The importance of fins in fish. Fish fins. Structure, functions. Paired limbs. Overview of the structure of paired fins in modern fish

Fish fins are paired and unpaired. The chest P (pinna pectoralis) and the abdominal V (pinna ventralis) belong to the paired ones; to unpaired - dorsal D (pinna dorsalis), anal A (pinna analis) and caudal C (pinna caudalis). The outer skeleton of the fins of bony fish consists of rays, which can be branchy And unbranched. The upper part of the branched rays is divided into separate rays and looks like a brush (branched). They are soft and located closer to the caudal end of the fin. Unbranched rays lie closer to the anterior margin of the fin and can be divided into two groups: segmented and non-segmented (spiny). Articular the rays are divided along the length into separate segments, they are soft and can bend. non-segmented- hard, with a sharp top, hard, can be smooth and serrated (Fig. 10).

Figure 10 - The rays of the fins:

1 - unbranched jointed; 2 - branched; 3 - prickly smooth; 4 - prickly serrated.

The number of branched and unbranched rays in the fins, especially in unpaired ones, is an important systematic feature. Rays are calculated, and their number is recorded. Non-segmented (prickly) are indicated by Roman numerals, branched - Arabic. Based on the calculation of the rays, a fin formula is compiled. So, pike perch has two dorsal fins. The first of them has 13-15 spiny rays (in different individuals), the second has 1-3 spines and 19-23 branched rays. The formula of the pikeperch dorsal fin is as follows: D XIII-XV, I-III 19-23. In the anal fin of pike perch, the number of spiny rays I-III, branched 11-14. The formula for the anal fin of pike perch looks like this: A II-III 11-14.

Paired fins. All real fish have these fins. Their absence, for example, in moray eels (Muraenidae) is a secondary phenomenon, the result of a late loss. Cyclostomes (Cyclostomata) do not have paired fins. This phenomenon is primary.

The pectoral fins are located behind the gill slits of fish. In sharks and sturgeons, the pectoral fins are located in a horizontal plane and are inactive. In these fish, the convex surface of the back and the flattened ventral side of the body give them a resemblance to the profile of an airplane wing and create lift when moving. Such asymmetry of the body causes the appearance of a torque that tends to turn the fish's head down. The pectoral fins and rostrum of sharks and sturgeons functionally constitute a single system: directed at a small (8-10°) angle to the movement, they create additional lift and neutralize the effect of torque (Fig. 11). If a shark has its pectoral fins removed, it will lift its head up to keep its body in a horizontal position. In sturgeons, the removal of the pectoral fins is not compensated in any way due to the poor flexibility of the body in the vertical direction, which is hindered by bugs, therefore, when the pectoral fins are amputated, the fish sinks to the bottom and cannot rise. Since the pectoral fins and rostrum in sharks and sturgeons are functionally related, a strong development of the rostrum is usually accompanied by a decrease in the size of the pectoral fins and their removal from the anterior part of the body. This is clearly seen in the hammerhead shark (Sphyrna) and the saw shark (Pristiophorus), whose rostrum is strongly developed and the pectoral fins are small, while in the sea fox (Alopiias) and the blue shark (Prionace), the pectoral fins are well developed and the rostrum is small.

Figure 11 - Scheme of vertical forces arising from the translational movement of a shark or sturgeon in the direction of the longitudinal axis of the body:

1 - center of gravity; 2 is the center of dynamic pressure; 3 is the force of the residual mass; V 0 - lifting force created by the hull; V R- lifting force created by the pectoral fins; V r is the lifting force created by the rostrum; Vv- lifting force created by the ventral fins; V With is the lift generated by the tail fin; Curved arrows show the effect of torque.

The pectoral fins of bony fish, in contrast to the fins of sharks and sturgeons, are located vertically and can row back and forth. The main function of the pectoral fins of bony fish is trolling propulsion, allowing precise maneuvering when searching for food. The pectoral fins, together with the ventral and caudal fins, allow the fish to maintain balance when immobile. The pectoral fins of stingrays, evenly fringing their body, act as the main movers when swimming.

The pectoral fins of fish are very diverse both in shape and size (Fig. 12). In flying fish, the length of the rays can be up to 81% of the body length, which allows

Figure 12 - Shapes of the pectoral fins of fish:

1 - flying fish; 2 - perch-creeper; 3 - keeled belly; 4 - bodywork; 5 - sea rooster; 6 - angler.

fish to float in the air. In freshwater fish, the keel-belly of the Characin family has enlarged pectoral fins that allow the fish to fly, reminiscent of the flight of birds. In gurnards (Trigla), the first three rays of the pectoral fins have turned into finger-like outgrowths, relying on which the fish can move along the bottom. In representatives of the order Angler-shaped (Lophiiformes), pectoral fins with fleshy bases are also adapted to moving along the ground and quickly digging into it. Movement on solid substrate with the help of pectoral fins made these fins very mobile. When moving on the ground, anglerfish can rely on both pectoral and ventral fins. In catfish of the genus Clarias and blennies of the genus Blennius, the pectoral fins serve as additional supports for serpentine body movements while moving along the bottom. The pectoral fins of jumping birds (Periophthalmidae) are arranged in a peculiar way. Their bases are equipped with special muscles that allow the fin to move forward and backward, and have a bend resembling an elbow joint; at an angle to the base is the fin itself. Inhabiting coastal shallows, jumpers with the help of pectoral fins are able not only to move on land, but also to climb up the stems of plants, using the caudal fin, with which they clasp the stem. With the help of pectoral fins, crawler fish (Anabas) also move on land. Pushing off with their tail and clinging to plant stems with their pectoral fins and gill cover spikes, these fish are able to travel from reservoir to reservoir, crawling hundreds of meters. In demersal fish such as rock perches (Serranidae), sticklebacks (Gasterosteidae), and wrasses (Labridae), pectoral fins are usually wide, rounded, and fan-shaped. When they work, undulation waves move vertically down, the fish appears to be suspended in the water column and can rise up like a helicopter. Fish of the order Pufferfish (Tetraodontiformes), sea needles (Syngnathidae) and skates (Hyppocampus), which have small gill slits (the gill cover is hidden under the skin), can make pectoral fins circular motions, creating an outflow of water from the gills. When the pectoral fins are amputated, these fish suffocate.

The pelvic fins perform mainly the function of balance and therefore, as a rule, are located near the center of gravity of the body of the fish. Their position changes with a change in the center of gravity (Fig. 13). In low-organized fish (herring-like, carp-like), the ventral fins are located on the belly behind the pectoral fins, occupying abdominal position. The center of gravity of these fish is on the belly, which is associated with a non-compact position. internal organs occupying a large cavity. In highly organized fish, the ventral fins are located in front of the body. This position of the pelvic fins is called thoracic and is characteristic mainly for most perch-like fish.

The pelvic fins can be located in front of the pectorals - on the throat. This arrangement is called jugular, and it is typical for large-headed fish with a compact arrangement of internal organs. The jugular position of the pelvic fins is characteristic of all fish of the cod-like order, as well as large-headed fish of the perch-like order: stargazers (Uranoscopidae), nototheniids (Nototheniidae), dogfish (Blenniidae), and others. Pelvic fins are absent in fish with an eel-like and ribbon-like body shape. In erroneous (Ophidioidei) fish, which have a ribbon-like eel-shaped body, the ventral fins are located on the chin and perform the function of tactile organs.

Figure 13 - The position of the pelvic fins:

1 - abdominal; 2 - thoracic; 3 - jugular.

The pelvic fins may change. With the help of them, some fish attach themselves to the ground (Fig. 14), forming either a suction funnel (gobies) or a suction disk (pinagora, slug). The ventral fins of the sticklebacks, modified into spines, have a protective function, while in triggerfishes, the ventral fins look like a prickly spike and, together with the spiny ray of the dorsal fin, are an organ of protection. In males cartilaginous fish the last rays of the ventral fins are transformed into pterygopodia - copulatory organs. In sharks and sturgeons, the ventral fins, like the pectoral ones, perform the function of bearing planes, but their role is less than the pectoral ones, since they serve to increase the lifting force.

Figure 14 - Modification of the ventral fins:

1 - suction funnel in gobies; 2 - the suction disk of a slug.

The habitat of fish is all kinds of water bodies of our planet: ponds, lakes, rivers, seas and oceans.

Fish occupy very vast territories, in any case, the area of ​​\u200b\u200bthe ocean exceeds 70% earth's surface. Add to this the fact that the deepest depressions go into the ocean depth by 11 thousand meters and it will become clear what spaces the fish own.

Life in the water is extremely diverse, which could not but affect the appearance of fish, and led to the fact that the shape of their bodies is diverse, like the underwater life itself.

On the head of the fish are gill wings, lips and mouth, nostrils and eyes. The head passes into the body very smoothly. From the gill wings to the anal fin is the body, which ends in the tail.

Fins serve as organs of movement for fish. In fact, they are skin outgrowths that rely on bony fin rays. The most important for fish is the caudal fin. On the sides of the body, in its lower part, there are paired ventral and pectoral fins, which correspond to the hind and forelimbs of vertebrates living on the ground. Paired fins can be positioned differently in different fish species. In the upper part of the body of the fish is the dorsal fin, and below, next to the tail, is the anal fin. Moreover, it is important to note that the number of anal and dorsal fins in fish can vary.

In most fish, on the sides of the body is an organ that perceives the flow of water and which is called the "lateral line". Thanks to this, even a blind fish is able to catch moving prey without bumping into obstacles. The visible part of the lateral line consists of scales with openings.

Through these openings, water penetrates into the channel stretching along the body, where it is perceived by the endings of nerve cells passing through the channel. The lateral line in fish may be continuous, intermittent, or absent altogether.

Functions of fins in fish

Thanks to the presence of fins, fish are able to move and maintain balance in the water. If the fish is deprived of fins, it will simply roll over with its belly up, since the center of gravity of the fish is located in its dorsal part.

The dorsal and anal fins provide the fish with a stable body position, and the caudal fin in almost all fish is a kind of mover.

As for the paired fins (ventral and pectoral), they mainly perform a stabilizing function, since they provide an equilibrium position of the body during the immobility of the fish. With the help of these fins, the fish can take the desired position of the body. In addition, they are the bearing planes during the movement of the fish, and perform the function of the steering wheel. As for the pectoral fins, this is a kind of small motor with which the fish moves during slow swimming. The pelvic fins are mainly used for balance.

fish body shape

Fish have a streamlined body shape. This is a consequence of her lifestyle and habitat. For example, those fish that are adapted to long and fast swimming in the water column (for example, salmon, cod, herring, mackerel or tuna) have a body shape similar to a torpedo. Predators that practice lightning-fast throws over very short distances (for example, saury, garfish, taimen or) have an arrow-shaped body shape.

Some species of fish that are adapted to a long stay on the bottom, such as flounder or stingray, have a flat body. Some types of fish even have bizarre body shapes, which can resemble a chess horse, as can be seen in, whose head is located perpendicular to the axis of the body.

The seahorse inhabits almost everything sea ​​waters Earth. Its body, like an insect, is enclosed in a shell, its tail is tenacious like that of a monkey, its eyes are able to rotate like a chameleon, and completes the picture with a bag, like the one that a kangaroo has. And although this strange fish can swim, keeping the vertical position of the body, using the vibrations of the dorsal fin for this, the swimmer from it is still useless. The seahorse uses its tubular stigma as a “hunting pipette”: when prey is shown nearby, the seahorse sharply inflates its cheeks and draws the prey into its mouth from a distance of 3-4 centimeters.

The smallest fish is the Philippine goby Pandaku. Its length is about seven millimeters. It was even such that women of fashion wore this bull in their ears, using crystal aquarium earrings for this.

But most big fish is, the body length of which is sometimes about fifteen meters.

Additional organs in fish

In fish of some species, such as catfish or carp, antennae can be seen around the mouth. These organs perform a tactile function and are also used to determine palatability food. Many deep sea fish, such as photoblepharon, anchovy, hatchetfish and have luminous organs.

On the scales of fish, you can sometimes find protective spikes, which can be located in different parts body. For example, the body of a hedgehog fish is covered with spikes almost entirely. Certain types of fish, such as wart, sea dragon and, have special attack and defense organs - poisonous glands, which are located at the base of the fin rays and the base of the spikes.

Body coverings in fish

From the outside, the skin of fish is covered with thin translucent plates - scales. The ends of the scales overlap each other, arranged like tiles. On the one hand, this provides the animal with strong protection, and on the other hand, it does not interfere with free movement in the water. Scales are formed by special skin cells. The size of the scales can be different: in it it is almost microscopic, while in the Indian barbel it is several centimeters in diameter. Scales are very diverse, both in their strength and in quantity, composition and a number of other characteristics.

Chromatophores (pigment cells) lie in the skin of fish, with the expansion of which, the pigment grains spread over a considerable space, making the color of the body brighter. If the chromatophores are reduced, then the pigment grains will accumulate in the center and most of the cell will remain uncolored, due to which the body of the fish will become paler. When pigment grains of all colors are evenly distributed inside the chromatophores, the fish has a bright color, and if they are collected in the centers of the cells, the fish will be so colorless that it may even seem transparent.

If only yellow pigment grains are distributed over the chromatophores, the fish will change its color to light yellow. All the diversity of fish coloration is determined by chromatophores. This is especially typical for tropical waters. In addition, in the skin of fish there are organs that perceive chemical composition and water temperature.

From the foregoing, it becomes clear that the skin of fish performs many functions at once, including external protection, and protection against mechanical damage, and communication with the external environment, and communication with relatives, and facilitating sliding.

The role of color in fish

Pelagic fish often have a dark back and a lighter belly, such as the abadejo, a member of the cod family. Many fish living in medium and upper layers water coloration of the upper body is much darker than the lower part. If you look at such fish from below, then its light belly will not stand out against the light background of the sky translucent through the water column, which masks the fish from those who lie in wait for it. marine predators. Similarly, when viewed from above, its dark back merges with the dark background of the seabed, which protects not only from predatory marine animals, but also from various fishing birds.

If you analyze the coloration of fish, you will notice how it is used to imitate and disguise other organisms. Thanks to this, the fish demonstrates danger or inedibility, and also gives signals to other fish. IN mating season, many species of fish tend to take on very bright colors, while at other times they try to blend in with the environment or imitate a completely different animal. Often, the shape of the fish complements this color disguise.

The internal structure of fish

The musculoskeletal system of fish, like that of land animals, consists of muscles and a skeleton. The skeleton is based on the spine and skull consisting of individual vertebrae. Each vertebra has a thickened part called the vertebral body, as well as inferior and superior arches. Together, the superior arches form a canal that houses the spinal cord, which is protected from injury by the arches. In the upper direction, long spinous processes depart from the arcs. In the trunk part, the lower arches are open. In the caudal part of the spine, the lower arches form a channel inside which blood vessels pass. The ribs adjoin the lateral processes of the vertebrae and perform a number of functions, primarily protecting the internal organs, and creating the necessary support for the muscles of the body. The most powerful muscles in fish are in the tail and back.

The fish skeleton includes bones and bony rays of both paired and unpaired fins. In unpaired fins, the skeleton consists of many elongated bones attached in the thickness of the muscles. There is a single bone in the abdominal girdle. In the free ventral fin, the skeleton consists of many long bones.

The skeleton of the head also includes a small cranium. The bones of the skull serve as protection for the brain, but most of the skeleton of the head is occupied by the bones of the upper and lower jaws, bones gill apparatus and eye sockets. Speaking about the gill apparatus, one can first of all note the gill covers of a large size. If the gill covers are slightly raised, then paired gill arches can be seen under them: left and right. Gills are located on these arcs.

As for the muscles, there are few of them in the head part; they are located for the most part in the region of the gill covers, on the back of the head and jaws.

Muscles that provide movement are attached to the skeletal bones. The main part of the muscles is evenly located in the dorsal part of the animal's body. The most developed are the muscles that move the tail.

The functions of the musculoskeletal system in the body of fish are very different. The skeleton serves as protection for the internal organs, the bony fin rays protect the fish from rivals and predators, and the entire skeleton, combined with the muscles, allows this inhabitant of the waters to move and defend themselves from collisions and shocks.

Digestive system in fish

Begins digestive system large mouth, which is located in front of the head and is armed with jaws. There are large small teeth. Behind oral cavity there is a pharyngeal cavity in which you can see the gill slits, which are separated by intergill septa, on which the gills are located. Outside, the gills are covered with gill covers. Next is the esophagus, followed by a fairly voluminous stomach. Behind it is the intestine.

The stomach and intestine, using the action of digestive juices, digest food, and gastric juice acts in the stomach, and several juices in the intestine at once, which secrete the glands of the intestinal walls, as well as the walls of the pancreas. Also involved in this process is the bile coming from the liver and gallbladder. Water and food digested in the intestines are absorbed into the blood, and undigested residues are thrown out through the anus.

A special organ that is found only in bony fish is the swim bladder, which is located under the spine in the body cavity. The swim bladder arises during embryonic development as a dorsal outgrowth of the intestinal tube. In order for the bubble to be filled with air, the newly born fry floats to the surface of the water and swallows air into its esophagus. After some time, the connection between the esophagus and the swim bladder is interrupted.

It is interesting that some fish use the swim bladder as a means by which they amplify the sounds they make. True, some fish do not have a swim bladder. Usually these are those fish that live on the bottom, as well as those that are characterized by vertical fast movements.

Thanks to the swim bladder, the fish does not sink under its own weight. This organ consists of one or two chambers and is filled with a mixture of gases, which in its composition is close to air. The volume of gases contained in the swim bladder can change when they are absorbed and released through the blood vessels of the walls of the swim bladder, as well as when air is swallowed. Thus, the specific gravity of the fish and the volume of its body can change in one direction or another. The swim bladder provides the fish with a balance between the mass of its body and the buoyancy force acting on it at a certain depth.

Gill apparatus in fish

As a skeletal support of the gill apparatus, fish are served by four pairs of gill arches located in a vertical plane, to which the gill plates are attached. They consist of fringe-like gill petals.

Inside the gill filaments are blood vessels that branch into capillaries. Gas exchange occurs through the walls of the capillaries: oxygen is absorbed from the water, and carbon dioxide is released back. Thanks to the contraction of the muscles of the pharynx, as well as due to the movements of the gill covers, water moves between the gill filaments, which have gill rakers that protect the delicate soft gills from clogging them with food particles.

The circulatory system in fish

Schematically, the circulatory system of fish can be depicted as a vicious circle consisting of vessels. The main organ of this system is a two-chambered heart, consisting of an atrium and a ventricle, which provides blood circulation throughout the body of the animal. Moving through the vessels, the blood provides gas exchange, as well as the transport nutrients in the body, and some other substances.

In fish, the circulatory system includes one circle of blood circulation. The heart sends blood to the gills, where it is enriched with oxygen. This oxygenated blood is called arterial blood, and is carried throughout the body, distributing oxygen throughout the cells. At the same time, it is saturated with carbon dioxide (in other words, it becomes venous), after which the blood returns back to the heart. It should be recalled that in all vertebrates, the vessels leaving the heart are called arteries, while those returning to it are called veins.

The excretory organs in fish are responsible for removing metabolic end products from the body, filtering the blood and removing water from the body. They are represented by paired kidneys, which are located along the spine by the ureters. Some fish have a bladder.

The kidneys remove excess fluid from the blood vessels harmful products exchange and salts. The ureters carry urine to bladder from where it strikes outward. Outside, the urinary canal opens with a hole, which is located just behind the anus.

Through these organs, the fish removes excess salts, water and metabolic products harmful to the body.

metabolism in fish

Metabolism is a set of chemical processes occurring in the body. The basis of metabolism in any organism is the construction of organic substances and their decay. When complex organic substances enter the body of fish along with food, they are converted into less complex ones during digestion, which, being absorbed into the blood, are carried through the cells of the body. There, they form the proteins, carbohydrates and fats required by the body. Of course, the energy released during breathing is expended on this. At the same time, many substances in the cells break down into urea, carbon dioxide and water. Consequently, metabolism is a combination of the process of building and disintegrating substances.

The intensity with which the metabolism in the body of a fish occurs depends on the temperature of its body. Since fish are animals with a variable body temperature, that is, cold-blooded, their body temperature is in close proximity to the ambient temperature. As a rule, the body temperature of fish does not exceed the ambient temperature by more than one degree. True, in some fish, for example, in tuna, the difference can be about ten degrees.

Nervous system of fish

The nervous system is responsible for the coordination of the work of all organs and systems of the body. It also provides the body's response to certain changes in the environment. It consists of a central nervous system(spinal cord and brain) and peripheral nervous system (branches extending from the brain and spinal cord). The fish brain consists of five sections: the anterior, which includes the visual lobes, the middle, diencephalon, cerebellum and medulla oblongata. In all active pelagic fish, the cerebellum and optic lobes are quite large because they need fine coordination and good vision. The medulla oblongata in fish passes into the spinal cord, ending in the caudal spine.

With the help of the nervous system, the body of the fish responds to irritations. These reactions are called reflexes, which can be divided into conditioned and unconditioned reflexes. The latter are also called congenital reflexes. Unconditioned reflexes in all animals belonging to the same species manifest themselves in the same way, while conditioned reflexes are individual and are developed during the life of a particular fish.

Sense organs in fish

The sense organs of fish are very well developed. The eyes are able to clearly recognize objects at close range and distinguish colors. The sounds of fish are perceived through the inner ear located inside the skull, and smells are recognized through the nostrils. In the oral cavity, the skin of the lips and antennae, there are taste organs that allow fish to distinguish between salty, sour and sweet. The lateral line, due to the sensitive cells located in it, is sensitive to changes in water pressure and transmits the corresponding signals to the brain.

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All fins in fish are divided into paired, which correspond to the limbs of higher vertebrates, as well as unpaired. Paired fins include pectoral (P - pinna pectoralis) and ventral (V - pinna ventralis). Unpaired fins include dorsal (D - p. dorsalis); anal (A - p. analis) and tail (C - p. caudalis).

A number of fish (salmon, characin, orcas, etc.) have an adipose fin behind the dorsal fin, it is devoid of fin rays (p.adiposa).

Pectoral fins are common in bony fish, while moray eels and some others lack them. Lampreys and hagfish are completely devoid of pectoral and ventral fins. In stingrays, the pectoral fins are greatly enlarged and play the main role as organs of their movement. Especially strong pectoral fins have developed in flying fish. The three rays of the pectoral fin in the gurnard act as legs when crawling on the ground.

The pelvic fins may be different position. Abdominal position - they are located approximately in the middle of the abdomen (sharks, herring-like, cyprinids). In the thoracic position, they are shifted to the front of the body (perciformes). Jugular position, fins located in front of the pectorals and on the throat (cod).

In some fish, the ventral fins are turned into spines (stickleback) or into a sucker (pinogora). In male sharks and rays, the posterior rays of the ventral fins have evolved into copulatory organs. They are completely absent in eels, catfish, etc.

May be different quantity dorsal fins. In herring and cypriniforms, it is one, mullet and perch - two, in cod - three. Their location may be different. In pike, it is shifted far back, in herring-like, cyprinids - in the middle of the body, in perch and cod - closer to the head. The longest and highest dorsal fin in sailboat fish. In flounder, it looks like a long ribbon running along the entire back and at the same time with almost the same anal fin, it is their main organ of movement. Mackerel, tuna and saury have small additional fins behind the dorsal and anal fins.

Separate rays of the dorsal fin sometimes extend into long filaments, and in monkfish the first ray of the dorsal fin is shifted to the muzzle and transformed into a kind of fishing rod, like in deep sea anglerfish. The first dorsal fin of the sticky fish also shifted to the head and turned into a real sucker. The dorsal fin in sedentary demersal fish species is poorly developed (catfish) or absent (stingrays, electric eel) .

Tail fin:
1) isobathic - the upper and lower lobes are the same (tuna, mackerel);
2) hypobatic - the lower lobe is elongated (flying fish);
3) epibate - the upper lobe is elongated (sharks, sturgeons).

Types of caudal fins: forked (herring), notched (salmon), truncated (cod), rounded (burbot, gobies), semilunar (tuna, mackerel), pointed (eelpout).

The function of movement and balance has been assigned to the fins from the very beginning, but sometimes they perform other functions. The main fins are dorsal, caudal, anal, two ventral and two pectoral. They are divided into unpaired - dorsal, anal and caudal, and paired - thoracic and abdominal. Some species also have an adipose fin located between the dorsal and caudal fins. All fins are driven by muscles. In many species, the fins are often modified. So, in males of viviparous fish, the modified anal fin has turned into a mating organ; in some species, the pectoral fins are well developed, which allows the fish to jump out of the water. Gourami have special tentacles, which are thread-like pelvic fins. And in some species that burrow into the ground, fins are often absent. The tail fins of guppies are also an interesting creation of nature (there are about 15 species and their number is growing all the time). The movement of the fish is started by the tail and caudal fin, which send the body of the fish forward with a strong blow. The dorsal and anal fins provide balance to the body. The pectoral fins move the body of the fish during slow swimming, serve as a rudder and, together with the ventral and caudal fins, ensure the equilibrium position of the body when it is real. In addition, some species of fish can rely on pectoral fins or move with their help on a hard surface. The pelvic fins perform mainly the function of balance, but in some species they are changed into a suction disk, which allows the fish to stick to a hard surface.

1. Dorsal fin.

2. Adipose fin.

3. Caudal fin.

4. pectoral fin.

5. Pelvic fin.

6. Anal fin.

The structure of the fish. Types of tail fins:

Truncated

Split

lyre-shaped

24. The structure of the skin of fish. The structure of the main types of fish scales, its functions.

The skin of fish performs a number of important functions. Located on the border of the outer and internal environment organism, it protects the fish from external influences. At the same time, separating the body of the fish from the surrounding liquid medium with dissolved in it chemicals, fish skin is an effective homeostatic mechanism.

Fish skin regenerates quickly. Through the skin, on the one hand, a partial release of the end products of metabolism occurs, and on the other, the absorption of certain substances from external environment(oxygen, carbonic acid, water, sulfur, phosphorus, calcium and other elements that play an important role in life). The skin as a receptor surface plays an important role: thermo-, baro-chemo- and other receptors are located in it. In the thickness of the corium, the integumentary bones of the skull and pectoral fin belts are formed.

In fish, the skin also performs a rather specific - supporting - function. On inside the skin is fixed muscle fibers of skeletal muscles. Thus, it acts as a supporting element in the composition of the musculoskeletal system.

Fish skin consists of two layers: outer layer epithelial cells, or epidermis, and the inner layer of connective tissue cells - the actual skin, dermis, corium, cutis. Between them, a basement membrane is isolated. The skin is underlain by a loose connective tissue layer (subcutaneous connective tissue, subcutaneous tissue). In many fish, fat is deposited in the subcutaneous tissue.

The epidermis of fish skin is represented by a stratified epithelium consisting of 2–15 rows of cells. The cells of the upper layer of the epidermis are flat. The lower (growth) layer is represented by one row of cylindrical cells, which, in turn, originate from the prismatic cells of the basement membrane. The middle layer of the epidermis consists of several rows of cells, the shape of which varies from cylindrical to flat.

The outermost layer of epithelial cells becomes keratinized, but unlike terrestrial vertebrates in fish, it does not die off, retaining its connection with living cells. During the life of the fish, the intensity of keratinization of the epidermis does not remain unchanged, it reaches its greatest extent in some fish before spawning: for example, in males of cyprinids and whitefishes, in some places of the body (especially on the head, gill covers, sides, etc.) the so-called pearl rash - a mass of small white bumps that roughen the skin. After spawning, she disappears.

The dermis (cutis) consists of three layers: a thin upper (connective tissue), a thick middle mesh layer of collagen and elastin fibers and a thin basal layer of high prismatic cells, giving rise to the two upper layers.

In active pelagic fish, the dermis is well developed. Its thickness in areas of the body that provide intensive movement (for example, on the caudal peduncle of a shark) is greatly increased. The middle layer of the dermis in active swimmers can be represented by several rows of strong collagen fibers, which are also interconnected by transverse fibers.

In slow-swimming littoral and bottom fish, the dermis is loose or generally underdeveloped. In fast-swimming fish, in areas of the body that provide swimming (for example, the caudal peduncle), subcutaneous tissue is absent. In these places, muscle fibers are attached to the dermis. In other fish (most often slow ones), subcutaneous tissue is well developed.

The structure of fish scales:

Placoid (it is very ancient);

ganoid;

Cycloid;

Ctenoid (the youngest).

placoid fish scale

placoid fish scale(photo above) is characteristic of modern and fossil cartilaginous fish - and these are sharks and rays. Each such scale has a plate and a spike sitting on it, the tip of which goes out through the epidermis. In this scale, the basis is dentin. The spike itself is covered with even harder enamel. The placoid scale inside has a cavity that is filled with pulp - pulp, it has blood vessels and nerve endings.

Ganoid fish scale

Ganoid fish scale has the form of a rhombic plate and the scales are connected to each other, forming a dense shell on the fish. Each such scale is made of a very hard substance - the upper part is made of ganoin, and the lower part is made of bone. This type of scales have a large number of fossil fish, as well as the upper parts in the caudal fin in modern sturgeons.

Cycloid fish scale

Cycloid fish scale found in bony fish and does not have a layer of ganoin.

Cycloid scales have a rounded neck with a smooth surface.

Ctenoid fish scale

Ctenoid fish scale also found in bony fish and does not have a layer of ganoin, on back side she has thorns. Usually the scales of these fish are tiled, and each scale is covered in front and on both sides by the same scales. It turns out that the back end of the scale comes out, but it is also lined with another scale from below, and this type of cover retains the flexibility and mobility of the fish. Annual rings on the scales of fish allow you to determine its age.

The arrangement of scales on the body of the fish goes in rows and the number of rows and the number of scales in the longitudinal row do not change with the age of the fish, which is an important systematic feature for different species. Let's take this example - the lateral line of goldfish has 32-36 scales, while the pike has 111-148.

; their organs that regulate movement and position in the water, and in some ( flying fish) - also planning in the air.

The fins are cartilaginous or bony rays (radials) with skin-epidermal integuments on top.

The main types of fish fins are dorsal, anal, caudal, a pair of abdominal and a pair of thoracic.
Some fish also have adipose fins(they lack fin rays) located between the dorsal and caudal fins.
The fins are driven by muscles.

Often, in different species of fish, the fins are modified, for example, males viviparous fish they use the anal fin as an organ for mating (the main function of the anal fin is similar to the function of the dorsal fin - this is the keel when the fish moves); at gourami modified filiform ventral fins are special tentacles; strongly developed pectoral fins allow some fish to jump out of the water.

The fins of the fish are actively involved in the movement, balancing the body of the fish in the water. In this case, the motor moment begins from the caudal fin, which pushes forward with a sharp movement. The tail fin is a kind of fish mover. The dorsal and anal fins balance the body of the fish in the water.

Different types of fish have different numbers of dorsal fins.
Herring and cyprinids have one dorsal fin mullets and perciformes- two, at cod-like- three.
They can also be located in different ways: pike- shifted far back herring, cyprinids- in the middle of the ridge perch and cod- closer to the head. At mackerel, tuna and saury there are small additional fins behind the dorsal and anal fins.

The pectoral fins are used by fish when swimming slowly, and together with the ventral and caudal fins, they maintain the balance of the fish's body in the water. Many bottom fish move on the ground with the help of pectoral fins.
However, some fish moray, for example) pectoral and ventral fins are absent. Some species also lack a tail: hymnots, ramphichts, seahorses, stingrays, moonfish and other species.

Three-spined stickleback

In general, the more developed the fins of a fish, the more adapted it is to swimming in calm water.

In addition to movement in water, air, on the ground; jumps, jumps, fins help different types fish to attach to the substrate (fins-suckers in bychkov), look for food ( trigles), have protective functions ( stickleback).
Some types of fish scorpionfish) at the bases of the spines of the dorsal fin have poisonous glands. There are also fish without fins at all: cyclostomes.

cartilaginous fish .

Paired fins: The shoulder girdle looks like a cartilaginous semicircle lying in the muscles of the body walls behind the branchial region. On its lateral surface on each side there are articular outgrowths. The part of the girdle lying dorsal to this outgrowth is called scapular department, ventral - coracoid department. At the base of the skeleton of the free limb (pectoral fin) there are three flattened basal cartilages attached to the articular outgrowth of the shoulder girdle. Distal to the basal cartilages are three rows of rod-shaped radial cartilages. The rest of the free fin is his skin lobe– supported by numerous thin elastin threads.

Pelvic girdle represented by a transversely elongated cartilaginous plate lying in the thickness of the abdominal muscles in front of the cloacal fissure. The skeleton of the pelvic fins is attached to its ends. IN pelvic fins there is only one base element. It is greatly elongated and one row of radial cartilages is attached to it. The rest of the free fin is supported by elastic threads. In males, the elongated basal element extends beyond the fin lobe as the skeletal base of the copulatory outgrowth.

Unpaired fins: As a rule, they are represented by a caudal, anal, and two dorsal fins. The tail fin of sharks is heterocercal, i.e. its upper lobe is much longer than the lower one. It enters the axial skeleton - the spine. The skeletal base of the caudal fin is formed by elongated upper and lower vertebral arches and a row of radial cartilages attached to the upper arches of the caudal vertebrae. Most of the tail blade is supported by elastic threads. At the base of the skeleton of the dorsal and anal fins lie radial cartilages, which are immersed in the thickness of the muscles. The free blade of the fin is supported by elastic threads.

Bony fish.

Paired fins. Represented by pectoral and ventral fins. The shoulder girdle serves as a support for the chest. The pectoral fin at its base has one row of small bones - radial extending from the scapula (component of the shoulder girdle). The skeleton of the entire free blade of the fin consists of segmented skin rays. The difference from cartilage is the reduction of basals. The mobility of the fins is increased, since the muscles are attached to the expanded bases of the skin rays, which flexibly articulate with the radials. The pelvic girdle is represented by closely interlocking paired flat triangular bones that lie in the thickness of the muscles and are not connected with the axial skeleton. Most of the pelvic fins, which are bony in the skeleton, lack basals and have reduced radials; the lobe is supported only by skin rays, the expanded bases of which are directly attached to the pelvic girdle.

Unpaired limbs. Represented by dorsal, anal (undercaudal) and caudal fins. Anal and dorsal fins consist of bone rays, subdivided into internal (hidden in the thickness of the muscles) pterygiophores(corresponding to the radials) and outer fin rays - lepidotrichia. tail fin asymmetrical. In it, the continuation of the spine - urostyle, and behind and below it with a fan are flat triangular bones - hypuralia, derivatives of the lower arches of underdeveloped vertebrae. This type of fin structure is externally symmetrical, but not internally - homocercal. The outer skeleton of the caudal fin is composed of numerous skin rays - lepidotrichia.

There is a difference in the location of the fins in space - in cartilaginous horizontally to maintain in water, and in teleosts vertically because they have a swim bladder. Fins during movement perform various functions:

• unpaired - dorsal, caudal and anal fins, located in the same plane, help the movement of the fish;
• paired - pectoral and ventral fins - maintain balance, and also serve as a rudder and brake.