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The pectoral and ventral fins of fish are paired. Fish fins. Structure, functions. Paired limbs. Review of the structure of paired fins in modern fish

The unpaired fins include the dorsal, anal and caudal fins.

The dorsal and anal fins act as stabilizers and resist lateral displacement of the body during tail action.

The large dorsal fin of sailfish acts as a rudder during sharp turns, greatly increasing the maneuverability of the fish when pursuing prey. The dorsal and anal fins of some fish act as propellers, imparting forward movement to the fish (Fig. 15).

Figure 15 – Shape of undulating fins in various fish:

1 - sea Horse; 2 – sunflower; 3 – moon fish; 4 – body; 5 – needlefish; 6 – flounder; 7 - electric eel.

Locomotion with the help of undulating movements of the fins is based on the wave-like movements of the fin plate, caused by successive transverse deflections of the rays. This method of movement is usually characteristic of fish with a short body length that are unable to bend the body - boxfishes, sunfish. They move only due to undulation of the dorsal fin. Sea Horses And pipefish. Fishes such as flounders and sunfishes, along with the undulating movements of the dorsal and anal fins, swim by laterally curving their body.

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-like body shape, the dorsal and anal fins, merging with the caudal fin, form in a functional sense a single fin bordering the body and have a passive locomotor function, since the main work falls on the body body. In fast-moving fish, as the speed of movement increases, 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 locomotor function by the dorsal and anal fins, reduction of their posterior sections, while the anterior sections perform functions not related to locomotion (Fig. 16).

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

Herring, garfish and other fish have one dorsal fin. In highly organized units bony fish(perch-like, mullet-like) usually have two dorsal fins. The first consists of spiny rays, which give it a certain lateral stability. These fish are called spiny-finned fish. Gadfish have three dorsal fins. Most fish have only one anal fin, but cod-like fish have two.

Some fish lack dorsal and anal fins. For example, there is no dorsal fin electric eel, the locomotor undulating apparatus of which is a highly developed anal fin; Stingrays do not have it either. Stingrays and sharks of the order Squaliformes do not have an anal fin.

Figure 17 – Modified first dorsal fin of the sticky fish ( 1 ) and anglerfish ( 2 ).

The dorsal fin can be modified (Fig. 17). Thus, in the 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, suction cups. The septa are homologous to the rays of the first dorsal fin; they can bend back, taking an almost horizontal position, or straighten. 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 looks like isolated spines that perform protective function. In triggerfish of the genus Balistes, the first ray of the dorsal fin has a locking system. It straightens and is fixed motionless. You can remove it from 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, when in danger, hides in crevices, fixing the body in the floor and ceiling of the shelter.

In some sharks, the rear elongated lobes of the dorsal fins create a certain lifting force. A similar, but more significant, supporting force is created by the anal fin with a long base, for example, in catfishes.

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

Figure 18 – Shapes of the caudal fin:

1 – protocentral; 2 – heterocercal; 3 – homocercal; 4 – diphycercal.

Protocercal, i.e., primarily equilobed, has the appearance of a border, and is supported by thin cartilaginous rays. The end of the chord enters central part and divides the fin into two equal halves. This is the most ancient type fin, characteristic of cyclostome and larval stages of fish.

Diphycercal – symmetrical externally and internally. The spine is located in the middle of equal blades. It is characteristic of some lungfishes and lobe-finned fishes. Of the bony fishes, garfish and cod have such a fin.

Heterocercal, or asymmetrical, unequally lobed. The upper blade expands, and the end of the spine, bending, enters it. This type of fin is characteristic of many cartilaginous fishes and cartilaginous ganoids.

Homocercal, or falsely symmetrical. This fin can be externally classified as equilobed, but the axial skeleton is distributed unequally in the blades: the last vertebra (urostyle) extends into the upper blade. This type of fin is widespread and characteristic of most bony fish.

According to the ratio of the sizes of the upper and lower blades, the caudal fins can be epi-, hypo- And isobathic(ecclesiastical). With the epibate (epicercal) type, the upper lobe is longer (sharks, sturgeons); with hypobate (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 blades is associated with the peculiarities of counter currents of water flowing around the body of the fish. 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. As the fish develops speed, the boundary layer of water may separate from the surface of the fish's body and a zone of vortices may form. If the body of the fish is symmetrical (relative to its longitudinal axis), the zone of vortices that arises behind is more or less symmetrical relative to this axis. In this case, to exit the zone of vortices and the friction layer, the blades of the caudal fin lengthen equally - isobathism, isocercia (see Fig. 19, a). With an asymmetrical 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 - epibathicity, epicercia (see Fig. 19, b). If fish have a more convex ventral and straight dorsal surface (siberian fish), the lower lobe of the caudal fin lengthens, since the vortex zone and the friction layer are more developed on the lower side of the body - hypobate, hypocercion (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 extend beyond the boundaries of the vortex zone and the friction layer, which ensures high speeds. In fast-swimming fish, the caudal fin has either a semilunar shape - short with well-developed sickle-shaped elongated blades (scombroids), or forked - the notch of the tail goes almost to the base of the fish's body (horse mackerel, herring). In sedentary fish, during the slow movement of which the processes of vortex formation almost do not take place, the blades of the caudal fin are usually short - a notched caudal fin (carp, perch) or not differentiated at all - rounded (burbot), truncated (sunfish, butterfly fish), pointed ( captain's croakers).

Figure 19 – Layout of the caudal fin blades relative to the vortex zone and friction layer at different shapes body:

A– with a symmetrical profile (isocercia); b– with a more convex profile contour (epicerkia); V– with a more convex lower contour of the profile (hypocercia). The vortex zone and friction layer are shaded.

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

In addition to the main fins, fish may have additional fins on their body. These include fatty fin (pinna adiposa), located behind the dorsal fin above the anal fin and representing a fold of skin without rays. It is typical for fish of the Salmon, Smelt, Grayling, Characin 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.

Figure 20 – Keels on the caudal peduncle of fish:

A– in the herring shark; b- in mackerel.

They act as dampers for turbulence generated during the movement of fish, which helps to increase the speed of fish (scombroid, mackerel). On the caudal fin of herrings and sardines there are elongated scales (alae), which act as fairings. On the sides of the caudal peduncle in sharks, horse mackerel, mackerel, and swordfish there are lateral keels, which help reduce the lateral bendability of the caudal peduncle, which improves the locomotor function of the caudal fin. In addition, the side keels serve as horizontal stabilizers and reduce vortex formation when the fish swims (Fig. 20).

Fish fins can be paired or unpaired. The paired ones include the thoracic P (pinna pectoralis) and the abdominal V (pinna ventralis); to the unpaired ones - dorsal D (pinna dorsalis), anal A (pinna analis) and caudal C (pinna caudalis). The exoskeleton of the fins of bony fishes consists of rays that can be branchy And unbranched. Top part branched rays is divided into separate rays and has the appearance of a brush (branched). They are soft and located closer to the caudal end of the fin. Unbranched rays lie closer to leading edge fin and can be divided into two groups: articulated and non-articulated (spiny). Articulated the rays are divided along their length into separate segments; they are soft and can bend. Unarticulated– hard, with a sharp apex, tough, can be smooth or jagged (Fig. 10).

Figure 10 – Fin rays:

1 – unbranched, segmented; 2 – branched; 3 – prickly smooth; 4 – prickly jagged.

The number of branched and unbranched rays in the fins, especially in unpaired ones, is an important systematic feature. The rays are calculated and their number is recorded. Non-segmented (spiny) ones are designated by Roman numerals, branched ones - by Arabic numerals. 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 for the dorsal fin of pike perch is as follows: D XIII-XV, I-III 19-23. In the anal fin of pike perch, the number of spiny rays is 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 late loss. Cyclostomes (Cyclostomata) do not have paired fins. This is a primary phenomenon.

The pectoral fins are located behind the gill slits of fish. In sharks and sturgeon, the pectoral fins are located in a horizontal plane and are inactive. These fish have a convex dorsal surface and a flattened ventral side of the body that gives them a resemblance to the profile of an airplane wing and creates lift when moving. Such an asymmetry of the body causes the appearance of a torque that tends to turn the fish’s head down. Pectoral fins and rostrum of sharks and sturgeon fish V functionally make up unified system: directed at a small (8-10°) angle to the movement, they create additional lifting force and neutralize the effect of torque (Fig. 11). If a shark's pectoral fins are removed, it will raise its head upward to keep its body horizontal. In sturgeon fish, the removal of pectoral fins is not compensated for in any way due to poor flexibility of the body in the vertical direction, which is hampered 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 connected, the 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 noticeable in the hammerhead shark (Sphyrna) and the saw shark (Pristiophorus), whose rostrum is highly developed and the pectoral fins are small, whereas in 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 during forward movement shark or sturgeon in the direction of the longitudinal axis of the body:

1 - center of gravity; 2 – center of dynamic pressure; 3 – force of residual mass; V0– lift force created by the body; Vр– lifting force created by the pectoral fins; Vr– lifting force created by the rostrum; Vv– lifting force created by the pelvic fins; Vс– lift force created by the caudal fin; Curved arrows show the effect of torque.

The pectoral fins of bony fish, unlike the fins of sharks and sturgeons, are located vertically and can perform rowing movements back and forth. The main function of the pectoral fins of bony fishes is low-speed propulsion, allowing precise maneuvering when searching for food. The pectoral fins, together with the pelvic and caudal fins, allow the fish to maintain balance when motionless. The pectoral fins of stingrays, which evenly border their body, serve as the main propellers when swimming.

The pectoral fins of fish are very diverse in both 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 pectoral fins of fish:

1 - flying fish; 2 – slider perch; 3 – keel belly; 4 – body; 5 – sea rooster; 6 - angler.

fish soar in the air. U freshwater fish keelbellies from the Characin family, enlarged pectoral fins allow the fish to fly, reminiscent of the flight of birds. U sea roosters(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. Representatives of the order Anglerfish (Lophiiformes) have pectoral fins with fleshy bases that are also adapted to move along the ground and quickly bury themselves in it. Moving along hard substrates with the help of pectoral fins made these fins very mobile. When moving along 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 during serpentine movements of the body while moving along the bottom. The pectoral fins of jumpers (Periophthalmidae) are arranged in a unique way. Their bases are equipped with special muscles that allow the fin to move forward and backward, and have a bend reminiscent of the elbow joint; The fin itself is located at an angle to the base. Living on coastal shallows, jumpers with the help of pectoral fins are able not only to move on land, but also to climb up plant stems, using the caudal fin with which they clasp the stem. With the help of pectoral fins, slider fish (Anabas) also move on land. Pushing off with their tail and clinging to plant stems with their pectoral fins and gill cover spines, these fish are able to travel from body of water to body of water, crawling hundreds of meters. In such bottom-dwelling fish as rock perches(Serranidae), sticklebacks (Gasterosteidae), and wrasse (Labridae), pectoral fins are usually wide, rounded, fan-shaped. When they work, undulation waves move vertically downward, the fish appears to be suspended in the water column and can rise upward like a helicopter. Fishes of the order Pufferfish (Tetraodontiformes), pipefish (Syngnathidae) and pipits (Hyppocampus), having small gill slits ( operculum hidden under the skin), they 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 fish's body. Their position changes with the change in the center of gravity (Fig. 13). In low-organized fish (herring-like, carp-like) the pelvic 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 due to their non-compact position internal organs occupying a large cavity. In highly organized fish, the pelvic fins are located in the front of the body. This position of the pelvic fins is called thoracic and is characteristic primarily of most perciform fish.

The pelvic fins can be located in front of the pectoral fins - 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 order Codfish, as well as large-headed fish of the order Perciformes: stargazers (Uranoscopidae), nototheniids (Nototheniidae), blennies (Blenniidae), etc. Pelvic fins are absent in fish with eel-shaped and ribbon-shaped bodies. In erroneous (Ophidioidei) fish, which have a ribbon-eel-shaped body, the pelvic fins are located on the chin and serve as organs of touch.

Figure 13 – Position of the ventral fins:

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

The pelvic fins can be modified. With their help, some fish attach to the ground (Fig. 14), forming either a suction funnel (gobies) or a suction disk (lumpfish, slugs). The ventral fins of sticklebacks, modified into spines, have a protective function, and in triggerfishes, the pelvic fins have the appearance of a spiny spine and, together with the spiny ray of the dorsal fin, are a protective organ. In male cartilaginous fish, the last rays of the ventral fins are transformed into pterygopodia - copulatory organs. In sharks and sturgeons, the pelvic fins, like the pectoral fins, perform the function bearing planes, however, their role is less than that of the pectorals, since they serve to increase lifting force.

Figure 14 - Modification of the pelvic fins:

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

Cartilaginous fish.

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

The pelvic girdle is 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 ventral fins is attached to its ends. The pelvic fins have only one basal element. It is greatly elongated and one row of radial cartilages is attached to it. The rest of the free fin is supported by elastin threads. In males, the elongated basal element continues beyond the fin blade as the skeletal basis of the copulatory outgrowth.

Unpaired fins: Typically represented by a caudal, anal, and two dorsal fins. The tail fin of sharks is heterocercal, i.e. its upper lobe is significantly longer than the lower one. The axial skeleton, the spine, enters it. The skeletal base of the caudal fin is formed by elongated upper and lower vertebral arches and a number of radial cartilages attached to the upper arches of the caudal vertebrae. Most of The tail blades are supported by elastin threads. At the base of the skeleton of the dorsal and anal fins lie radial cartilages, which are embedded in the thickness of the muscles. The free blade of the fin is supported by elastin threads.

Bony fish.

Paired fins. Represented by pectoral and ventral fins. The shoulder girdle serves as support for the pectorals. The pectoral fin at its base has one row of small bones - radials, extending from the scapula (which makes up the shoulder girdle). The skeleton of the entire free fin blade consists of segmented skin rays. The difference from cartilaginous ones is the reduction of basalia. The mobility of the fins is increased, since the muscles are attached to the expanded bases of the skin rays, which movably articulate with the radials. The pelvic girdle is represented by paired flat triangular bones closely interlocking with each other, lying in the thickness of the muscles and not connected with the axial skeleton. Most teleost pelvic fins lack basalia in the skeleton and have reduced radials - the blade is supported only by cutaneous rays, the expanded bases of which are directly attached to the pelvic girdle.

Unpaired limbs.

Paired limbs. Review of the structure of paired fins in modern fish.

They are represented by dorsal, anal (subcaudal) and caudal fins. The anal and dorsal fins consist of bony rays, divided into internal (hidden in the thickness of the muscles) pterygiophores (corresponding to radials) and external fin rays - lepidotrichia. The caudal fin is asymmetrical. In it, a continuation of the spine is the urostyle, and behind and below it, like a fan, there 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 external 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 ones it is horizontal to support it in the water, and in bony ones it is vertical, since they have a swim bladder. Fins perform various functions when moving:

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

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Pelvic fin

Page 1

The pelvic fins are fused and form a sucker. Black, Azov, Caspian and Far East. Spawning in the spring, eggs are laid in nests, the clutch is guarded by the male.

Topic 3. FISH FINS, THEIR DESIGNATIONS,

The pelvic fins have 1–17 rays, sometimes there are no fins. Scales are cycloid or absent. Veliferidae) and opahaceae (Lampri-dae); 12 births, approx. All except Veliferidae live in the pelagic zone open ocean to depth

The rudiments of the pelvic fins appear. A notch on the dorsal edge of the fin fold marks the boundary between it and the growing caudal fin. There are more melanophores, some reaching the intestinal level.

The structure of the lancelet (diagram): / - central opening surrounded by tentacles; 2 - mouth; 3 - pharynx; 4 - gill slits: 5 - genitals: 6 - liver: 7 - intestine; 8 - anus; 9 - ventral fin: 10 - caudal fin; // - dorsal fin; / 2 - eyespot; 13 - olfactory fossa; 14 - brain; 15 - spinal cord; 16 - chord.

The pectoral and usually the dorsal and anal fins are absent. Pelvic fins with 2 rays or absent. The scales are cycloid or absent. The gill openings are connected into a single slit on the throat. The gills are usually reduced, and there are devices for air in the pharynx and intestines.

The pelvic fins are long, with 2–3 rays. Fossil forms are known from the Pleistocene and Holocene.

The anal and ventral fins are crimson. The iris of the eyes, unlike roaches, is greenish. Lives in rivers and reservoirs of Eurasia; in the USSR - in Europe. Siberia (before Lena), Puberty at 4 - 6 years.

The separation of the dorsal and anal fins begins. The rudiments of the pelvic fins appear. The rays in the caudal fin reach the posterior edge.

The dorsal and anal fins are long, almost reaching the caudal fin, the paired pelvic fins are in the form of long threads. The body of males has alternating blue and red transverse stripes; throat and parts of fins with metallic. Lives in overgrown reservoirs of the South. Produces sterile hybrids with labiaza (C.

Known from the Jurassic, they were numerous in the Cretaceous. In addition to the copula, organs (pterygopodia), formed from the outer rays of the ventral fins, males have spiny frontal and abdominal appendages that serve to hold the female.

The dorsal fin is short (7 - 14 rays), located above the ventral fins. They live in the waters of the North.

Haeckel): the formation of the gonads in higher animals in the mesoderm, and not in the ecto- or endoderm, as is the case in lower multicellular organisms; The formation and location of the paired pelvic fins in some bony fishes is not behind, as usual, but in front of the pectoral fins.

Body laterally compressed or ovate, long. Pelvic fins are absent in some species. A network of seismosensory channels is developed on the head.

They are related to carpozoans and garfishes. There are usually 2 dorsal fins, the first one is made of flexible, unbranched rays, the ventral fins have 6 rays. The lateral line is poorly developed. Phallostethidae) and neostetidae (Neostethidae), ca.

The body in the anterior part is rounded, in the caudal part it is laterally compressed. The skin is covered with bony tubercles; the largest ones are arranged in longitudinal rows. The pelvic fins are modified into a round sucker. Adult fish are bluish-gray, the back is almost black; during spawning, the belly and fins of males are painted a deep red color.

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Fins and types of fish movement

Fins. Their sizes, shape, quantity, position and functions are different. The fins allow the body to maintain balance and participate in movement.

Rice. 1 Fins

The fins are divided into paired, corresponding to the limbs of higher vertebrates, and unpaired (Fig. 1).

TO doubles relate:

1) chest P ( pinna pectoralis);

2) abdominal V.

Paired fish fins

(R. ventralis).

TO unpaired:

1) dorsal D ( p. dorsalis);

2) anal A (R. analis);

3) tail C ( R. caudalis).

4) fat ar (( p.adiposa).

In salmonids, characins, killer whales, and others, there is a adipose fin(Fig. 2), devoid of fin rays ( p.adiposa).

Rice. 2 Adipose fin

Pectoral fins common among bony fish. In stingrays, the pectoral fins are enlarged and are the main organs of movement.

Pelvic fins occupy different positions in fish, which is associated with the movement of the center of gravity caused by contraction abdominal cavity and a concentration of viscera in the front of the body.

Abdominal position– pelvic fins are located in the middle of the abdomen (sharks, herring, carp) (Fig. 3).

Rice. 3 Abdominal position

Thoracic position– the pelvic fins are shifted to the front of the body (perciform) (Fig. 4).

Rice. 4 Thoracic position

Jugular position– the pelvic fins are located in front of the pectoral fins and on the throat (cod fins) (Fig. 5).

Rice. 5 Jugular position

Dorsal fins there may be one (herring-like, carp-like), two (mullet-like, perch-like) or three (cod-like). Their location is different. In pike, the dorsal fin is shifted back, in herrings and cyprinids it is located in the middle of the body, in fish with a massive front part of the body (perch, cod) one of them is located closer to the head.

Anal fin Usually there is one, cod has two, and the spiny shark does not have one.

Caudal fin has a varied structure.

Depending on the size of the upper and lower blades, they are distinguished:

1)isobathic type – in the fin the upper and lower blades are the same (tuna, mackerel);

Rice. 6 Isobath type

2)hypobate type – the lower blade is lengthened (flying fish);

Rice. 7 Hypobate type

3)epibate type – the upper blade is lengthened (sharks, sturgeon).

Rice. 8. Epibathic type

Based on their shape and location relative to the end of the spine, several types are distinguished:

1) Protocercal type - in the form of a fin border (lamrey) (Fig. 9).

Rice. 9 Protocercal type -

2) Heterocercal type – asymmetrical, when the end of the spine enters the upper, most elongated blade of the fin (sharks, sturgeon) (Fig. 10).

Rice. 10 Heterocercal type;

3) Homocercal type – externally symmetrical, with the modified body of the last vertebra extending into the upper lobe (bony) (

Rice. 11 Homocercal type

The fins are supported by fin rays. In fish, branched and unbranched rays are distinguished (Fig. 12).

Unbranched fin rays can be:

1)articulated (capable of bending);

2)inarticulate hard (spiny), which in turn are smooth and jagged.

Rice. 12 Types of fin rays

The number of rays in the fins, especially in the dorsal and anal, is a species characteristic.

The number of spiny rays is indicated by Roman numerals, and the branched rays - by Arabic numerals. For example, the dorsal fin formula for river perch is this:

DXIII-XVII, I-III 12-16.

This means that the perch has two dorsal fins, the first of which consists of 13 - 17 spiny fins, the second of 2 - 3 spiny and 12-16 branched rays.

Functions of fins

Caudal fin creates driving force, provides high maneuverability of the fish when turning, acts as a rudder.
Thoracic and abdominal (paired fins ) maintain balance and act as rudders when turning and at depth.
Dorsal and anal the fins act as a keel, preventing the body from rotating around its axis.

Fish fins can be paired or unpaired. The paired ones include the thoracic P (pinna pectoralis) and the abdominal V (pinna ventralis); to the unpaired ones - dorsal D (pinna dorsalis), anal A (pinna analis) and caudal C (pinna caudalis). The exoskeleton of the fins of bony fishes consists of rays that can be branchy And unbranched. The upper part of the branched rays is divided into separate rays and has the appearance of a brush (branched). They are soft and located closer to the caudal end of the fin. Unbranched rays lie closer to the anterior edge of the fin and can be divided into two groups: articulated and non-articulated (spiny). Articulated the rays are divided along their length into separate segments; they are soft and can bend. Unarticulated– hard, with a sharp apex, tough, can be smooth or jagged (Fig. 10).

Figure 10 – Fin rays:

1 – unbranched, segmented; 2 – branched; 3 – prickly smooth; 4 – prickly jagged.

The pectoral fins are located behind the gill slits of fish. In sharks and sturgeon, the pectoral fins are located in a horizontal plane and are inactive. These fish have a convex dorsal surface and a flattened ventral side of the body that gives them a resemblance to the profile of an airplane wing and creates lift when moving. Such an 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 lifting force and neutralize the effect of rotational moment (Fig. 11). If a shark's pectoral fins are removed, it will raise its head upward to keep its body horizontal. In sturgeon fish, the removal of pectoral fins is not compensated for in any way due to poor flexibility of the body in the vertical direction, which is hampered 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 connected, the 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 noticeable in the hammerhead shark (Sphyrna) and sawnose shark (Pristiophorus), whose rostrum is highly developed and the pectoral fins are small, while in the sea fox shark (Alopiias) and the blue shark (Prionace), the pectoral fins are well developed and the rostrum is small.

Figure 11 – Diagram of vertical forces arising during the forward movement of a shark or sturgeon in the direction of the longitudinal axis of the body:

1 - center of gravity; 2 – center of dynamic pressure; 3 – force of residual mass; V 0 – lift force created by the body; V R– lifting force created by the pectoral fins; V r– lifting force created by the rostrum; V v– lifting force created by the pelvic fins; V With– lift force created by the caudal fin; Curved arrows show the effect of torque.

The pectoral fins of fish are very diverse in both 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 pectoral fins of fish:

1 - flying fish; 2 – slider perch; 3 – keel belly; 4 – body; 5 – sea rooster; 6 - angler.

fish soar in the air. In freshwater fish, keelbellies from 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. Representatives of the order Anglerfish (Lophiiformes) have pectoral fins with fleshy bases that are also adapted to move along the ground and quickly bury themselves in it. Moving along hard substrates with the help of pectoral fins made these fins very mobile. When moving along 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 during serpentine movements of the body while moving along the bottom. The pectoral fins of jumpers (Periophthalmidae) are arranged in a unique way. Their bases are equipped with special muscles that allow the fin to move forward and backward, and have a bend reminiscent of the elbow joint; The fin itself is located at an angle to the base. Living on coastal shallows, jumpers with the help of pectoral fins are able not only to move on land, but also to climb up plant stems, using the caudal fin with which they clasp the stem. With the help of pectoral fins, slider fish (Anabas) also move on land. Pushing off with their tail and clinging to plant stems with their pectoral fins and gill cover spines, these fish are able to travel from body of water to body of water, crawling hundreds of meters. In such bottom-dwelling fish as rock perches (Serranidae), sticklebacks (Gasterosteidae), and wrasse (Labridae), the pectoral fins are usually wide, rounded, and fan-shaped. When they work, undulation waves move vertically downward, the fish appears to be suspended in the water column and can rise upward like a helicopter. Fishes of the order Pufferfish (Tetraodontiformes), pipefish (Syngnathidae) and pipits (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 fish's body. Their position changes with the change in the center of gravity (Fig. 13). In low-organized fish (herring-like, carp-like) the pelvic 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 due to the non-compact position of the internal organs occupying a large cavity. In highly organized fish, the pelvic fins are located in the front of the body. This position of the pelvic fins is called thoracic and is characteristic primarily of most perciform fish.

Figure 13 – Position of the ventral fins:

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

The pelvic fins can be modified. With their help, some fish attach to the ground (Fig. 14), forming either a suction funnel (gobies) or a suction disk (lumpfish, slugs). The ventral fins of sticklebacks, modified into spines, have a protective function, and in triggerfishes, the pelvic fins have the appearance of a spiny spine and, together with the spiny ray of the dorsal fin, are a protective organ. In male cartilaginous fish, the last rays of the ventral fins are transformed into pterygopodia - copulatory organs. In sharks and sturgeons, the pelvic fins, like the pectoral fins, serve as load-bearing planes, but their role is less than that of the pectoral fins, since they serve to increase lifting force.

Figure 14 - Modification of the pelvic fins:

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

Take a closer look at the movements of the fish in the water, and you will see which part of the body takes the main part in this (Fig. 8). The fish rushes forward, quickly moving its tail to the right and left, which ends in a wide caudal fin. The body of the fish also takes part in this movement, but it is mainly carried out by the tail section of the body.

Therefore, the tail of the fish is very muscular and massive, almost imperceptibly merging with the body (compare in this regard with land mammals like a cat or a dog), for example, in a perch the body, inside of which all the insides are contained, ends only a little further than half the total length of its body, and the rest is its tail.

In addition to the caudal fin, the fish has two more unpaired fins - on top of the dorsal (in perch, pike perch and some other fish it consists of two separate protrusions located one behind the other) and below the subcaudal, or anal, which is so called because it sits on the underside of the tail, just behind the anus.

These fins prevent the body from rotating around the longitudinal axis (Fig. 9) and, like a keel on a ship, help the fish maintain a normal position in the water; In some fish, the dorsal fin also serves as a reliable weapon of defense. It can have such a meaning if the fin rays supporting it are hard, prickly needles that prevent more large predator swallow fish (ruff, perch).

Then we see the fish have more paired fins - a pair of pectoral and a pair of abdominal ones.

The pectoral fins sit higher, almost on the sides of the body, while the pelvic fins are closer together and located on the ventral side.

The location of the fins varies among different fish. Usually the pelvic fins are located behind the pectoral fins, as we see, for example, in pike (gastrofinned fish; see Fig. 52), in other fish the pelvic fins have moved to the front of the body and are located between the two pectoral fins (pectoral finned fish, Fig. 10) , and finally, in burbot and some sea fish, for example, cod, haddock (Fig. 80, 81) and navaga, the pelvic fins sit in front of the pectoral fins, as if on the throat of the fish (throat-finned fish).

The paired fins do not have strong muscles (check this on a dried roach). Therefore, they cannot influence the speed of movement, and fish row with them only when moving very slowly in calm, standing water (carp, crucian carp, goldfish).

Their main purpose is to maintain body balance. A dead or weakened fish turns over with its belly up, since the back of the fish turns out to be heavier than its ventral side (we will see why during the autopsy). This means that a living fish has to make some effort all the time so as not to tip over on its back or fall to its side; this is achieved by the work of paired fins.

You can verify this through a simple experiment by depriving the fish of the opportunity to use its paired fins and tying them to the body with woolen threads.

In fish with tied pectoral fins, the heavier head end is pulled and lowered; fish whose pectoral or ventral fins are cut off or tied on one side lie on their sides, and a fish in which all paired fins are tied with threads turns upside down, as if dead.

(Here, however, there are exceptions: in those species of fish in which the swim bladder is located closer to the dorsal side, the belly may be heavier than the back, and the fish will not turn over.)

In addition, paired fins help the fish make turns: when wanting to turn to the right, the fish paddles with the left fin, and presses the right one to the body, and vice versa.

Let us return once again to clarify the role of the dorsal and subcaudal fins. Sometimes, not only in the students' answers, but also in the teacher's explanations, it seems as if they are the ones who give the body a normal position - back up.

In fact, as we have seen, paired fins perform this role, while the dorsal and subcaudal fins, when the fish moves, prevent its fusiform body from spinning around the longitudinal axis and thereby maintain the normal position that the paired fins gave the body (in a weakened fish swimming on its side or belly up, the same unpaired fins support the abnormal position already assumed by the body).

Task 1. Complete laboratory work.

Subject: "External structure and features of fish movement."

Goal of the work: explore the features external structure and modes of movement of fish.

1. Make sure that the workplace has everything necessary to perform laboratory work.

2. Using the instructions given in paragraph 31 of the textbook, perform laboratory work, filling out the table as you observe.

3. Sketch appearance fish. Label the body parts.

4. Write down the results of your observations and draw conclusions. Note the features of fish adaptation to aquatic environment.

Fish are well adapted to life in the aquatic environment. They have a streamlined body shape, fins, and sensory organs that allow them to navigate in the water.

Task 2. Fill out the table.

Task 3. Write down the numbers of the correct statements.

Statements:

1. All fish have a streamlined body shape.

2. The body of most fish is covered with bony scales.

3. The skin of fish has cutaneous glands that secrete mucus.

4. The head of the fish imperceptibly passes into the body, and the body into the tail.

5. The tail of a fish is that part of the body that is bordered by the caudal fin.

6. There is one dorsal fin on the dorsal side of the fish’s body.

7. Pectoral fins When moving, the fish use them as oars.

8. Fish eyes do not have eyelids.

9. Pisces see objects located at close distances.

Correct statements: 1, 2, 3, 4, 5, 6, 8, 9.

Task 4. Fill out the table.

Task 5. The body shape of fish is very diverse: bream have a high body and strongly compressed laterally; in flounder - flattened in the dorso-ventral direction; in sharks it is torpedo-shaped. Explain what causes the differences in body shapes in fish.

Because of habitat and movement.

Flounder have a flattened shape because they swim slowly along the bottom.

The shark, on the contrary, moves quickly (the tarpedoid shape ensures fast movement in open water).

The bream's body is flattened laterally because it moves in bodies of water with dense vegetation.

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