Paired and unpaired fins of fish. Structure and functions of fins. Biology at the Lyceum Location of paired and unpaired fins on pike

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

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

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

Often, different species of fish have modified fins, for example, males viviparous fish 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 - it is a keel when the fish moves); at gourami modified thread-like ventral fins are special tentacles; highly developed pectoral fins allow some fish to jump out of the water.

The fins of fish actively participate in 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 propulsion device for the fish. The dorsal and anal fins balance the fish's body in the water.

Different species of fish have different numbers of dorsal fins.
Herring and carp-like have one dorsal, mullet-like and perch-like- two, y codlike- three.
They can also be located differently: pike- displaced far back, at herring-like, carp-like- in the middle of the ridge, at perch and cod- closer to the head. U mackerel, tuna and saury there are small additional fins behind the dorsal and anal fins.

The pectoral fins are used by the fish when swimming slowly, and together with the pelvic and caudal fins they maintain the balance of the fish’s body in the water. Many bottom-dwelling fish move along the ground using pectoral fins.
However, in some fish ( moray eels, for example) pectoral and ventral fins are absent. Some species also lack a tail: gymnots, ramfichtids, seahorses, stingrays, sunfish and other species.

Three-spined stickleback

In general, the more developed a fish's fins, the more suited it is to swimming in calm water.

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

TOPIC 1.

Fish fins Organi dikhannya, zora ta rasmu.

FISH FINS

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

Paired fins include pectoral and ventral fins. Unpaired ones consist of a dorsal (one to three), caudal and anal (one or two). Salmon, grayling and other fish have an adipose fin on their back, and mackerel, tuna, and 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 fins to move, maneuver and maintain balance. The caudal fin plays the main role in moving forward in most fish. It performs the work of the most advanced propeller with rotating blades and stabilizes the movement. The dorsal and anal fins are a kind of keels for giving the fish’s body the desired stable position.

Two sets of paired fins serve for balance, braking and steering.

The pectoral fins are usually located behind the gill openings. The shape of the pectoral fins is related to the shape of the caudal fins: 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 the high speed of movement and the blows of the caudal fin, flying fish jump out of the water and soar on their wing-like 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 segmented, fleshy base. Relying on them angler moves along the bottom in leaps and bounds, as if on legs.

The location of the pelvic fins varies from fish to fish. In lowly organized fish (sharks, herring, carp) they are located on the belly. In more highly organized fish, the ventral fins move forward, occupying a position under the pectoral fins (perch, mackerel, mullet). In cod fish, the pelvic fins are located in front of the pectoral fins.

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

The pelvic 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 tear it off the stone.

From unpaired fins The caudal one deserves special attention, the complete absence of which is very rarely observed (stalker rays). Based on the shape and location relative to the end of the spine, several types of caudal fins are distinguished: asymmetrical (heterocercal) - in sharks, sturgeons, etc.; falsely symmetrical (homocercal) - in most bony fish.

The shape of the caudal fin is closely related to the fish's lifestyle and especially its ability to swim. Good swimmers are fish with lunate, fork-shaped and notched tails. Less mobile fish have a truncated, rounded caudal fin. In sailboats it is very large (up to 1.5 m long), they use it as a sail, placing it above the surface of the water. In spiny-finned fish, the rays of the dorsal fin are strong spines, often equipped with poisonous glands.

A peculiar transformation is observed in the sticky fish. Its dorsal fin moves to its head and turns into a suction disk, with the help of which it attaches to sharks, whales, and ships. In angler fish, the dorsal fin moves to the snout and extends into a long thread that serves as a bait for prey.

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 various fish:

1 - sea Horse; 2 – sunflower; 3 – moon fish; 4 – body; 5 – pipefish; 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 no long length bodies incapable of bending the body - box bodies, 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. Highly organized orders of bony fish (perciformes, mullets) 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 has the appearance of separate spines that perform a 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 the 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 typical for many cartilaginous fish 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).

External structure of fish

Fish and fish-like creatures have a body divided into three sections: head, body and tail.

Head ends at bony fish(A) at the level of the posterior edge of the operculum, in cyclostomes (B) - at the level of the first gill opening. Torso(usually called the body) in all fish ends at the level of the anus. Tail consists of a caudal peduncle and a caudal fin.

Pisces have paired and unpaired fins. TO paired fins include pectoral and pelvic fins, unpaired- caudal, dorsal (one to three), one or two anal fins and an adipose fin located behind the dorsal (salmon, whitefish). In gobies (B), the pelvic fins have changed into peculiar suckers.

Body Shape in fish it is associated with living conditions. Fish that live in the water column (salmon) usually have a torpedo- or arrow-shaped shape. Bottom-dwelling fish (flounder) most often have a flattened or even completely flat body shape. Species living among aquatic plants, stones and snags, have a strongly laterally compressed (bream) or serpentine (eel) body, which provides them with better maneuverability.

Body fish can be naked, covered with mucus, scales or shell (pipe fish).

Scales at freshwater fish Central Russia there can be 2 types: cycloid(with a smooth back edge) and ctenoid(with spines along the posterior edge). There are various modifications of scales and protective bone formations on the body of fish, in particular sturgeon bugs.

Scales on the body of fish can be arranged in different ways (in a continuous cover or in sections, like in mirror carp), and also be different in shape and size.

Mouth position- an important sign for identifying fish. Fish are divided into species with lower, upper and final mouth positions; There are also intermediate options.

Fish of near-surface waters are characterized by an upper position of the mouth (sebike, verkhovka), which allows them to pick up prey that has fallen on the surface of the water.
For predator species and other inhabitants of the water column, the final position of the mouth is characteristic (salmon, perch),
and for the inhabitants of the benthic zone and the bottom of the reservoir - the lower one (sturgeon, bream).
In cyclostomes, the function of the mouth is performed by the oral funnel, armed with horny teeth.

Mouth and oral cavity predatory fish equipped with teeth (see below). Peaceful benth-eating fish have no teeth on their jaws, but they have pharyngeal teeth for crushing food.

Fins- formations consisting of hard and soft rays, connected by a membrane or free. Fish fins consist of spiny (hard) and branched (soft) rays. The spiny rays can take the form of powerful spines (catfish) or jagged saws (carp).

Based on the presence and nature of rays in the fins of most bony fishes, it is compiled fin formula, which is widely used in their description and definition. In this formula, the abbreviated designation of the fin is given in Latin letters: A - anal fin (from the Latin pinna analis), P - pectoral fin (pinna pectoralis), V - ventral fin (pinna ventralis) and D1, D2 - dorsal fins (pinna dorsalis). Roman numerals indicate the numbers of prickly rays, and Arabic numerals indicate the numbers of soft rays.

Gills absorb oxygen from water and release carbon dioxide, ammonia, urea and other waste products into the water. Bony fish have four gill arches on each side.

Gill rakers they are thinnest, longest and most numerous in fish that feed on plankton. In predators, the gill rakers are sparse and sharp. The number of rakers is counted on the first arch, located immediately under the gill cover.

Pharyngeal teeth located on the pharyngeal bones, behind the fourth branchial arch.

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.

At the fish with tied pectoral fins the heavier head end pulls and falls down; 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).