The value of the dorsal fin in fish. Fins and types of movement of fish. The internal structure of fish

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, killer whale, 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 can take a 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.

There may be a different number of 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 stretch into long threads, and in the anglerfish the first ray of the dorsal fin is shifted to the muzzle and transformed into a kind of fishing rod, like in the 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 external and internal environment of the body, it protects the fish from external influences. At the same time, by separating the fish body from the surrounding liquid medium with chemicals dissolved in it, the 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 hand, the absorption of certain substances from the 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. Muscle fibers of skeletal muscles are fixed on the inner side of the skin. Thus, it acts as a supporting element in the composition of the musculoskeletal system.

The skin of fish consists of two layers: the outer layer of epithelial cells, or epidermis, and the inner layer of connective tissue cells - the skin proper, 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 male 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, it has spikes on the back. 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.

Material and equipment. A set of fixed fish - 30-40 species. Tables: Position of pelvic fins; Fin modifications; Tail fin types; diagram of the position of the caudal fin of various shapes relative to the zone of vortices. Tools: dissecting needles, tweezers, bath (one set for 2-3 students).

Exercise. When performing work, it is necessary to consider on all types of fish of the set: paired and unpaired fins, branched and unbranched, as well as segmented and non-segmented rays of the fins, the position of the pectoral fins and three positions of the pelvic fins. Find fish that do not have paired fins; with modified paired fins; with one, two and three dorsal fins; with one and two anal fins, as well as fish without an anal fin; with modified unpaired fins. Identify all types and shapes of the caudal fin.

Compile formulas for the dorsal and anal fins for the fish species indicated by the teacher, and list the fish species in the set with different shapes of the caudal fin.

Draw branched and unbranched, segmented and non-segmented rays of the fins; fish with three positions of ventral fins; tail fins of fish of various shapes.

Fish fins are paired and unpaired. To paired belong thoracic P (pinnapectoralis) and abdominal V (pinnaventralis); to unpaired - dorsal D (pinnadorsalis), anal A (pinnaanalis) and caudal C (pinnacaudalis). 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: DXIII-XV,I-III19-23. 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: AII-III11-14.

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 sturgeon fish, 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.

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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; V v- 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

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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, enlarged pectoral fins, 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, 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 circular movements with their pectoral fins, 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 located on the belly, which is associated with the non-compact position of the 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.

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Figure 13 - Position of the ventral 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 pelvic fins of the sticklebacks, modified into spines, have a protective function, while in triggerfishes, the pelvic fins look like a prickly spike and, together with the spiny ray of the dorsal fin, are an organ of protection. In male 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.

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Figure 14 - Modification of the pelvic fins:

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

Unpaired fins. As noted above, unpaired fins include dorsal, anal and caudal.

The dorsal and anal fins act as stabilizers and resist lateral displacement of the body when the tail is working.

The large dorsal fin of sailboats acts like a rudder during sharp turns, greatly increasing the maneuverability of the fish when chasing prey. The dorsal and anal fins in some fishes act as movers, imparting translational movement to the fish (Fig. 15).

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Figure 15 - The shape of undulating fins in various fish:

1 - sea Horse; 2 - sunflower; 3 - moon fish; 4 - bodywork; 5 - sea needle; 6 - flounder; 7 - electric eel.

Locomotion with the help of undulating movements of the fins is based on wave-like movements of the fin plate, due to successive transverse deflections of the rays. This method of movement is usually characteristic of fish with a small body length, unable to bend the body - boxfish, moonfish. Only due to the undulation of the dorsal fin do seahorses and sea needles move. Such fish as flounder and sunfish, along with undulating movements of the dorsal and anal fins, swim by bending the body laterally.

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Figure 16 - Topography of the passive locomotor function of unpaired fins in various fish:

1 - eel; 2 - cod; 3 - horse mackerel; 4 - tuna.

In slow-swimming fish with an eel-shaped body, the dorsal and anal fins, merging with the caudal, form a single fin fringing the body in a functional sense, and have a passive locomotor function, since the main work falls on the body body. In fast-moving fish, with an increase in the speed of movement, the locomotor function is concentrated in the posterior part of the body and on the posterior parts of the dorsal and anal fins. An increase in speed leads to the loss of the locomotor function of the dorsal and anal fins, the reduction of their posterior sections, while the anterior sections perform functions that are not related to locomotion (Fig. 16).

In fast-swimming scombroid fish, the dorsal fin, when moving, fits into a groove running along the back.

Herring, garfish and other fish have one dorsal fin. Highly organized orders of bony fish (perch-like, mullet-like), as a rule, have two dorsal fins. The first consists of prickly rays, which give it a certain lateral stability. These fish are called spiny fish. Codfish have three dorsal fins. Most fish have only one anal fin, while cod-like fish have two.

Dorsal and anal fins are absent in a number of fish. For example, the electric eel does not have a dorsal fin, the locomotor undulating apparatus of which is a highly developed anal fin; the stingrays do not have it either. The stingrays and sharks of the order Squaliformes do not have anal fins.

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Figure 17 - Modified first dorsal fin in a stick fish ( 1 ) and anglerfish ( 2 ).

The dorsal fin may change (Fig. 17). So, in a sticky fish, the first dorsal fin moved to the head and turned into a suction disk. It is, as it were, divided by partitions into a number of independently acting smaller, and therefore relatively more powerful suckers. The septa are homologous to the rays of the first dorsal fin, they can be bent back, taking an almost horizontal position, or straightened. Due to their movement, a suction effect is created. In anglerfish, the first rays of the first dorsal fin, separated from each other, turned into a fishing rod (ilicium). In sticklebacks, the dorsal fin has the form of isolated spines that perform a protective function. In trigger fish of the genus Balistes, the first ray of the dorsal fin has a locking system. It straightens and is fixed motionless. You can get it out of this position by pressing the third spiny ray of the dorsal fin. With the help of this ray and the spiny rays of the ventral fins, the fish, in case of danger, hides in crevices, fixing the body in the floor and ceiling of the shelter.

In some sharks, the elongated back lobes of the dorsal fins create a certain amount of lift. A similar, but more significant, supportive force is provided by the long-based anal fin, such as in catfish.

The caudal fin acts as the main mover, especially in the scombroid type of movement, being the force that tells the fish to move forward. It provides high maneuverability of fish when turning. There are several forms of the caudal fin (Fig. 18).

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Figure 18 - Shapes of the caudal fin:

1 – protocirkal; 2 - heterocercal; 3 - homocercal; 4 - diphycercal.

Protocercal, i.e., initially equally lobed, has the appearance of a border, supported by thin cartilaginous rays. The end of the chord enters the central part and divides the fin into two equal halves. This is the oldest type of fin, characteristic of cyclostomes and larval stages of fish.

Diphycercal - symmetrical externally and internally. The spine is located in the middle of equal lobes. It is inherent in some lungfish and crossopterans. Of the bony fish, such a fin is found in garfish and cod.

Heterocercal, or asymmetrical, unequal. The upper lobe expands, and the end of the spine, curving, enters it. This type of fin is characteristic of many cartilaginous fishes and cartilaginous ganoids.

Homocercal, or falsely symmetrical. This fin can be outwardly attributed to equal lobes, but the axial skeleton is distributed unevenly in the lobes: the last vertebra (urostyle) extends into the upper lobe. This type of fin is widespread and common to most bony fish.

According to the ratio of the sizes of the upper and lower lobes, the caudal fins can be epi-,hypo- and isobathic(cercal). In the epibatic (epcercal) type, the upper lobe is longer (sharks, sturgeons); with hypobatic (hypocercal) the upper lobe is shorter (flying fish, sabrefish), with isobathic (isocercal) both lobes have the same length (herring, tuna) (Fig. 19). The division of the caudal fin into two lobes is associated with the peculiarities of the flow around the body of the fish by counter currents of water. It is known that a friction layer is formed around a moving fish - a layer of water, to which a certain additional speed is imparted by the moving body. With the development of fish speed, separation of the boundary layer of water from the surface of the body of the fish and the formation of a zone of eddies are possible. With a symmetrical (relative to its longitudinal axis) fish body, the zone of vortices that arises behind is more or less symmetrical about this axis. At the same time, to exit the zone of vortices and the friction layer, the caudal fin blades lengthen in equal measure - isobathism, isocercia (see Fig. 19, a). With an asymmetric body: a convex back and a flattened ventral side (sharks, sturgeons), the vortex zone and the friction layer are shifted upward relative to the longitudinal axis of the body, therefore, the upper lobe elongates to a greater extent - epibatism, epicercia (see Fig. 19, b). If the fish have a more convex ventral and straight dorsal surfaces (sabrefish), the lower lobe of the caudal fin lengthens, since the zone of vortices and the friction layer are more developed on the underside of the body - hypobatism, hypocercia (see Fig. 19, c). The higher the speed of movement, the more intense the process of vortex formation and the thicker the friction layer and the more developed the blades of the caudal fin, the ends of which should go beyond the zone of vortices and the friction layer, which ensures high speeds. In fast-swimming fish, the caudal fin has either a semi-lunar shape - short with well-developed sickle-shaped elongated lobes (scombroid), or forked - the notch of the tail goes almost to the base of the body of the fish (scad, herring). In sedentary fish, with slow movement of which the processes of vortex formation almost do not take place, the lobes of the caudal fin are usually short - a notched caudal fin (carp, perch) or not differentiated at all - rounded (burbot), truncated (sunflowers, butterfly fish), pointed ( captain's croakers).

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Figure 19 - Scheme of the location of the blades of the caudal fin relative to the zone of vortices and the friction layer for different body shapes:

a- with a symmetrical profile (isocercia); b- with a more convex profile contour (epicercium); in- with a more convex lower profile contour (hypocercia). The vortex zone and the friction layer are shaded.

The size of the tail fin lobes is usually related to the height of the fish's body. The higher the body, the longer the blades of the caudal fin.

In addition to the main fins, there may be additional fins on the body of the fish. These include fatty fin (pinnaadiposa), located behind the dorsal fin above the anal and representing a fold of skin without rays. It is typical for fish of the salmon, smelt, grayling, kharacin and some catfish families. On the caudal peduncle of a number of fast-swimming fish, behind the dorsal and anal fins, there are often small fins consisting of several rays.

R Figure 20 - Keels on the caudal peduncle in fish:

a- in the herring shark; b- mackerel.

They act as dampeners for eddies formed during the movement of fish, which contributes to an increase in the speed of fish (combroid, mackerel). On the caudal fin of herring and sardines are elongated scales (alae), which act as fairings. On the sides of the caudal peduncle in sharks, horse mackerel, mackerel, swordfish, there are lateral keels, which help to reduce the lateral bending of the caudal peduncle, which improves the locomotor function of the caudal fin. In addition, the lateral keels serve as horizontal stabilizers and reduce the formation of eddies when the fish swims (Fig. 20).

Questions for self-examination:

What fins are included in the group of paired, unpaired? Give their Latin designations.

What fish have an adipose fin?

What types of fin rays can be distinguished and how do they differ?

Where are the pectoral fins of fish located?

Where are the ventral fins of fish located and what determines their position?

Give examples of fish with modified pectoral, ventral, and dorsal fins.

Which fish do not have pelvic and pectoral fins?

What are the functions of paired fins?

What role do the dorsal and anal fins play?

What types of structure of the caudal fin are distinguished in fish?

What are epibatic, hyobatic, isobathic caudal fins?

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. AT 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 musculature 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.

Fins

organs of movement of aquatic animals. Among invertebrates, P. have pelagic forms of gastropods and cephalopods and setae-jaws. In gastropod mollusks, the p. is a modified leg; in cephalopods, lateral skin folds. The chaetognaths are characterized by lateral and caudal P., formed by skin folds. Among modern vertebrates, P. have cyclostomes, fish, some amphibians, and mammals. In cyclostomes, only unpaired P.: anterior and posterior dorsal (in lampreys) and caudal.

In fish, paired and unpaired P. are distinguished. Paired are represented by anterior (thoracic) and posterior (abdominal). In some fish, such as cod and blennies, the ventral P. are sometimes located in front of the pectorals. The skeleton of paired P. consists of cartilaginous or bone rays, which are attached to the skeleton of the limb belts (See. Limb belts) (rice. one ). The main function of paired P. is the direction of movement of fish in a vertical plane (rudders of depth). In a number of fish, the paired P. function as organs of active swimming. Swimming) or serve for gliding in the air (for flying fish), crawling along the bottom or moving on land (for fish that periodically emerge from the water, for example, representatives of the tropical genus Periophtalmus, which can even climb trees with the help of chest P.). The skeleton of unpaired P. - dorsal (often divided into 2, and sometimes into 3 parts), anal (sometimes divided into 2 parts) and caudal - consists of cartilaginous or bone rays lying between the lateral muscles of the body ( rice. 2 ). The skeletal rays of the caudal P. are connected with the posterior end of the spine (in some fish they are replaced by spinous processes of the vertebrae).

Peripheral parts of P. are supported by thin beams from horn-shaped or bone tissue. In spiny-finned fish, the anterior of these rays thicken and form hard spines, sometimes associated with poisonous glands. Muscles are attached to the base of these rays, which stretch the lobe of the pelvis. The dorsal and anal pelvis serve to regulate the direction of movement of the fish, but sometimes they can also be organs of translational movement or perform additional functions (for example, attracting prey). The caudal P., which varies greatly in shape in different fish, is the main organ of locomotion.

In the course of the evolution of vertebrates, P. fishes probably originated from a continuous skin fold that ran along the back of the animal, went around the posterior end of its body and continued on the ventral side to the anus, then divided into two lateral folds that continued to the gill slits; this is the position of the fin folds in the modern primitive chordate - Lancelet a. It can be assumed that during the evolution of animals, skeletal elements were formed in some places of such folds and the folds disappeared in the intervals, which led to the emergence of unpaired P. in cyclostomes and fish and paired ones in fish. This is supported by the finding of lateral folds or venom of spines in the most ancient vertebrates (certain jawless animals and acanthodia) and by the fact that in modern fish the paired spines are longer in the early stages of development than in the adult state. Among amphibians, unpaired pimples in the form of a skin fold lacking a skeleton are present as permanent or temporary formations in most larvae living in water, as well as in adult caudate and larvae of anurans. Among mammals, P. are found in cetaceans and lilacs that have switched to an aquatic lifestyle for the second time. Unpaired P. cetaceans (vertical dorsal and horizontal tail) and lilac (horizontal tail) do not have a skeleton; these are secondary formations, not homologous (see. Homology) unpaired P. fish. The paired P. of cetaceans and lilacs, represented only by the anterior P. (the posterior ones are reduced), have an internal skeleton and are homologous to the forelimbs of all other vertebrates.

Lit. Guide to Zoology, vol. 2, M.-L., 1940; Shmalgauzen II, Fundamentals of Comparative Anatomy of Vertebrate Animals, 4th ed., M., 1947; Suvorov E.K., Fundamentals of Ichthyology, 2nd ed., M., 1947; Dogel V. A., Zoology of invertebrates, 5th ed., M., 1959; Aleev Yu. G., Functional foundations of the external structure of fish, M., 1963.

V. N. NIKITIN.

Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

See what "Fins" are in other dictionaries:

- (pterigiae, pinnae), organs of movement or regulation of the position of the body of aquatic animals. Among the invertebrates, P. has a pelagic. forms of certain mollusks (a modified leg or a fold of skin), chaetognaths. In non-cranial and larvae of fish, unpaired P. ... ... Biological encyclopedic dictionary

Organs of movement or regulation of the position of the body of aquatic animals (some mollusks, chaetognaths, lancelets, cyclostomes, fish, some amphibians and mammals, cetaceans and sirens). They can be paired and unpaired. * * * FINS… … encyclopedic Dictionary

Organs of movement or regulation of the position of the body of aquatic animals (some molluscs, chaetognaths, lancelet, cyclostomes, fish, some amphibians and mammals, cetaceans and sirenians). Distinguish between paired and unpaired fins... Big Encyclopedic Dictionary