External and internal structure of the perch. Internal structure of perch
CLASS BONE FISHES (OSTEICHTHYES)
Lesson 6. DIVERSITY OF BONE FISHES IN CONNECTION WITH EXISTENCE CONDITIONS. EXTERNAL AND INTERNAL STRUCTURE OF BONE FISHES BY THE EXAMPLE OF RIVER PERCH
Systematic object position
Phylum Chordata
Subphylum Vertebrata
Group Jaws (Gnathostomata)
Superclass Pisces
Class Bony fishes (Osteichthyes)
Subclass Ray-finned (Actinopterigii)
Superorder Teleostei
Order Perciformes
Family Percidae
Representative - river perch (Perca fluviatilis)
Equipment and materials
1. Fresh fish (one for two students).
2. Ready-made preparations: 1) opened fish; 2) digestive system; 3) injected circulatory system; 4) brain (one for two students).
3. Dissecting tools: scalpel, scissors, tweezers, dissecting needle, stationery pins (one set for two students).
4. Baths (one for two students).
5. Tables: 1) tables on diversity; 2) appearance bony fish; 3) general location internal organs; 4) digestive system; 5) circulatory system; 6) reproductive organs of the male and female; 7) brain.
Introductory Notes
Variety of bony fish
The class of Bony fishes includes more than 20 thousand modern species. They live in a variety of bodies of water: seas, oceans, rivers, lakes, ponds, streams.
Fish are adapted to a variety of aquatic conditions. They live in bodies of water with varying degrees of salinity, only avoiding oversaturation with salt. They inhabit waters with different temperature conditions: cold-blooded fish (icefish, saber) live in waters with a temperature level of about 0°C. Some freshwater species(crucian carp) are able to survive when water bodies freeze in winter. There are fish in hot springs (from the family Cyprinodontiformes). They have different demands on the oxygen content in water. Bony fish have mastered different depths of the World Ocean and water flows from at different speeds moving water.
Representatives of this class are extremely diverse in their appearance and lifestyle (Fig. 25). According to the nature of connections with the environment, fish are divided into various ecological groups ( life forms). First of all, a distinction is made between marine and freshwater fish. In the seas of the World Ocean live most herrings, cod (haddock, pollock, navaga, cod), tuna, mackerel, garfish, flounder, sailfish, pufferfish and many others. Freshwater bodies of temperate climate
Rice. 25. Environmental groups fish:
Fishes that live in the water column (nektonic; pelagic). Sea: 1 - tuna; 2 - sailboat; 3 - body; 4 - moon fish; freshwater: 5 - crucian carp; 6 - carp; 7 - bream. Bottom fish (benthic). Marine: 8 - flounder; 9 - sand goby; 10 - monkfish; eleven - deep sea anglerfish; freshwater: 12 - common catfish; 13 - loach; 14 - pike. Specific adaptations in fish: 15 - flying fish; 16 - mudskipper
inhabited by representatives of cyprinids (rudd, carp, silver carp, gudgeon, crucian carp, catfish, loach, etc.). Perch species (perch, pike perch, ruffe) and stickleback species also live here. IN tropical waters On different continents live multi-feathers, piranhas, shellfish, etc. There are species that occupy an intermediate position - these are migratory fish. They live either in fresh or salty environments, depending on biological needs: for example, sturgeon and salmon fish go from seas to rivers to spawn, making so-called anadromous migrations, and river eels To spawn, they swim from rivers to the ocean; their migrations are called catadromous.
Inside a reservoir, some fish stay in the water column (nektonic, pelagic), others - near the bottom (bottom, benthic). Habitat leaves its mark on appearance fish. In accordance with this, different ecological types of fish are distinguished. Nektonic (pelagic) fish are usually distinguished by their speed and good buoyancy. Their elongated body is torpedo-shaped (sailfish, mackerel, tuna) or strongly flattened laterally (herring). Fish swim quickly thanks to frequent lateral oscillatory movements of the back of the body, tail and well-developed caudal fin. Some salmon fish overcome the rapid oncoming flows of water and successfully move forward. The speed of a hunting sailboat exceeds 100 km/h, and that of a salmon exceeds 20 km/h.
Among pelagic fish there are species that are not capable of developing higher speed on one's own. They “attach” to the body of a fast-swimming fish (pilots) or stick to it (sticking fish).
The rapid movement of some fish is aided by elongated paired fins. They are used by garfish flying fish. Fleeing from predators, they jump out of the water and cover more than 200 m in a gliding flight.
Many nektonic fish lead a schooling lifestyle, have coordinated behavior and maneuver well in the water.
Bottom fish are rather slow and often lead a solitary lifestyle. Their body is either strongly flattened, like those of flounders, or elongated and laterally compressed closer to the tail, like those of catfish, loaches, and moray eels. Their dorsal and anal fins, their wave-like movements are involved in the slow movements of these fish near the bottom. Some bottom fish modified pectoral fins allow them to quickly move (“crawl”) along the bottom (gurnards, scorpionfish, gobies).
Deep-sea (abyssal) fish species also have specific adaptations.
Based on the nature of their diet, they distinguish: 1) active predators (large sturgeon, sailfish, tuna, etc.); 2) planktivores (herring, anchovies, sunfish); 3) bottom benthic eaters (flounder, eels, anglerfish). In fresh water bodies, active predators are pike-perch, pike, and perch; They eat plankton - roach, rudd, and other cyprinids extract food by digging in the bottom soil; among them there are herbivorous species.
General features of the organization
Despite the great external and systematic diversity, all bony fish are characterized by characteristic features that distinguish them from cartilaginous fish. The skeleton of bony fishes is, to one degree or another, bony of integumentary or chondral origin. In the vast majority of species, the interbranch septa are reduced and the gill filaments sit directly on the gill arches. The gill apparatus is covered with an operculum. There is a swim bladder, an important hydrostatic organ. Fertilization in most bony fish is external, the eggs are small and their quantity is large.
Features of the organization of bony fishes will be considered using the example of the superorder of bony fishes from the subclass of ray-finned fishes, which make up more than 90% of living fish species. Compared to cartilaginous fish, bony fish are characterized by a simplified structure of the skeleton of paired fins: the pectoral and ventral fins lack basalia, and the pelvic fins also lack radials. The pectoral fins are located vertically, under the body. The mouth is located at the end of the head, but can have different positions. The caudal fin is homocercal. The colon does not have a spiral valve. In many bony fish, the intestine has blind (pyloric) outgrowths and ends in the anus. There is no cloaca. The body is covered with bone scales consisting of thin plates. Instead of the arterial cone, the aortic bulb appears.
Study the external and internal structure of the perch.
Consider:
External structure
The body is divided into head, torso and tail; fins: paired - pectoral and abdominal, unpaired - dorsal, subcaudal (anal) and caudal; mouth opening; paired nostrils; eyes; gill covers; lateral line; genital, excretory and anal openings; bone scales.
Digestive system: oral cavity; pharynx; esophagus; stomach; small, thick, rectum; pyloric growths; liver; gallbladder; pancreas.
Respiratory system: four pairs of gills.
Circulatory system: two-chambered heart (atrium and ventricle); aortic bulb; abdominal aorta; four pairs of gill arteries. Using the drug, drawing and table, trace the blood circulation pattern.
Excretory organs: trunk buds; ureters; bladder.
Reproductive organs: testes; ovaries; genital ducts.
Central nervous system: brain (forebrain hemispheres with olfactory lobes, diencephalon, midbrain, cerebellum, medulla); eyes; optic chiasm (chiasm); spinal cord.
Sketch:
1) general location of internal organs; 2) brain (top); 3) diagram circulatory system(homework).
External structure
The body of bony fish, like cartilaginous fish, is divided into the head, body and tail. The boundary between the head and the body is the gill slit, and between the body and the tail is the anus (Fig. 26). The mouth of bony fishes is located at the anterior end of the head, which is why such fish are called limb-stomes in contrast to the transverse-mouthed shark fishes. It can be moved slightly up or down. There are large eyes on the sides of the head. They have a flat cornea and a round lens. Eyelids are missing. Paired nostrils are visible in front - the organs of smell. Each nostril is divided by a valve into two openings: when the fish moves, water enters through the front and exits through the back. This is how the epithelium of the olfactory fossa is washed. The right and left nostrils do not communicate with each other or with the oral cavity.
A characteristic formation for bony fish is the bony operculum. In this regard, instead of five gill openings, like in cartilaginous fish, on the surface of the body bone fish one gill slit is visible. Paired fins, compared to those of cartilaginous fish, are simplified and located in a vertical plane. The caudal fin is homocercal type. The spinal column extends into the upper lobe caudal fin, however, both fin blades are the same. Dorsal fins
Rice. 26. Internal structure of perch:
1 - mouth with teeth; 2 - gill cover (part of it has been removed); 3 - bone scales; 4 - homocercal caudal fin; 5 - dorsal fins; 6 - anal fin; 7 - eye; 8 - nostril; 9 - lateral line; 10 - anus; 11 - genital opening; 12 - excretory opening; 13 - opened stomach with longitudinal folds; 14 - intestines; 15 - pyloric outgrowths; 16 - rectum; 17 - liver; 18 - gallbladder; 19 - pancreas; 20 - gill filaments; 21 - spleen; 22 - swim bladder; 23 - kidney; 24 - ureter; 25 - bladder; 26 - ovary; 27 - atrium; 28 - ventricle; 29 - aortic bulb; 30 - abdominal aorta; 31 - gill rakers
equipped with soft branched or hard spiny rays. The rays are interconnected by a thin leathery membrane.
On the lower side of the body, closer to the rear end, there is a subcaudal, or anal, fin. In front of it, in a common recess, there are three openings: anal, genital and excretory (cartilaginous fish have a cloaca). A clearly visible lateral line stretches along the body - an organ that perceives weak movements of water and infrasonic vibrations.
The body of the bony fish is covered with skin. It distinguishes between the epidermis and cutis. At their border is the basement membrane. In the skin are bone scales. Each scale lies with one edge in a skin pocket. The scales overlap each other in a tiled manner. The structure of the scale can be seen by selecting it with tweezers and examining it against the light or under a microscope. The scales can be cycloid, with a smooth inner edge, or ctenoid, with a jagged edge. Light (wide) and dark (narrow) growth rings are visible on the scales. In summer, with intensive growth of fish, a significant increase in scales occurs - a wide,
light layer. In winter, fish growth and scale growth are insignificant - the layer is compacted, narrow, dark. By counting the light and dark rings on a fish's scales under a microscope, you can determine its age.
The skin glands of the epidermis secrete mucus, which abundantly covers the body of the fish. It promotes better movement of fish in dense aquatic environment. The coloring of fish is characterized by the fact that the dorsal side is usually darker than the belly.
Internal structure
Opening
Take a small fish left hand belly up. Insert the sharp end of the scissors into the anus and make an incision along ventral side body to head, all the way to the mouth. In this case, you need to press the scissors from the bottom up, without lowering their ends deep, so as not to damage the internal organs. Cut across the shoulder girdle that is in the path of the cut. After making a longitudinal incision, place the fish on its right side, insert the blunt end of the scissors into the incision made near the anus and cut the body wall upward, towards the lateral line. Make a second transverse incision near the operculum. Next, make a longitudinal cut along the lateral line, connecting both transverse cuts. Unscrew the resulting flap of fabric and remove it.
At the anterior end of the body, expose the gills and heart. To do this, cut off the gill cover and shoulder girdle. The heart lies almost immediately under the gills. To expose the brain, the skull cap must be carefully removed. Take the fish in your left hand with its back up, head away from you. Make a transverse incision with scissors in the back of the brain case at the back of the head. Make the side cuts along the edges of the skull forward. Finish with a cross-cut at the front of the head (in front of the eyes). Grasp the skull roof with tweezers and carefully remove it. View the brain from above.
To view the brain from below, you need to cut the medulla oblongata and tilt the brain forward. To examine the structure of the eye, it should be removed from the eye orbit.
General location of internal organs
Using an opened fish, let's look at the general location of the internal organs (see Fig. 26). The trunk muscles are clearly visible under the skin. It has a metameric structure.
Under the operculum lie four pairs of gill arches, on which there are gills, and behind them, below them, there is a two-chambered heart. In front of the ventricle, there is a noticeable expansion of the abdominal aorta - the aortic bulb, from which the abdominal aorta originates. In the anterior abdominal cavity, a large liver covering the stomach is clearly visible. There is a gallbladder, the duct of which opens into duodenum. The intestinal tube extends from the stomach. Pyloric growths are visible at the border of the stomach and intestines. The pancreas of most fish is located dispersedly between the stomach and the adjacent intestinal loop. In one of the intestinal loops there is a dark burgundy spleen.
In the back of the body cavity lie the genital organs - the testes or ovaries. The degree of their development depends on the season in which the fish was caught and its age. The testes are distinguished by their milky-cream color, which is why they are called milts. The ovaries are represented by elongated bags of yellowish-orange color with a granular structure (caviar).
Above all the abdominal organs, under the spinal column, lies the swim bladder. It is known that it is absent in cartilaginous fish. The swim bladder is embryonically formed from the dorsal wall of the intestine. This is an important hydrostatic organ that allows fish in the water column to maintain the density of their body in balance with the buoyant force and gravity, maintaining neutral buoyancy at each depth. With the help of the swim bladder, the fish can perceive external pressure and transmit its changes to the balance organs. In some fish, the swim bladder can serve as a respiratory organ and contribute to the perception and production of sounds. Under the spine, dark red buds stretch along the upper side of the body cavity. Bony fish have a bladder.
Organ systems
Digestive system
The digestive system of bony fish in comparison with that of cartilaginous fish is elongated, but less differentiated. The intestine is represented by a homogeneous tube, and the boundaries between the foregut, middle and hindgut are difficult to notice.
The mouth is equipped with jaws that bear teeth. Often the teeth sit on the vomer and gill bones. The oral cavity passes into the wide pharynx, which, in turn, into the short esophagus and stomach. The size and shape of the stomach depends on the nature of the diet. In carnivores
In fish (for example, perch), the stomach is voluminous, capable of stretching, and differs sharply from subsequent sections of the intestine. If swallowed large production stomach predatory fish expands due to stretching of the longitudinal folds of its walls. In herbivorous fish (for example, cyprinids), the boundaries between the stomach and intestines are little noticeable. The intestines extend from the stomach. In bony fish, unlike elasmobranchs, it is longer and forms loops. In many fish, the increase in the absorptive surface of the intestine is carried out due to the caeca, pyloric processes extending from the anterior part of the small intestine. U river perch There are three pyloric outgrowths; in some salmon fish their number reaches four hundred. Carp, pike, and catfish do not have them.
The ducts of the liver, gallbladder and pancreas flow into the anterior section of the small intestine - the duodenum. Under the influence of enzymes in the alkaline environment of the intestine, the main components of food are broken down.
The small intestine smoothly passes into the large intestine, then comes the rectum, which ends at the anus (anus).
All fish have a developed liver - an important digestive gland. Its secret: bile accumulates in the gallbladder, and then bile ducts enters the anterior intestine. Bile emulsifies fats and activates the enzyme that breaks down fat (lipase). In addition to participating in digestion, the liver plays an important role in detoxifying toxic substances And harmful products metabolism. Therefore, it is called a barrier organ. Glycogen accumulates in the liver and urea is formed.
The second digestive gland - the pancreas - is usually located diffusely or in the form of lobules on the mesentery at the beginning of the small intestine. In some fish (for example, pike) it is a compact formation, in others (cyprinids) it is scattered in the form of small fat-like inclusions between the bends of the intestinal tube. The pancreas secretes a complex of digestive enzymes that break down proteins, fats and carbohydrates. At the same time, it is an endocrine gland that ensures the balance of carbohydrate metabolism.
Respiratory system
The gill apparatus of bony fish, in contrast to that of cartilaginous fish, is characterized by the absence of interbranchial septa. The gill filaments sit directly on the gill arches (Fig. 27). There is an operculum - a hard bony plate,
Rice. 27. Gills of a shark (A, C) and bony fish (B, D):
A - frontal section through the oropharyngeal cavity of the shark; B - the same as bony fish; B - cross section through the gill of a shark; G - the same for bony fish: 1 - oropharyngeal cavity; 2 - esophagus; 3 - jaw arch; 4 - hyoid arch; 5 - spray bottle; 6 - internal gill slits; 7 - external gill slits; 8 - gill cover; 9 - gill arches; 10 - gill filaments; 11 - interbranchial septa
covering the gills, as a result of which only one gill opening is preserved.
Each gill of bony fishes is composed of two semi-gills attached to a bony gill arch, to which gill filaments are attached. They are pierced by the capillaries of the afferent branchial artery. Like cartilaginous fish, the gill filaments are of ectodermal origin. On inside Gill rakers are located on the gill arches, forming a kind of filtering apparatus - a sieve that prevents food from penetrating to the gills, but allows water to enter the peribranchial cavity. In bony fishes, four pairs of gill arches are well developed, the arch of the fifth pair is greatly shortened.
On the inner side of the operculum, one can note the remains of an additional semi-branch - a pseudobranch. She most likely does not take an active part in the exchange of gases.
The act of respiration of bony fish is carried out thanks to the sucking mechanism due to the movement of the gill cover. When the operculum is raised, the thin, leathery gill membrane located along the edge of the operculum is pressed against the gill slit under the influence of external water pressure. As a result, a space with
low blood pressure. This causes the flow of water entering through the mouth to rush through the pharynx into the peribranchial cavity. When the lid is lowered, excess pressure is created in the peribranch cavity and water, pushing each gill cover aside, is pushed out through the external gill openings. When the fish moves rapidly, the current of water passes through the gill apparatus without the participation of the gill covers (ram type of breathing).
Circulatory system
The circulatory system of bony fish, when compared with the circulatory system of cartilaginous fish, differs in some features. Thus, in bony fish (Fig. 28), in the initial part of the abdominal aorta, instead of the arterial cone, an aortic bulb develops. It is a thickening of the aorta and has, like everyone else, blood vessels, smooth muscles. There are only four pairs of afferent and efferent gill arteries (cartilaginous fish have five pairs). The lateral veins disappear. The heart is located on the ventral side of the body near the head. It is enclosed in the pericardial sac. The dark burgundy atrium is clearly visible. Above the atrium is the venous sinus (sinus), which looks like a funnel and collects venous blood from the entire body. Bottom to
Rice. 28. Diagram of the circulatory system of a bony fish:
1 - atrium; 2 - ventricle; 3 - aortic bulb; 4 - abdominal aorta; 5 - afferent gill arteries; 6 - efferent branchial arteries; 7 - aortic roots; 8 - dorsal aorta; 9 - carotid arteries; 10 - subclavian arteries; 11 - tail vein; 12 - right posterior cardinal vein; 13 - left posterior cardinal vein; 14 - renal portal system; 15 - subintestinal vein; 16 - portal system of the liver; 17 - duct of Cuvier; 18 - hepatic vein; 19 - anterior cardinal or jugular veins; 20 - left portal vein of the kidney. Vessels containing venous blood are painted black.
The atrium is adjacent to a bright red muscular ventricle. The difference in color of the atrium and ventricle is due to the thickness of their walls. In the thin-walled atrium, venous blood shines through and creates a darker color tone of its wall. Thick muscular walls are clearly visible in the ventricle.
The abdominal aorta extends forward from the ventricle, which at its base expands into the aortic bulb. (Remember that in elasmobranch fishes the arterial cone lies in this place.) From the abdominal aorta, blood is directed through the afferent gill arteries to the gills, in the capillaries of which it gives off carbon dioxide, then flows through the efferent branchial arteries into the paired roots of the aorta and then goes to the dorsal aorta. The vessels that carry arterial blood to the head are called carotid arteries.
The dorsal aorta, which lies under the spine, carries blood to the tail. This aorta gives branches to all organs: the stomach, intestines, genitals, kidneys, fore and hind limbs. On the body of an opened fish, the dorsal aorta is clearly visible between the kidneys.
Venous blood, as in cartilaginous fish, returns to the heart through the azygos caudal vein and through the paired posterior and anterior cardinal (jugular) veins. The posterior cardinal veins, passing through the kidneys, break up into a network of capillaries, forming the renal portal system.
The posterior cardinal veins on each side of the body merge with the anterior cardinal veins to form the ducts of Cuvier. The intestinal vein passes through the liver, breaking up there into capillaries and forming the portal system of the liver. A short hepatic vein emerges from the liver and flows into the sinus venosus.
Excretory organs
The excretory organs of bony fish are similar to those of cartilaginous fish. The difference is that the excretory system in bony fish is not connected to the reproductive organs.
Long dark red trunk kidneys (mesonephric) lie on the sides of the spine above swim bladder. The ureters are the Wolffian canals, which run along the inner edge of the kidneys. Bony fish have a developed bladder.
Reproductive organs
Unlike cartilaginous fish, female bony fish lack Müllerian canals. The thin membrane of the sac-shaped ovary continues into a narrow duct. A mature egg is thrown over it
out. In males, reproductive products are ejected through the vas deferens and their gonads are not connected to the Wolffian canals. Thus, the Wolffian channel performs only one function - the removal of metabolic products, i.e. ureter.
The separation of the reproductive and excretory systems of bony fishes is apparently due to the abundance of reproductive products.
Depending on the season and age of the fish, the degree of development of the reproductive organs may vary. In young specimens or in individuals caught outside the breeding season, the genitals are poorly developed. During the breeding season, the size of the gonads increases greatly.
central nervous system
Relative sizes brain in general, they increase in bony fish compared to cartilaginous fish (Fig. 29). However, the forebrain is relatively small. It is divided into two hemispheres by a longitudinal groove. The roof of the hemispheres does not contain nerve cells, it is epithelial. The main mass of the forebrain consists of the striatal bodies lying in its thickness. In front, the olfactory bulbs with olfactory nerves leading to the nasal capsules are visible. The cavities inside the hemispheres form two cerebral ventricles.
Diencephalon covered from above by the cerebral hemispheres and midbrain. The epiphysis (endocrine gland) is located on top of it, and the pituitary gland (endocrine gland) is adjacent to the bottom. Inside is the cavity of the third ventricle.
Midbrain in bony fishes it is noticeably larger than other sections. Two large optic lobes are visible from above. The cerebellum is also quite large, especially in active fish species. It significantly covers the medulla oblongata.
Medulla elongated and gradually passes into the spinal cord. A diamond-shaped pattern is visible from above
Rice. 29. Perch brain from above:
1 - nasal capsule; 2 - olfactory lobes of the forebrain; 3 - forebrain; 4 - midbrain; 5 - cerebellum; 6 - medulla oblongata; 7 - spinal cord; 8 - diamond-shaped fossa; 9 - olfactory nerves
the fossa is the fourth ventricle of the brain. When examining the brain from below, the forebrain with the olfactory lobes, a rounded outgrowth on diencephalon- the pituitary gland and in front of it - the optic chiasm (chiasm). From the brain of bony fish, like cartilaginous fish, 10 pairs of cranial nerves depart.
Spinal cord lies in the canal formed by the upper vertebral arches.
Perch is one of the most common fish in our freshwater bodies of water and one of the most favorite objects of “hunting” for amateur fishermen, both in summer and winter.
There is already an article about that on the site. There we're talking about about why this striped predator so loved by fans of winter fishing. And here I would like to introduce readers in more detail to this wonderful fish.
During zoology classes in high school, we all studied the “Fish” section using perch as an example. I remember well how, at the request of the teacher, I myself brought laboratory lesson in 7th grade there were several perches, which we dissected ourselves, studying the internal structure of the fish. It was a long time ago, more than 40 years ago.
Nowadays they hardly do this anywhere in school lessons. Yes, and there is no need for this. After all, there are not only colorful textbooks with all the diagrams and drawings, but various, as they say now, interactive materials with which you can “dissect” a perch on a computer screen. So students have the opportunity to study the structure of a perch, even if they have never caught one in their lives, but have never even seen one.
I accidentally looked into an old zoology textbook (1977) for grades 6-7 high school. I looked at how, using the example of perch, children were taught (and are now taught) the zoology of fish in our schools, although this fish has many features that distinguish it from others.
It’s no coincidence that L.P. Sabaneev gave this description of the appearance of the perch: "In its appearance and body color, perch is easily distinguished from all our other fish. Its body is quite wide, especially in large perches, and somewhat humpbacked; the back is dark green, the sides are greenish-yellow, the belly is yellowish; 5-9 transverse dark stripes stretch across the entire body, which make it very motley; in some cases, these stripes are replaced by dark, irregular spots. In addition, the caudal fin, especially in its lower part, the anus and ventral fins are bright red; The pectoral fins are yellow, the first dorsal fin is gray, with a large black spot at the end, the second is greenish-yellow. The eyes are orange. However, the color of the perch depends, like most fish, on the quality of the water, and even more on the color of the soil. So dip in clear water with a light sandy or clayey bottom, they are very light, sometimes even without a black eye on the dorsal feather and with inconspicuous transverse stripes. On the contrary, in forest lakes with a black muddy bottom they have darker stripes, a darker back and a bright yellow belly. In some areas (as, for example, in Lake Senezhskoe, Moscow province) perches even have golden gill covers. In addition, it should be noted that young perches up to the age of two are of the same color, having reached sexual maturity, and that the largest ones are comparatively darker. On the gill covers there is one sharp spine, which pricks very painfully and can even cause swelling and mild inflammation. The mouth is very large, armed with numerous but very small teeth.
I photographed the drawings from this old textbook to clearly demonstrate the structure of the perch.
The external structure of the perch is shown in the first picture. Perch, like most fish, has a streamlined body shape that allows it to move quickly in the water.
The perch's head smoothly transitions into the body, and the body into the tail. At the pointed front end of the head there is a mouth with lips that can open wide. On the top of the head two pairs of small holes are visible - nostrils leading to the olfactory organ. On its sides there are two large eyes.
But what description of perch is given in more scientific work- Key to freshwater fish of the USSR fauna. (author Veselov E.A., M. Prosveshchenie, 1977, p. 178): " The body is laterally compressed, oval, covered with small scales. The cheeks are completely covered with scales. There are no fangs. The gill membranes are not fused to each other. Gill rays 7. Two dorsal fins, not fused together; in the first fin there are from 13 to 16 spiny rays, in the second - from 1 to 3 unbranched rays and from 13 to 15 branched rays. The anal fin has 2 unbranched and 8-9 branched rays. There are 57-77 scales in the lateral line. There are 14-20 gill rakers. The pelvic fins are slightly longer than the pectoral fins. Body greenish-yellow. There are 5-9 transverse black stripes on the sides. Fins: dorsal - gray (with a black spot), second dorsal - greenish-yellow. Breasts are yellow, the rest are red."
The Latin name for perch is also given - Perca fluviatilis Linne.
In a school textbook about fins it is written in simpler language: “Bending the body and tail now to the right, now to the left, the perch moves forward. The fins help this. Each of them is a double layer of skin supported by hard bony fin rays. Many of them are transformed in the perch into sharp spines. When perch is attacked by enemies (enemies of perch - catfish, pike, burbot, aquatic birds), the splayed spines of the fins provide protection. There are unpaired fins - dorsal (perch has two), caudal and subcaudal (anus) and paired - pectoral. and abdominal. Main role When moving forward, the caudal fin plays. Paired fins serve as rudders of depth, and are also important when turning, stopping, moving slowly forward and maintaining body balance." I would like to add that these fins allow the perch to move not only forward, but also slowly “back away.” I have seen this more than once into the hole, as the perch slightly moves its fins and moves back from the bait, which it did not like.
Perch is not the fastest swimmer among fish. A pike, for example, can reach a much higher speed when throwing itself at a prey, but a perch can swim at speeds of up to 20-22 km/h while chasing a fry.
Cover and color of perch.
The body of the perch is covered with bony scales, each of which with its rear edge overlaps the scales of the next row, forming a protective layer - scales that do not interfere with body movements. Perch scales are so strong that it is difficult to tear them off even when cleaning with a knife. The scales are covered on top with thin skin, the glands of which secrete mucus, which reduces friction with water during movement and serves as protection against bacteria and mold.
The belly of the perch is lighter than the back, which serves as a good camouflage. From above, the dark back is less noticeable against the background of the dark bottom, and the light belly is less noticeable from below against the light background of the water surface. Dark stripes on the greenish sides help the perch to camouflage perfectly in thickets of river grass. The color of perches varies greatly depending on the bodies of water in which they live. In muddy, peaty lakes, perches have a very dark, almost black color, and in reservoirs with a sandy bottom there are perches with a very light, bright color. The protective coloration helps the perch hide from enemies and lie in wait for its prey in ambush.
Fish - aquatic animals, adapted to life in fresh water bodies and sea water. They have a hard skeleton (bone, cartilaginous or partially ossified).
Let us consider the structural features and vital functions of fish using the example of river perch.
Habitat and external structure fish using the example of river perch
River perch lives in freshwater bodies (slowly flowing rivers and lakes) in Europe, Siberia and Central Asia. Water exhibits noticeable resistance to bodies moving in it. Perch, like many other fish, has streamlined shape- this helps him move quickly in the water. The perch's head smoothly transitions into the body, and the body into the tail. At the pointed front end of the head there is a mouth with lips that can open wide.
Figure: external structure of river perch
On the top of the head two pairs of small holes are visible - nostrils leading to the olfactory organ. On its sides there are two large eyes.
Perch fins
Bending the laterally flattened body and tail first to the right and then to the left, the perch moves forward. When swimming big role fins play. Each fin consists of a thin membrane of skin, which is supported by bony fin rays. When the rays spread out, the skin between them tightens and the surface of the fin increases. On the back of the perch there are two fin pins: front big And the rear one is smaller. Number dorsal fins May be different for different fish species. At the end of the tail there is a large two-lobed caudal fin, on the underside of the tail - anal. All these fins are unpaired. Fish also have paired fins - there are always two pairs of them. Pectoral fins(front pair of limbs) are placed on the sides of the perch’s body behind the head, paired pelvic fins (back pair of limbs) are on the underside of the body. The main role in moving forward is played by caudal fin. The paired fins are important for turning, stopping, moving forward slowly, and maintaining balance.
The dorsal and anal fins give the fish body stability when moving forward and making sharp turns.
Cover and color of perch
The body of the perch is covered bone scales. Each scale with its front edge is immersed in the skin, and with its rear edge it overlaps the scales of the next row. Together they form a protective cover - scales that does not interfere with body movements. As the fish grows, the scales also increase in size and can be used to determine the age of the fish.
The outside of the scales is covered with a layer of mucus, which is secreted by the skin glands. Mucus reduces friction between the fish's body and water and serves as protection against bacteria and mold.
Like most fish, the belly of the perch is lighter than the back. Top back to to a certain extent merges with dark background bottom. From below, the light belly is less noticeable against the light background of the water surface.
The body color of a perch depends on environment. In forest lakes with a dark bottom it has dark color, sometimes even completely black perches are found there. Perches with light and bright colors live in reservoirs with a light sandy bottom. Perch often hides in thickets. Here the greenish color of its sides with vertical dark stripes makes the perch invisible. This protective coloring helps him hide from enemies and better watch over his prey.
Along the sides of the perch's body from head to tail runs a narrow dark lateral line. This is a kind of sensory organ.
Skeleton of a river perch
The skeleton of a perch consists of large number bones. Its basis is the spine, which stretches along the entire body of the fish from the head to the caudal fin. The spine is formed a large number vertebrae (perch has 39-42).
Figure: Skeleton of a river perch
When a perch develops in the egg, a notochord appears in the place of its future spine. Later, vertebrae appear around the notochord. In adult perch, only small cartilaginous remains between the vertebrae are preserved from the notochord.
Each vertebra consists of body And upper arch, ending in a long upper process. Taken together, the upper arches together with the vertebral bodies form the spinal canal, which contains spinal cord.
IN trunk region the bodies are attached to the vertebrae laterally ribs. There are no ribs in the caudal region; each vertebra located in it is equipped with a lower arch ending in a long lower process.
In front, the skeleton of the head is firmly articulated with the spine - scull. There is also a skeleton in the fins.
In paired pectoral fins, the skeleton of the fins is connected to the spine by bones shoulder girdle. The bones connecting the skeleton of the paired pelvic fins to the spine are not developed in the perch.
The skeleton has great importance: It serves as a support for muscles and protection for internal organs.
River perch muscles
Under the skin there are muscles attached to the bones that form muscles. The strongest of them are located on dorsal side body and caudal region.
The contraction and relaxation of muscles causes the fish's body to bend, allowing it to move in the water. The head and fins contain muscles that move the jaws, gill covers and fins.
Swim bladder of river perch
River perch, like any fish, is heavier than water. Its buoyancy ensures swim bladder. It is located in the abdominal cavity above the intestines and has the shape of a translucent sac filled with gas.
Figure: Internal structure of river perch. Digestive and excretory systems
The swim bladder is formed in the perch embryo as an outgrowth of the intestine on the dorsal side. It loses connection with the gut during the larval stage. The larva should float to the surface of the water 2-3 days after hatching and swallow a little atmospheric air to fill the swim bladder. If this does not happen, the larva cannot swim and dies.
By regulating the volume of the swim bladder, the perch stays at a certain depth, floats up or sinks. When the bladder contracts, excess gas is absorbed by the blood in the capillaries inner surface bubble If the bubble expands, gas enters it from the blood. When the perch sinks into the depths, the bubble decreases in volume - and the density of the fish increases. This promotes rapid immersion. When floating, the volume of the bubble increases and the fish becomes relatively lighter. At the same depth, the volume of the fish's bladder does not change. This allows the fish to remain motionless, as if hanging in the water column.
Unlike river perch, in other fish, such as carp, bream, roach, herring, the swim bladder remains connected to the intestine using an air duct - a thin tube throughout life. Excess gas exits through this duct into the intestines, and from there through the mouth and gill slits into the water.
The main function of the swim bladder is to provide buoyancy for fish. In addition, it helps fish hear better, since, being a good resonator, it amplifies sounds.
Fish - aquatic animals, adapted to life in fresh water and sea water. They have a hard skeleton (bone, cartilaginous or partially ossified).
Let us consider the structural features and vital functions of fish using the example of river perch.
Habitat and external structure of fish using the example of river perch
River perch lives in freshwater bodies of water (slow-flowing rivers and lakes) in Europe, Siberia and Central Asia. Water exhibits noticeable resistance to bodies moving in it. Perch, like many other fish, has a streamlined shape - this helps it move quickly in the water. The perch's head smoothly transitions into the body, and the body into the tail. At the pointed front end of the head there is a mouth with lips that can open wide.
Figure: external structure of river perch
On the top of the head two pairs of small holes are visible - nostrils leading to the olfactory organ. On its sides there are two large eyes.
Perch fins
Bending the laterally flattened body and tail first to the right and then to the left, the perch moves forward. When swimming, fins play an important role. Each fin consists of a thin membrane of skin, which is supported by bony fin rays. When the rays spread out, the skin between them tightens and the surface of the fin increases. On the back of the perch there are two fin pins: front big And the rear one is smaller. The number of dorsal fins may vary between different fish species. At the end of the tail there is a large two-lobed caudal fin, on the underside of the tail - anal. All these fins are unpaired. Fish also have paired fins - there are always two pairs of them. Pectoral fins(front pair of limbs) are placed on the sides of the perch’s body behind the head, paired pelvic fins (back pair of limbs) are on the underside of the body. The main role in moving forward is played by caudal fin. The paired fins are important for turning, stopping, moving forward slowly, and maintaining balance.
The dorsal and anal fins give the fish body stability when moving forward and making sharp turns.
Cover and color of perch
The body of the perch is covered bone scales. Each scale with its front edge is immersed in the skin, and with its rear edge it overlaps the scales of the next row. Together they form a protective cover - scales that does not interfere with body movements. As the fish grows, the scales also increase in size and can be used to determine the age of the fish.
The outside of the scales is covered with a layer of mucus, which is secreted by the skin glands. Mucus reduces friction between the fish's body and water and serves as protection against bacteria and mold.
Like most fish, the belly of the perch is lighter than the back. From above, the back to a certain extent merges with the dark background of the bottom. From below, the light belly is less noticeable against the light background of the water surface.
The body color of a perch depends on the environment. In forest lakes with a dark bottom it has a dark color, sometimes even completely black perches are found there. Perches with light and bright colors live in reservoirs with a light sandy bottom. Perch often hides in thickets. Here the greenish color of its sides with vertical dark stripes makes the perch invisible. This protective coloring helps him hide from enemies and better watch over his prey.
Along the sides of the perch's body from head to tail runs a narrow dark lateral line. This is a kind of sensory organ.
The skeleton of a perch consists of a large number of bones. Its basis is the spine, which stretches along the entire body of the fish from the head to the caudal fin. The spine is formed by a large number of vertebrae (perch has 39-42).
Figure: Skeleton of a river perch
When a perch develops in the egg, a notochord appears in the place of its future spine. Later, vertebrae appear around the notochord. In adult perch, only small cartilaginous remains between the vertebrae are preserved from the notochord.
Each vertebra consists of body And upper arch, ending in a long upper process. Taken together, the upper arches together with the vertebral bodies form the spinal canal, which contains spinal cord.
In the trunk section of the body, they are attached to the vertebrae at the sides ribs. There are no ribs in the caudal region; each vertebra located in it is equipped with a lower arch ending in a long lower process.
In front, the skeleton of the head is firmly articulated with the spine - scull. There is also a skeleton in the fins.
In paired pectoral fins, the skeleton of the fins is connected to the spine by bones shoulder girdle. The bones connecting the skeleton of the paired pelvic fins to the spine are not developed in the perch.
The skeleton is of great importance: it serves as a support for muscles and protection for internal organs.
River perch muscles
Under the skin there are muscles attached to the bones that form muscles. The strongest of them are located on the dorsal side of the body and in the tail.
The contraction and relaxation of muscles causes the fish's body to bend, allowing it to move in the water. The head and fins contain muscles that move the jaws, gill covers and fins.
Swim bladder of river perch
River perch, like any fish, is heavier than water. Its buoyancy ensures swim bladder. It is located in the abdominal cavity above the intestines and has the shape of a translucent sac filled with gas.
Figure: Internal structure of river perch. Digestive and excretory systems
The swim bladder is formed in the perch embryo as an outgrowth of the intestine on the dorsal side. It loses connection with the gut during the larval stage. On the 2-3rd day after hatching, the larva should float to the surface of the water and swallow some atmospheric air to fill the swim bladder. If this does not happen, the larva cannot swim and dies.
By regulating the volume of the swim bladder, the perch stays at a certain depth, floats up or sinks. When the bladder contracts, excess gas is absorbed by the blood in the capillaries of the inner surface of the bladder. If the bubble expands, gas enters it from the blood. When the perch sinks into the depths, the bubble decreases in volume - and the density of the fish increases. This promotes rapid immersion. When floating, the volume of the bubble increases and the fish becomes relatively lighter. At the same depth, the volume of the fish's bladder does not change. This allows the fish to remain motionless, as if hanging in the water column.
Unlike river perch, in other fish, such as carp, bream, roach, herring, the swim bladder remains connected to the intestine using an air duct - a thin tube throughout life. Excess gas exits through this duct into the intestines, and from there through the mouth and gill slits into the water.
The main function of the swim bladder is to provide buoyancy for fish. In addition, it helps fish hear better, since, being a good resonator, it amplifies sounds.
We recommend starting to become familiar with the internal structure of bony fish by studying the features of the location of systems and organs using the materials presented in the lesson manuals, look at the pictures and diagrams. After theoretical preparation, proceed to the task on fish dissection .
Digestive system bony fish, compared to cartilaginous fish, has a number of differences. Overall, she less differentiated than in cartilaginous fish, especially in the intestinal area, where practically there are no clear boundaries between its departments.
The digestive tract begins oral cavity , in which they are located language (as in cartilaginous fish, does not have its own muscles) and bone teeth. The shape and number of teeth vary considerably among different species. Predatory fish have numerous sharp teeth, directed with their ends somewhat back, towards the pharynx, which helps to hold slippery prey. Some fish have teeth small needle-shaped(herring, carp species).
Some bottom fish (pufferfish, flounder, wrasse, etc.) have teeth in in the form of large plates, with the help of which dense plant tissues are crushed, shells and shells of benthic species (crustaceans, echinoderms) are crushed. This is also facilitated by powerful pharyngeal teeth, sitting on the last pair of gill arches.
Throughout life there is change of teeth, but it is irregular. In this case, new teeth grow in the spaces between existing teeth. Planktivorous fish(herring, carp) are deprived dental apparatus and have a peculiar filter device in the form of gill rakers that help filter plankton.
The oral cavity is followed wide throat , short esophagus , passing Vstomach . The size and shape of the stomach are determined by the type of food. U predatory fish (perch, pike) the stomach is more voluminous, with easily extensible walls and sharply demarcated from the intestine. Against , boundaries between the stomach and intestines herbivores fish (species of carp fish - silver carp, grass carp, etc.) little noticeable.
departs from the stomach intestines in the form of a long round tube forming a loop, but without external divisions into departments. In front small intestine there are special formations - pyloric growths, which delay the passage of food and increase the absorption surface of the intestine. In fact, they perform the same function as the spiral valve of cartilaginous fish. River perch has only three pyloric outgrowths, but in some fish (salmonids) their number reaches two hundred.
Anterior section the small intestine is duodenum, where do they flow liver ducts andpancreas. The liver is well developed in all fish. Entering small intestine bile with the enzymes it contains, it promotes active digestion of food. In addition, the liver produces urea, accumulates glycogen. It also plays an important role in neutralizing toxic substances ( barrier organ).
Pancreas in many fish it is represented in in the form of small fat-like formations, lying on the mesentery in the bends of the intestinal tube. In some fish (pike) it is more compact.
Small intestine imperceptibly turns into thick, next comes rectum which ends anus.
Respiratory system bony fish gill type, presented four pairs gills; fifth – unpaired and greatly reduced. In the gill apparatus, unlike cartilaginous fish, no partitions separating the gills. The basis of each gill is arc(Fig. 26), on internal the side on which the short bones are located stamens, representing a filtering apparatus. It prevents food from coming back out.
WITH external the sides of the arc are soft gill filaments where capillaries branch and gas exchange occurs. Attached to the inner side of the gill cover is a rudimentary falsebranch, has lost its gas exchange function. Gill cover, covering the opening leading to the gills, is a hard plate consisting from several bones elements.
Breathing mechanism bony fishes are carried out mainly due to the movements of the gill cover, which ensures a constant flow of water through the mouth and gill apparatus. When inhaling, the gill covers move to the sides, and their thin leathery membranes are pressed against the gill openings. Due to this, a space with reduced pressure is formed in the peribranchial cavity; water enters the oropharyngeal cavity through the mouth opening and washes the gills. When the lids move back, excess pressure is created and water, bending their leathery edges, comes out through the holes.
With this method of breathing, fish are able to absorb up to 46–82% oxygen, dissolved in water. Some fish living in oxygen-deficient waters develop and other devices: cutaneous respiration can account for up to 20–30% or more of the total gas exchange; there are fish that additionally use atmospheric oxygen, capturing air with your mouth from the surface of the water.
Circulatory system bony fish (Fig. 27), compared to cartilaginous fish, is different a number of signs. Instead of an arterial cone, it departs from the ventricle aortic bulb, which has smooth muscles and is the beginning of the abdominal aorta. In the area of the gill apparatus only four pairs of bringing and carrying out arteries.
The venous system has also undergone changes: no side veins; occurs in many species asymmetry of the renal portal system- only left cardinal vein forms a capillary network in the kidney tissue, the right cardinal vein passes through the kidney without interruption.
On the ventral side of the front part of the body is located heart , which is contained in pericardial sac. TO atrium , having smooth muscles and a dark burgundy color, adjacent venous sinus where venous blood collects. Departs from the atrium ventricle , characterized by a bright red color and thick muscular walls. The difference in coloring of the atrium and ventricle is due to the thickness of the walls - venous blood is visible in the thin-walled atrium.
Departs from the ventricle abdominal aorta, the beginning of which is aortic bulb. Blood from the abdominal aorta gill bearers arteries is sent to the gills, where it is enriched with oxygen, then along enduringgill arteries flow into steam rooms aortic roots. From the roots of the aorta are formed carotid arteries and dorsal aorta, breaking up into smaller arteries that carry blood to organs and tissues (in an opened fish, the dorsal aorta is clearly visible between the kidneys).
From the back of the body, venous blood collects through unpaired caudal vein, which splits into paired rear cardinal. Moving away from the head anterior cardinal(jugular), which at the level of the heart merge with the posterior cardinal veins to form Cuvier's ducts. The portal system is present only in the left kidney (see above). The portal system of the liver is formed by unpairedsubintestinalvein. From the liver, venous blood enters the hepatic veins into the venous sinus.
Excretory system. Excretory organs of bony fish similar to those of cartilaginous fish, however not related to the reproductive system. Trunk buds (mesonephros) long, dark red in color and located on the sides of the spine above the swim bladder. The ureters serve willfov channels, which stretch along the inner edge of the kidneys. Bony fish have bladder .
Reproduction system. Bony fish are dioecious; As a rare case, there is a manifestation of hermaphroditism (sea bass). The reproductive system is represented in males testes , in females - ovaries . The gonads of both males and females have independent ducts. In males wolf channel performs only the function of urination. Elongated structures extend from the ovaries, ending in a genital opening through which eggs are laid out ( Müllerian canals are absent).
Central nervous system and sensory organs.
Like other vertebrates, central nervous system comprises head And spinal sections.
Brain in bony fishes, in general, relatively larger in size, but of a more primitive structure than that of cartilaginous fish: forebrain relatively small, in his roof absent nervous substance, cavities cerebral hemispheres (lateral ventricles) not separated partition . The most pronounced development midbrain and cerebellum.
Forebrain looks like small hemispheres in which there is no brain matter (their epithelial roof). The main part of the hemispheres consists of the so-called striatum, lying on the bottom. In the front are olfactory lobes, the sizes of which are inferior to those of cartilaginous fish.
Diencephalon covered by the anterior and middle parts of the brain. In its back part there is a small endocrine gland - pineal gland and on the lower side there is a rounded outgrowth - pituitary.
Midbrain It has large optic lobes , where incoming processing takes place visual information, and the abdominal part contains communication centers with the cerebellum, medulla oblongata and spinal cord.
Cerebellum overlaps the midbrain and significantly covers the beginning medulla oblongata, which has rhomboid fossa(fourth ventricle). The cerebellum determines the activity of somatic muscles, the activity of movement and the maintenance of balance.
Like cartilaginous fish, from the brain ten pairs of nerves arise , coordinating the work of systems and organs.
The spinal cord does not have any special differences in comparison with cartilaginous fish, but the autonomy of its functions is less pronounced.
Sense organs bony fish are diverse, but the most important in their life are smell and taste.
Despite the weak development of the olfactory lobes of the forebrain, compared with cartilaginous fish, the resolution in capturing smells in most bony fishes it is quite high, especially in schooling and migratory fishes. This is due to the special structure olfactory bags which have well-developed folds olfactory epithelium And flickering eyelashes, increasing the flow of water through the nasal openings.
Taste buds, defining the function taste , located in the oral mucosa, on the antennae, body surface and fins. They allow you to clearly recognize all taste sensations - bitter, sweet, sour and salty.
Lateral line organs well developed and represent channels passing through the thickness of the skin. With the help of small holes in the scaly cover of fish, they communicate with the external environment. Thanks to the sensory cells of the canal walls, fish receive information about water fluctuations, navigate its currents, and determine the location of prey or dangerous objects.
Touch function performed by clusters of sensory cells (“tactile corpuscles”), scattered over the entire surface of the body. There are especially many of them concentrated near the mouth - on the antennae, lips, and also on the fins, which allows the fish to feel the touch of hard objects.
In the superficial layers of the skin there is thermoreceptors , with the help of which fish perceive temperature changes in the environment with an accuracy of 0.4 degrees. On the head of the fish there are receptors, catching changes electric and magnetic fields and, thus, promoting spatial orientation and coordination of actions of individuals of schooling fish.
A number of species have electrical organs, which are modified areas of the body’s muscles. They can be located on the head, sides and tail of fish, determining orientation towards other individuals, methods of defense and attack. They serve as receptors "neuroglandular cells" located on the body and in the lateral line channels.
Vision mainly helps fish in short-range orientation(up to 10–15 m), because due to the structure of the eye they are “myopic”: the lens is spherical, the cornea is flat, the accommodation of the eye is insignificant. However, the retina of the eyes of bony fishes contains not only sticks(black and white vision), but also cones, defining color perception. Vision is important when searching for food, protecting from danger, and intraspecific communication, especially during the breeding season.
Organ of hearing and balance presented only inner ear, which is surrounded by a cartilaginous capsule with its external ossification. The basis of the inner ear is membranous labyrinth with three semicircular canals and an oval sac, what makes up the vestibular apparatus, or organ of balance. Next to it is the actual organ of hearing - round pouch , equipped with a hollow outgrowth - lagena. The sensory cells of the lagena and saccules serve as sound receptors. Inside the sacs and lagena lie auditory pebbles, or otoliths, enhancing the perception of information about body position. In a number of fish, the vestibular apparatus is connected to the swim bladder, which increases sensitivity when maintaining balance.
general arrangement of internal organs .
Directly under the operculum visible four pairs gills arcs are bright red. Behind them is two chamber heart with the aortic bulb, from which it originates abdominal aorta, carrying blood to the gill apparatus. Between the gill cavity and the abdominal cavity there is thin vertical partition.
Located in the anterior part of the abdominal cavity liver, under which lies stomach with the one moving away from him intestines. At the beginning of the intestinal tube, finger-shaped pyloric growths(perch has three). Pancreas in most fish, in the form of lobules, it is located on the mesentery at the level of the stomach and the beginning of the intestine. In one of the intestinal loops there is maroon spleen(contains hematopoietic and lymphoid tissues).
Lies under the spinal column swim bladder, which represents hydrostatic organ, allowing the fish to change the position of its body in the water column. Functionally it is connected with inner ear, which allows the fish to determine external pressure and, transmitting its changes to the auditory apparatus (otoliths), maintain balance. In some fish, the swim bladder takes part in gas exchange and can contribute to the production of sounds.
Closer to the tail are the genitals - testes or ovaries. Testes smooth, milky cream color, which is why they got the name milk. Ovaries have granular structure and yellowish-orange color.
Rice. 29. External and internal structure of perch:
1 – mouth with teeth, 2 – gill cover, 3 – bony scales, 4 – homocercal caudal fin, 5 – anal fins, 6 – eyes, 8 – nostril, 9 – lateral line, 10 – anus, 11 – genital opening, 12 - excretory opening, 13 - open stomach, 14 - intestine, 15 - pyloric outgrowths, 16 - rectum, 17 - liver, 18 - gall bladder, 19 - pancreas, 20 - gills, 21 - spleen, 22 - swim bladder , 23 – kidneys, 24 – ureters, 25 – bladder, 26 – ovaries, 27 – atrium, 28 – ventricle, 29 – aortic bulb