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 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. 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 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 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; Vv– 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 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. 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 benthic 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 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 males cartilaginous fish the last rays of the pelvic 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.
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 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. 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 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 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; 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. 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 benthic 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.
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, 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.
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 blade is 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 of the open ocean at 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 ventral 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 in bony fishes. 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 a movement of the center of gravity caused by contraction of the abdominal cavity and concentration of viscera in the front part 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:
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.
All fins in fish are divided into paired, which correspond to the limbs of higher vertebrates, and unpaired. Paired fins include pectoral (P - pinna pectoralis) and ventral (V - pinna ventralis). Unpaired fins include the dorsal fin (D - p. dorsalis); anal (A - r. analis) and caudal (C - r. caudalis).
A number of fish (salmonids, characins, killer whales, etc.) have an adipose fin behind the dorsal fin; it lacks fin rays (p.adiposa).
Pectoral fins are common in bony fishes, while they are absent in moray eels and some others. Lampreys and hagfish are completely devoid of pectoral and ventral fins. In stingrays, the pectoral fins are greatly enlarged and play the main role as organs of their movement. Pectoral fins have developed especially strongly in flying fish. The three rays of the pectoral fin of the gurnard serve as legs when crawling on the ground.
The pelvic fins can occupy different positions. Abdominal position - they are located approximately in the middle of the abdomen (sharks, herring-shaped, carp-shaped). In the thoracic position, they are shifted to the front of the body (perch-shaped). Jugular position, fins located in front of the pectorals and on the throat (cod).
In some fish, the pelvic fins are transformed into spines (stickleback) or suckers (leaffish). In male sharks and rays, the posterior rays of the pelvic fins have been transformed into copulatory organs in the process of evolution. They are completely absent in eels, catfish, etc.
There may be a variable number of dorsal fins. In herring and cyprinids it is one, in mullet and perch morphs there are two, in cod morphs there are three. Their location may vary. In pike it is shifted far back, in herring and carp fish - in the middle of the body, in perch and cod - closer to the head. The longest and highest dorsal fin of the sailfish. In flounder, it looks like a long ribbon running along the entire back and, at the same time as the anal one, is their main organ of movement. Mackerel, tuna and saury have small additional fins behind the dorsal and anal fins.
Individual rays of the dorsal fin sometimes extend into long threads, and monkfish the first ray of the dorsal fin is shifted to the muzzle and transformed into a kind of fishing rod, like that of the deep-sea anglerfish. The first dorsal fin of the sticky fish also moved to the head and turned into a real sucker. The dorsal fin in sedentary benthic fish species is poorly developed (catfish) or absent (stingrays, electric eel).
Tail fin:
1) isobathic – the upper and lower blades are the same (tuna, mackerel);
2) hypobate – the lower lobe is elongated (flying fish);
3) epibate – the upper lobe is elongated (sharks, sturgeons).
Types of caudal fins: forked (herring), notched (salmon), truncated (cod), rounded (burbot, gobies), semilunate (tuna, mackerel), pointed (elpout).
From the very beginning, the fins have been assigned the function of movement and maintaining balance, but sometimes they also perform other functions. The main fins are dorsal, caudal, anal, two ventral and two pectoral. They are divided into unpaired - dorsal, anal and caudal, and paired - pectoral and abdominal. Some species also have an adipose fin located between the dorsal and caudal fins. All fins are driven by muscles. In many species, the fins are often modified. Thus, in male viviparous fish, the modified anal fin has turned into a mating organ; some species have well-developed pectoral fins, which allows the fish to jump out of the water. Gourami have special tentacles, which are thread-like pelvic fins. And some species that burrow into the ground often lack fins. Guppy tail fins are also an interesting creation of nature (there are about 15 species of them and their number is growing all the time). The movement of the fish begins with the tail and caudal fin, which send the body of the fish forward with a strong blow. The dorsal and anal fins provide balance to the body. The pectoral fins move the body of the fish during slow swimming, serve as a rudder, and, together with the pelvic and caudal fins, ensure the equilibrium position of the body when it is at rest. In addition, some species of fish can rely on pectoral fins or move with their help on hard surfaces. The pelvic fins perform mainly a balancing function, but in some species they are modified into a suction disc, which allows the fish to stick to a hard surface.
1. Dorsal fin.
2. Adipose fin.
3. Caudal fin.
4. Pectoral fin.
5. Pelvic fin.
6. Anal fin.
The structure of a fish. Types of tail fins: 
Truncated
Split
Lyre-shaped
24. Structure of fish skin. The structure of the main types of fish scales, their functions.
Fish skin performs a number of important functions. Located on the border between the external and internal environments of the body, it protects the fish from external influences. At the same time, separating the fish organism from the surrounding liquid medium with dissolved in it chemicals, fish skin is an effective homeostatic mechanism.
Fish skin quickly regenerates. Through the skin, on the one hand, partial release of the final metabolic products occurs, and on the other, the absorption of certain substances from the external environment (oxygen, carbonic acid, water, sulfur, phosphorus, calcium and other elements that play a large role in life). The skin plays an important role as a receptor surface: thermo-, barochemo- and other receptors are located in it. In the thickness of the corium, the integumentary bones of the skull and pectoral fin girdles are formed.
In fish, the skin also performs a rather specific – supporting – function. Muscle fibers of skeletal muscles are attached to the inner side of the skin. Thus, it acts as a supporting element in the musculoskeletal system.
Fish skin consists of two layers: an outer layer of epithelial cells, or epidermis, and an inner layer of connective tissue cells - the skin itself, dermis, corium, cutis. Between them there is a basement membrane. The skin is underlain by a loose connective tissue layer (subcutaneous connective tissue, subcutaneous tissue). In many fish, fat is deposited in the subcutaneous tissue.
The epidermis of fish skin is represented by multilayer epithelium, consisting of 2–15 rows of cells. The cells of the upper layer of the epidermis have flat shape. The lower (germ) layer is represented by one row of cylindrical cells, which, in turn, originate from the prismatic cells of the basement membrane. The middle layer of the epidermis consists of several rows of cells, the shape of which varies from cylindrical to flat.
The outermost layer of epithelial cells becomes keratinized, but unlike terrestrial vertebrates in fish, it does not die, maintaining contact with living cells. During the life of the fish, the intensity of keratinization of the epidermis does not remain unchanged, to the greatest extent it reaches some fish before spawning: for example, in male carp and whitefish, a so-called pearl rash appears in some places of the body (especially on the head, gill covers, sides, etc.) - a mass of small white tubercles that give the skin roughness. After spawning it disappears.
The dermis (cutis) consists of three layers: a thin upper (connective tissue), a thick middle mesh layer of collagen and elastin fibers and a thin basal layer of tall prismatic cells, giving rise to the two upper layers.
In active pelagic fish the dermis is well developed. Its thickness in areas of the body that provide intense movement (for example, on the caudal peduncle of a shark) is greatly increased. The middle layer of the dermis in active swimmers can be represented by several rows of strong collagen fibers, which are also connected to each other by transverse fibers.
In slow-swimming littoral and bottom-dwelling fish, the dermis is loose or generally underdeveloped. In fast-swimming fish, there is no subcutaneous tissue in the parts of the body that provide swimming (for example, the caudal peduncle). In these places, muscle fibers are attached to the dermis. In other fish (most often slow ones), the subcutaneous tissue is well developed.
The structure of fish scales:
Placoid (it is very ancient);
Ganoid;
Cycloid;
Ctenoid (youngest).
Placoid fish scales
Placoid fish scales(photo above) is characteristic of modern and fossil cartilaginous fish - and these are sharks and rays. Each such scale has a plate and a spine sitting on it, the tip of which extends out through the epidermis. The basis of this scale is dentin. The spike itself is covered with even harder enamel. The placoid scale inside has a cavity that is filled with pulp - pulp, it has blood vessels and nerve endings.
Ganoid fish scales
Ganoid fish scales has the appearance of a rhombic plate and the scales are connected to each other, forming a dense shell on the fish. Each such scale consists of a very hard substance - the upper part is made of ganoine, and the lower part is made of bone. This type of scales has a large number of fossil fish, as well as the upper parts in the caudal fin of modern sturgeons.
Cycloid fish scales
Cycloid fish scales found in bony fish and does not have a ganoine layer.
Cycloid scales have a rounded neck with a smooth surface.
Ctenoid fish scales
Ctenoid fish scales also found in bony fish and does not have a layer of ganoine; it has spines on the back side. 
Usually the scales of these fish are arranged in a tiled manner, and each scale is covered in front and on both sides by the same scales. It turns out that the rear end of the scale comes out, but underneath it is lined with another scale and this type of cover preserves the flexibility and mobility of the fish. Annual rings on the scales of a fish allow one to determine its age.
The arrangement of scales on the body of a fish occurs in rows, and the number of rows and the number of scales in a longitudinal row does not change with changes in the age of the fish, which is an important systematic feature for different species. Let's take this example - the lateral line of a golden crucian carp has 32-36 scales, while a pike has 111-148.
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. The fish uses its pectoral fins as oars when moving.
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.
Cartilaginous fish .
Paired fins: The shoulder girdle looks like a cartilaginous semi-ring lying in the muscles of the body walls behind the branchial region. On its lateral surface there are articular processes on each side. The part of the belt lying dorsal to this process is called scapular section, more ventral – coracoid region. 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 is his cutaneous lobe– supported by numerous thin elastin threads.
Pelvic girdle It 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. IN ventral fins there is 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 blade is 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 (component of the shoulder girdle). The skeleton of the entire free fin blade consists of articulated 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. They are represented by dorsal, anal (subcaudal) and caudal fins. Anal and dorsal fins consist of bone rays, divided into internal ones (hidden in the thickness of the muscles) pterygiophores(corresponding to radials) and external fin rays - lepidotrichia. Caudal fin asymmetrical. It is a continuation of the spine - urostyle, and behind and below it there are flat triangular bones like a fan - 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 cutaneous 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, 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.
