The pectoral and ventral fins of the fish are paired. Fins and types of movement of 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. AT pelvic fins there is only one base element. It is greatly elongated and one row of radial cartilages is attached to it. The rest of the free fin is supported by elastic threads. In males, the elongated basal element extends beyond the fin lobe as the skeletal base of the copulatory outgrowth.

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

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 merges with the body (compare in this respect with terrestrial mammals like a cat or dog), for example, in a perch, the body, inside which all the insides are enclosed, ends only a little further than half the total length of its body, and everything else is already his tail.

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

These fins prevent the rotation of the body around the longitudinal axis (Fig. 9) and, like the 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 defense tool. It can have such a value if the fin rays supporting it are hard prickly needles that prevent more large predator swallow fish (ruff, perch).

Then we see more paired fins in the fish - 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 to each other and are located on the ventral side.

The location of the fins in different fish is not the same. Usually, the pelvic fins are behind the pectorals, as we see it, for example, in pike (gastro-finned fish; see Fig. 52), in other fish, the ventral fins have moved to the front of the body and are located between the two pectorals (breast-finned fish, Fig. 10) , and, finally, burbot and some marine fish, for example, cod, haddock (Fig. 80, 81) and navaga, the ventral fins sit in front of the pectoral, as if on the throat of a fish (throat-finned fish).

Paired fins do not have strong musculature (check this on dried wobble). Therefore, they cannot affect the speed of movement, and the fish row them only when moving very slowly in calm stagnant water (carp, crucian carp, goldfish).

Their main purpose is to maintain the balance of the body. A dead or weakened fish topples with its belly up, since the back of the fish is heavier than its ventral side (why - we will see at 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 on its side; this is achieved by the work of paired fins.

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

In 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 side, and a fish whose paired fins are tied with threads, as if dead, topples upside down.

(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 roll over.)

In addition, paired fins help the fish make turns: wanting to turn to the right, the fish grabs the left fin, and presses the right fin against the body, and vice versa.

Let us return once again to clarify the role of the dorsal and caudal fins. Sometimes, not only in the answers of the students, but also in the explanations of the teacher, the matter appears as if it is they who give the body a normal position - with the back up.

In fact, as we have seen, this role is played by paired fins, while the dorsal and caudal fins, when moving the fish, prevent its spindle-shaped body from spinning around the longitudinal axis and thereby maintain the normal position that the paired fins gave to the body (in a weakened fish swimming on its side or belly up, the same unpaired fins support the abnormal position already taken by the body).

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

Figure 10 - The rays of the fins:

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

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

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

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

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

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

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

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

Figure 12 - Shapes of the pectoral fins of fish:

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

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

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

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

Figure 13 - The position of the pelvic fins:

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

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

Figure 14 - Modification of the ventral fins:

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

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

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

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

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

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

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

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

Three-spined stickleback

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

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

• Read: Variety of fish: shape, size, color

Fish fins: shape, structure.

• Read more: Fish buoyancy; Swimming fish; flying fish

In different fish, the size, shape, number, position and function of the fins are different. But their original and main role is that the fins allow you to maintain the balance of the body in the water, participate in maneuvering movement.

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

A number of fish groups, in particular salmonids, characins, killer whales, and others, have a so-called adipose fin behind the dorsal fin, which is devoid of fin rays (p. adiposa).

Pectoral fins are common in bony fish, while in moray eels and some others, they are absent. Lampreys and hagfish are completely devoid of both pectoral and ventral fins. In stingrays, on the contrary, the pectoral fins are greatly enlarged and play the main role as organs of their movement. But the pectoral fins have developed especially strongly in flying fish, which allows them to jump out on high speed from the water, literally soar in the air, while flying long distances over the water. The three rays of the pectoral fin of the gurnard are completely isolated and act as legs when crawling on the ground.

The pelvic fins of various fish can take different position, which is associated with a shift in the center of gravity caused by the contraction of the abdominal cavity and the concentration of the viscera in the front of the body. Abdominal position - when the pelvic fins are located approximately in the middle of the abdomen, which we observe in sharks, herrings, cyprinids. In the thoracic position, the ventral fins are shifted to the front of the body, as in perciformes. And finally, the jugular position, in which the ventral fins are located in front of the pectoral and on the throat, like in codfish.

In some species of fish, the ventral fins are turned into spines - like a stickleback, or into a sucker, like a lumpfish. In male sharks and rays, the posterior rays of the ventral fins have evolved into copulatory organs and are called pterygopodia. The pelvic fins are completely absent in eels, catfish, etc.

At different groups fish can have a different number of dorsal fins. So, in herring-like and cyprinids, it is one, mullet-like and perch-like have two dorsal fins, and in cod-like ones there are three. In this case, the location of the dorsal fins can be different. In pike, the dorsal fin is shifted far back, in herring-like, cyprinids it is located in the middle of the body, and in fish such as perch and cod, which have a massive front part of the body, one of them is located closer to the head. The longest and highest dorsal fin of a sailboat fish, reaching really large sizes. In flounder, it has the form of a long ribbon running along the entire back and, simultaneously with almost the same anal, is their main organ of movement. And such mackerels as mackerel, tuna and saury acquired in the process of evolution small additional fins located behind the dorsal and anal fins.

Separate rays of the dorsal fin sometimes extend into long filaments, and in monkfish the first ray of the dorsal fin is shifted to the muzzle and transformed into a kind of fishing rod. It is he who acts as a bait, like a deep-sea anglerfish. The latter has a special bait on this rod, which is their luminous organ. The first dorsal fin of the sticky fish also shifted to the head and turned into a real sucker. The dorsal fin in sedentary demersal fish species is poorly developed, such as in catfish, or may be completely absent, as in stingrays. The famous electric eel also lacks a dorsal fin....