hematopoietic organs. Various specialized organs and areas are involved in the hematopoiesis of fish. In sturgeons, hematopoiesis mainly occurs in the lymphoid organ, which is located under the roof of the skull, in bony fish - behind the skull, in front of the kidneys (all types of blood cells are formed here).

Hematopoietic organs in fish are also:

1) head kidney;

2) spleen;

4) gill apparatus;

5) intestinal mucosa;

6) walls of blood vessels;

7) pericardium in teleosts and endocardium in sturgeons.

The head kidney in fish is not separated from the body kidney and consists of lymphoid tissue (erythrocytes and lymphocytes are formed here).

The spleen in fish has a variety of shapes and locations. Lampreys do not have a formed spleen, its tissue is located in the sheath of the intestinal spiral valve. In most fish, the spleen is a separate organ where red blood cells, white blood cells, and platelets are formed, and dead red blood cells are destroyed. In addition, the spleen performs a protective function (phagocytosis of leukocytes) and is a blood depot.

The thymus (goiter or thymus gland) is located in the gill cavity. It distinguishes the superficial, cortical and medulla layers. Lymphocytes are formed in the thymus, it also stimulates their formation in other organs. Thymus lymphocytes are capable of producing antibodies involved in the development of immunity.

The circulatory system includes the heart and the circulatory system. The heart in fish is located near the gills in a small pericardial cavity, in lampreys - in a cartilaginous capsule. The fish heart is two-chambered (one atrium and one ventricle) and includes four sections:

1) atrium (atrium);

2) ventricle (ventriculus cordis);

3) venous sinus, or venous sinus (sinus venosus);

4) arterial cone (conus arteriosus).

The venous sinus is a small thin-walled sac in which venous blood accumulates. From the venous sinus, it enters the atrium, and then into the ventricle. All openings between the sections of the heart are equipped with valves, which prevents the backflow of blood.

In cartilaginous fish, the arterial cone adjoins the ventricle, the wall of the arterial cone is formed, like the ventricle, by cardiac striated muscles, and there is a system of valves on the inner surface (Fig. 19).

In bony fish and cyclostomes, instead of an arterial cone, there is an aortic bulb (bulbus aortae), which is an expanded part of the abdominal aorta. Unlike the arterial cone, the aortic bulb consists of smooth muscles and has no valves.

Lung-breathing fish have a more complex structure of the heart due to the development of pulmonary respiration. The atrium is almost completely divided into two parts by a septum hanging from above, which continues in the form of a fold into the ventricle and arterial cone. Arterial blood from the lungs enters the left side, venous blood from the venous sinus enters the right side, so more arterial blood flows in the left side of the heart, and more venous blood flows in the right side.

The heart of cyclostomes and fish (with the exception of lungfish) contains only venous blood.

The heart rate is specific for each species and depends on the age, physiological state of the fish, and water temperature. In adults, the heart contracts rather slowly - 20-35 times per minute, and in juveniles much more often (for example, in sturgeon fry - up to 142 times per minute). When the temperature rises, the heart rate increases, and when it decreases, it decreases. In many species, during the wintering period, the heart contracts 1-2 times per minute (bream, carp). Blood pressure in the abdominal aorta in cartilaginous fish ranges from 7-45 mm Hg, in bony fish 18-120 mm Hg.

The circulatory system of fish is closed and includes:

1) arteries (vessels that carry blood from the heart);

2) veins (vessels that bring blood to the heart).

Arteries and veins disintegrate in the organs and tissues of fish into capillaries. Fish (except lungfish) have only one circle of blood circulation (Fig. 20).

In bony fish, venous blood from the heart through the aortic bulb enters the abdominal aorta (aorta ventralis), and from it, through the four afferent branchial arteries, into the gills. Oxidized in the gills, arterial blood through the four efferent branchial arteries enters the roots of the dorsal aorta, passing along the bottom of the skull and closing in front, forming a head circle, from which vessels depart to different parts of the head. Behind the branchial region, the roots of the dorsal aorta merge and form the dorsal aorta (a. dorsalis), which runs in the trunk region under the spine. Arteries branch off from the dorsal aorta, supplying internal organs, muscles, and skin with arterial blood. Further

the dorsal aorta goes into the hemal canal of the caudal spine and is called the caudal artery (a. caudalis). All arteries break up into a network of capillaries, through the walls of which there is an exchange of substances between blood and tissues. Blood is collected from capillaries into veins.

The main venous vessels are the anterior and posterior cardinal veins.

From the head, venous blood is collected from the top of the head into the anterior cardinal veins (vena cardinalis anterior); from the lower part of the head (mainly from the visceral apparatus) - into the unpaired jugular (jugular) vein (v. jugularis inferior); from the pectoral fins - into the subclavian veins (v. subclavia).

From the caudal region, venous blood is collected into the caudal vein (vena caudalis), which passes in the hemal canal of the spine under the caudal artery. At the level of the posterior edge of the kidneys, the tail vein is divided into two portal veins of the kidneys (v. portae renalis), which, branching into a network of capillaries in the kidneys, form the portal system of the kidneys. The venous vessels leaving the kidneys are called the posterior cardinal veins (v. cardinalis posterior). On the way to the heart, they receive veins from the reproductive organs, the walls of the body. At the level of the posterior end of the heart, the posterior cardinal veins merge with the anterior ones and form the paired Cuvier ducts (ductus cuvieri), which carry blood into the venous sinus.

From the digestive tract, digestive glands, spleen, swim bladder, blood is collected in the portal vein of the liver (v. portae hepatis), which enters the liver and, branching into a network of capillaries, forms the portal system of the liver. From the liver, blood is collected in the hepatic vein (v. hepatica) and flows directly into the venous sinus.

Thus, fish have two portal systems - the kidneys and the liver. In bony fish, the structure of the portal system of the kidneys and the posterior cardinal veins is not the same. So, in some fish in the right kidney, the portal system of the kidneys is underdeveloped, and part of the blood, bypassing the portal system, immediately passes into the posterior cardinal veins (pike, perch, cod).

Fish have significant differences in the circulatory scheme.

Cyclostomes have eight afferent and as many efferent gill arteries. The supragillary vessel is unpaired, there are no aortic roots. They lack the portal system of the kidneys and the Cuvier ducts, and there is no inferior jugular vein.

Cartilaginous fish have five afferent and ten efferent gill arteries. There are subclavian arteries and veins that provide blood supply to the pectoral fins and shoulder girdle, as well as lateral veins starting from the ventral fins. They pass along the side walls of the abdominal cavity and merge with the subclavian veins in the region of the heart. The posterior cardinal veins at the level of the pectoral fins form extensions - the cardinal sinuses.

In lungfish fish, more arterial blood, concentrated in the left half of the heart, through the abdominal artery mainly enters the anterior afferent branchial arteries, from which it is sent to the head and dorsal aorta; more venous blood from the right half of the heart passes mainly to the posterior afferent branchial arteries, and then to the lungs. During air breathing, the blood in the lungs is enriched with oxygen and enters the left side of the heart through the pulmonary veins. In lungfish, in addition to the pulmonary veins, there are abdominal and large cutaneous veins, and instead of the right cardinal, the posterior vena cava is formed.

The lymphatic system of fish is open. Lymph is a tissue fluid similar in composition to blood plasma; of the blood cells, it contains only lymphocytes. The lymphatic system is connected to the circulatory system and plays an important role in metabolism. During blood circulation, part of the plasma, washing the tissue cells, enters the lymphatic capillaries, and then through the lymphatic system back into the blood.

The lymphatic system is made up of lymphatic capillaries that lead to medium and larger lymphatic vessels that carry lymph to the heart. The lymphatic system, supplementing the function of the venous system, carries out the outflow of tissue fluid.

The largest lymphatic vessels in fish are:

1) paired subvertebrals (pass along the sides of the dorsal aorta from tail to head);

2) paired lateral (pass under the skin along the lateral line).

Through these and head vessels, lymph flows into the posterior cardinal veins at the Cuvier ducts.

Fish also have unpaired lymphatic vessels: dorsal, ventral, spinal. Fish do not have lymph nodes; in some species of fish, under the last vertebrae, there are paired lymphatic hearts in the form of oval bodies that push lymph to the heart. The movement of the lymph is also facilitated by the work of the trunk muscles and respiratory movements. Cartilaginous fish lack lymphatic hearts and lateral lymphatic vessels. In cyclostomes, the lymphatic system is separate from the circulatory system.