Paired fins of fish pectoral and dorsal. Fish fins: shape, structure. Gill apparatus in fish

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 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.

; 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.

Pectoral fins they are used by fish when swimming slowly, and also, together with the ventral and caudal fins, maintain the balance of the body of the fish 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.

The unpaired fins include the dorsal, anal and caudal.

The dorsal and anal fins perform the function of stabilizers, resisting the 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).

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

1 - sea Horse; 2 - sunflower; 3 - moon fish; 4 - bodywork; 5 – pipefish; 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 mode of movement is usually characteristic of fish with no great length bodies unable to bend the body - boxfish, moonfish. Only due to undulation of the dorsal fin move Sea Horses and sea needles. Such fish as flounder and sunfish, along with undulating movements of the dorsal and anal fins, swim by bending the body laterally.

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 in a functional sense a single fin fringing the body, 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, there is no dorsal fin electric eel, whose locomotor undulating apparatus 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.

Figure 17 - Modified first dorsal fin in a sticky 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).

Figure 18 - Shapes of the tail 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 most ancient type 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 fish and cartilaginous ganoids.

Homocercal, or falsely symmetrical. Outwardly, this fin can be classified as equal-lobed, 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 - hypobate, 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).

Figure 19 - Scheme of the location of the blades of the caudal fin relative to the zone of vortices and the friction layer at different form bodies:

A- with a symmetrical profile (isocercia); b- with a more convex profile contour (epicercium); V- 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 (pinna adiposa), 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.

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 mackerels, mackerels, 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).

Habitat and external structure of fish

The habitat of fish is various water bodies of our planet: oceans, seas, rivers, lakes, ponds. It is very extensive: the area occupied by the oceans exceeds 70% of the Earth's surface, and the deepest depressions go 11 thousand meters deep into the oceans.

The variety of living conditions in the water influenced the appearance of fish and contributed to a wide variety of body shapes: the emergence of many adaptations to living conditions, both in structure and in biological features.

Overall plan external structure fish

On the head of the fish are eyes, nostrils, mouth with lips, gill covers. The head smoothly merges into the body. The trunk continues from the gill covers to the anal fin. The body of the fish ends with a tail.

Outside, the body is covered with skin. Protects the skin of most slimy fish scales .

The locomotion organs of fish are fins . The fins are outgrowths of the skin that rest on the bones. fin rays . The tail fin is the most important. From the bottom on the sides of the body are paired fins: pectoral and ventral. They correspond to the fore and hind limbs of terrestrial vertebrates. The position of the paired fins varies from fish to fish. The dorsal fin is located on top of the body of the fish, and the anal fin is located below, closer to the tail. The number of dorsal and anal fins may vary.

On the sides of the body of most fish is a kind of organ that perceives the flow of water. This lateral line . Thanks to the lateral line, even a blinded fish does not run into obstacles and is able to catch moving prey. The visible part of the lateral line is formed by scales with holes. Through them, water penetrates into a channel stretching along the body, to which the endings of nerve cells fit. The lateral line may be intermittent, continuous or completely absent.

Fin functions

Thanks to the fins, the fish is able to move and maintain balance in aquatic environment. Deprived of fins, it turns over with its belly up, since the center of gravity is placed in the dorsal part.

unpaired fins (dorsal and anal) provide body stability. The caudal fin in the vast majority of fish performs the function of a mover.

Paired fins (thoracic and abdominal) serve as stabilizers, i.e. provide an equilibrium position of the body when it is immobile. With their help, the fish maintains the body in the desired position. When moving, they serve as bearing planes, a steering wheel. The pectoral fins move the fish's body when swimming slowly. The pelvic fins perform mainly the function of balance.

Fish have a streamlined body shape. It reflects the characteristics of the environment and lifestyle. In fish adapted to fast long swimming in the water column ( tuna(2), mackerel, herring, cod, salmon ), "torpedo-shaped" body shape. In predators practicing fast throws at a short distance ( pike, taimen, barracuda, garfish (1) , saury), it is "arrow-shaped". Some fish adapted to long stay at the bottom ( slope (6) , flounder (3) ) have a flat body. In some species, the body has a bizarre shape. For example, sea ​​Horse resembles the corresponding chess piece: its head is at right angles to the axis of the body.

Sea Horses inhabit different oceans globe. These fish surprise anyone who observes them: the body, like an insect, is enclosed in a shell, the prehensile tail of a monkey, the rotating eyes of a chameleon and, finally, a bag, like a kangaroo.

Although this pretty fish can swim upright with the help of the oscillating movement of its dorsal fin, it is a poor swimmer and spends most of its time hanging, clinging to seaweed with its tail and looking out for small prey. The tubular snout of the skate acts like a pipette - when the cheeks swell sharply, the prey is quickly drawn into the mouth from a distance of up to 4 cm.

Considered the smallest fish Filipino goby Pandaku . Its length is about 7 mm. At one time, fashionistas wore these fish in ... ears. In crystal earrings-aquariums!

most big fish consider whale shark which reaches a length of 15 m.

Additional fish organs

Some species of fish (for example, carp or catfish) have antennae around the mouth. These are additional organs of touch and determination of the taste of food. Many marine deep-sea fish (for example, deep sea anglerfish, hatchet fish, anchovy, photoblepharon ) developed luminous organs.

Protective spikes are found on the scales of fish. They may be located in different parts body. For example, thorns cover the body hedgehog fish .

Some fish, for example scorpionfish, sea ​​Dragon, warty have organs of defense and attack - poisonous glands located at the base of the spikes and fin rays.

body integuments

Outside, the skin of fish is covered with scales - thin translucent plates. Scales with their ends overlap each other, arranged in a tile-like manner. This provides

strong protection of the body and at the same time does not create obstacles to movement. Scales are formed by special skin cells. The size of the scales is different: from microscopic to acne up to several centimeters Indian barbel . There is a wide variety of scales: in shape, strength, composition, quantity and some other characteristics.

Lie in the skin pigment cells - chromatophores : when they expand, the pigment grains spread over a larger area and the color of the body becomes bright. If the chromatophores contract, pigment grains accumulate in the center, leaving most of the cell uncolored, and the color of the body turns pale. If the pigment grains of all colors are evenly distributed inside the chromatophores, the fish has bright color; if the pigment grains are collected in the centers of the cells, the fish becomes almost colorless, transparent; if only yellow pigment grains are distributed over their chromatophores, the fish changes color to light yellow.

Chromatophores determine the diversity of fish coloration, especially bright in the tropics. Thus, the skin of fish performs the function of external protection. It protects the body from mechanical damage, facilitates sliding, determines the color of the fish, communicates with external environment. The skin contains organs that sense temperature and chemical composition water.

Coloring value

Pelagic fish often have a dark "back" and a light "belly", like this fish. abadejo cod family.

Indian glass catfish can serve as a guide to the study of anatomy.

Many fish that live in the upper and middle layers of the water have a darker color in the upper part of the body and a light color in the lower. The silvery belly of the fish, when viewed from below, will not stand out against the light background of the sky. Similarly, a dark back, when viewed from above, will blend into the dark background of the bottom.

By studying the coloration of fish, you can see how camouflage and imitation of other types of organisms occur with its help, observe a demonstration of danger and inedibility, as well as the presentation of other signals by fish.

In certain periods of life, many fish acquire a bright breeding color. Often the color and shape of the fish complement each other.

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The hydrosphere is characterized by an extraordinary variety of conditions. These are fresh, running and stagnant waters, as well as salty seas and oceans inhabited by organisms at different depths. To exist in such a variety of conditions, fish have developed both general principles structures that meet the requirements of the environment (smooth, without protrusions, an elongated body covered with mucus and scales; a pointed head with pressed gill covers; a system of fins; a lateral line), as well as adaptations characteristic of individual groups (flattened body, light organs, etc.). Each species of fish has numerous and varied adaptations corresponding to a certain way of life.

THEME 1.

Fish fins. Organi dihannya, zoru that hearing.

FISH FIN

The fins are characteristic feature fish structures. They are divided into paired, corresponding to the limbs of higher vertebrates, and unpaired, or vertical.

Paired fins include pectoral and pelvic fins. Unpaired ones consist of dorsal (from one to three), caudal and anal (one or two). Salmon, grayling and other fish have an adipose fin on their back, while mackerel, tuna, saury have small additional fins behind the dorsal and anal fins. The position of the fins on the body, their shape, size, structure and functions are very diverse. Fish use their fins to move, maneuver and maintain their balance. In moving forward, the main role in most fish is played by the caudal fin. It does the work of the most advanced propeller with rotary blades and stabilizes the movement. The dorsal and anal fins are a kind of keels to give the body of the fish the desired stable position.

Two sets of paired fins are used for balance, braking and control.

The pectoral fins are usually located behind the gill openings. The shape of the pectoral fins is related to the shape of the caudal: they are rounded in fish that have a rounded tail. Good swimmers have pointed pectoral fins. The pectoral fins of flying fish are especially strongly developed. Thanks to high speed movements and strokes of the caudal fin, flying fish jump out of the water and soar on pterygoid pectoral fins, covering a distance of up to 100-150 m in the air. Such flights help them hide from the pursuit of predators.

The pectoral fins of the monkfish have a jointed, fleshy base. Relying on them angler moves along the bottom in leaps, as if on legs.

The location of the ventral fins in different fish is not the same. In low organized (sharks, herring, cyprinids) they are on the belly. In more highly organized, the pelvic fins move forward, taking a position under the pectorals (perch, mackerel, mullet). In codfish, the pelvic fins are in front of the pectoral fins.

In gobies, the pelvic fins are fused into a funnel-shaped sucker.

The ventral fins of the lumpfish have changed into an even more amazing adaptation. Their suction cup holds the fish so firmly that it is difficult to remove it from the stone.

Of the unpaired fins, the caudal fin deserves special attention, the complete absence of which is very rare (stingrays). According to the shape and location relative to the end of the spine, several types of caudal fins are distinguished: asymmetric (heterocercal) - in sharks, sturgeons, etc .; falsely symmetrical (homocercal) - in most bony fish.

The shape of the caudal fin is closely related to the way of life of the fish6 and especially to the ability to swim. Good swimmers are fish with crescent, forked and notched tails. Less mobile fish have a truncated rounded tail fin. For sailboats, it is very large (up to 1.5 m long), they use it as a sail, exposing it above the surface of the water. In spiny fish, the rays of the dorsal fin are strong spines, often equipped with poisonous glands.

A peculiar transformation is observed in the sticky fish. Her dorsal fin moves to her head and turns into a suction disk, with which she attaches herself to sharks, whales, and ships. In anglers, the dorsal fin is shifted to the muzzle and stretched into a long thread that serves as a bait for prey.