About animals

Fish class

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Representatives of bone fish have a bone or bone-cartilaginous skeleton. According to the old systematics, bone fish were distinguished in the rank of a class in which there were four subclasses: cartilaginous (sturgeon), ray-finned (overwhelming majority of fish), double-breathing (protopterus), and brush-tailed (latimeria). According to the new systematics, bone fish is a group that includes two classes: ray-finned and lapellate-fish.

Bone fish appeared around Devonian. Today there are about 30 thousand species.

Fish in the process of evolution acquired a lot of progressive structural features that allowed them to adapt to the diverse conditions of aquatic life, and therefore, fish are diverse in terms of life and body shape.

Bone fish skin

The outer cover of fish forms the epidermis (multilayer epithelium) and the dermis (connective tissue). In the epidermis there are glands that secrete mucus, which reduces the friction of the body against water when the fish move.

Bone scales. This distinguishes bone fish from cartilaginous, in which the scales are placoid (has a different origin and structure).

In the skin of the fish there are pigment cells that determine the color of the body. Some species of fish can change their color, adapting to the surrounding background.

Fish aromorphoses

Fishes differ from previous evolutionary forms in new, progressive structural features that have increased their level of organization. Let's list them.

    The appearance of the jaws and skull

In fish, the first pair of gill arches is modified in the jaw, with the help of which nutrition - capture, grinding of prey becomes possible. A skull appeared - a bone reservoir of the brain and sensory organs, which reliably protects these structures of the nervous system.

The precursors of the extremities, fins, paired appendages of the body, isolated from the trunk and head, are set in motion by muscular strength.

In cartilage fish, the chord has a cartilaginous structure throughout life, and in bone fish, the chord is ossified: the cartilage tissue turns into bone tissue. The chord (axial skeleton) is also called - the spine.

Swimming bubble

This organ is characteristic exclusively of bone fish: it is absent in cartilaginous fish (sharks, stingrays). A swimming bladder is an air bag filled with a mixture of gases: nitrogen, oxygen, carbon dioxide.

It performs a number of critical functions:

  • Hydrostatic - helps to occupy a certain position in the water column. So when the bubble expands, the fish floats, and when it decreases, it sinks to the bottom.
  • Respiratory - able to perform lung function
  • Baroreceptor - perceives pressure changes
  • Acoustic - perceives sounds, plays a role similar to the ear

When filled with gas, the bubble expands: this changes the specific gravity of the fish, it decreases and the fish floats. The reverse pattern occurs when the bubble decreases. But where does the gas that fill the bubble come from if the fish lives in the water? Answering this question, we note that all fish are divided into two types: open-bubble and closed-bubble.

In open-bubble fish, the swim bladder communicates with the digestive system. Throughout their life, they rise to the surface of the water and swallow air, as needed, they can be released from the gases, squeezing them through the throat, and then the mouth into the environment. Such fish include herring-like, pike-like, carp-like, lonely.

Closed-bubble fish have a bladder that does not communicate with the digestive tube. Gases enter it due to gas secretion: they pass from a dissolved (in the blood) state to a gaseous state, filling the bubble. When the bubble decreases, the gases dissolve in the blood again, returning to the bloodstream. Such fish include: cod-shaped, perch-shaped, mullet-shaped.

© Bellevich Yuri Sergeevich

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Subclass Cartilage (Chondrosten)

A small ancient group of primitive in some respects fish, which have a number of features common to cartilage fish. In appearance, they are somewhat similar to sharks. There is a rostrum, in connection with which the oral opening is located on the underside of the head in the form of a crescent transverse fissure. The caudal fin, like sharks, is unequal-shaped, heterocercal. Paired fins are located horizontally. The scales are peculiar, in the form of large bone plates, the so-called bugs.

The basis of the axial skeleton is a lifelong chord, dressed in a thick connective tissue case. The vertebral bodies do not develop, but there are cartilaginous upper and lower arches of the vertebrae. The brain skull is almost entirely cartilaginous, covered on the outside with the skin bones that form the roof, sides (nasal, frontal, parietal bones) and the bottom of the skull (parasphenoid and vomer). There is a bone gill cover. In the intestine, a spiral valve is well defined. There is a swim bladder communicating with the intestines. The arterial cone is preserved in the heart. There are no copulative organs, external fertilization, small caviar.

You can see that the cartilaginous fish retain a number of features of the cartilaginous fish: rostrum, transversal, heterocercal caudal fin, horizontal paired fins, spiral intestinal valve, arterial cone of the heart. On the other hand, they have features common to all other bone fish: the bony parts of the skeleton, the gill cover, the reduced (although partially) inter-gill septum, the swim bladder, the small and unshell eggs, and the external insemination.

Fish skeleton

The skeleton of fish makes up the spine, brain skull, visceral skeleton, skeleton of paired limbs and their belts.

Just as in cartilaginous bone fish, the spine is divided into the trunk and tail sections.

Ribs extend from the transverse processes of the vertebral bodies. The ribs end freely, they serve as a defense to internal organs.

The rays of paired fins are bone, connected to the bones of the limb belts. The fin moves relative to its belt as a single lever. Belts of limbs of bone fish lie in soft tissues freely.

The muscular system retains a metameric structure, but is more complex than that of cartilaginous fish. Muscles are attached to the bones of the skeleton.

Fish swim due to the movement of the caudal fin. Paired limbs - pectoral and ventral fins - perform the function of rudders of depth.

Nervous system and sensory organs of fish

The spinal cord of fish is located in the canal formed by the superior arches of the vertebrae. Thus, the spinal cord is well protected.

The brain is protected by the cranium and consists of five sections: the forebrain with olfactory lobes, the intermediate and midbrain, the cerebellum, the medulla oblongata. The cerebellum and midbrain are most developed in bone fish. The first is responsible for the coordination of movements, and in the second there are visual centers.

In the eyes there is a spherical lens, the cornea is thickened. Accommodation is achieved due to the movement of the lens, and not a change in its shape (as, say, in mammals). Fishes are usually seen in the distance up to 15 m, i.e. their lens is adapted for vision at close range. This adaptation of vision during evolution is due to the low transparency of water. Eyes have eyelids.

Nostrils lead into closed olfactory sacs. The olfactory receptors are located there.

Well developed organs of chemical sensation (smell and taste). Taste buds in bone fish are found not only in the oral cavity, but also in various places on the skin of the body.

The organ of hearing and balance consists of the inner ear, which includes three semicircular canals (the organ of equilibrium), and a hollow sac that perceives sound vibrations. Due to the density of water, sound waves are transmitted through the bones of the skull and reach the hearing organs (in other words, there is no need for an external opening). Fish can make sounds (creak, clicks). Such sounds act as signals when searching for food and during reproduction. Sounds are made using the friction of teeth, bones, with a change in the volume of the swimming bladder.

Tactile tactile cells are located throughout the body.

Sideline organ

Fish have a unique sideline organ. It consists of sensitive cells that are located at the bottom of the grooves or in the channels on the body of the fish. These channels or grooves have openings in the external environment. Sensitive cells of the lateral line organ have cilia. Channels stretch on both sides of the whole body of the fish.

The function of the lateral line organ is the perception of water vibrations. Using the sideline of the fish, the speed and direction of the current, the presence of objects nearby and even fluctuations in the intensity of magnetic and electric fields are determined.

Systematics and ecology of cartilage

Modern cartilage fish are represented by only one order of sturgeon (Acipenseriformes). A few species of this order are distributed in the northern hemisphere and mainly in its temperate latitudes. There are two families.

Sturgeon family (Acipenseridae). Their rostrum is often pointed, their mouth is small, and adults have no teeth. The majority of modern species belong to this family. We will mention several types of sturgeons among them: the Russian sturgeon (Acipenser guldenstadti), distributed in the basins of the Black and Caspian Seas, the Siberian sturgeon (A. baeri), found in our northern rivers from the Pechora in the west to Kolyma in the east and in the pre-estuary spaces of the Arctic Ocean , Amur sturgeon (A. schrenki) inhabiting the Amur. Stellate sturgeon (A. stellatus) is found in the Azov, Black and Caspian seas. Sterlet (A. ruthenus), which lives in many rivers of the basins of the Caspian, Black Seas and the Arctic Ocean (to the east, to the Yenisei, inclusive), is close to sturgeons. A special kind of sturgeon is made up of two species of beluga. European Beluga (Huso huso) lives in the basins of the Caspian, Black and Adriatic Seas, the Far Eastern Beluga (N. dauricus), often called Kaluga, lives in the Amur basin. These are the largest freshwater fish, reaching a weight of more than 1000 kg and an age of more than 100 years. In the Syr Darya and Amu Darya, peculiar pseudopatonids (Pseudoscaphirnynchus) live, characterized by a wide and flattened snout. The sizes are small, weight up to 1 kg.

There are sturgeon species (less numerous) in North America.

The family of paddlefish (Polyodontidae) is characterized by the fact that in its species the snout is elongated into a long paddle-shaped lobe, their mouth is large and the jaws carry small teeth. The skin is bare. Distributed in North America and Southeast Asia, in the Mississippi, Yellow River and Yangjiang basins.

Cartilaginous partly freshwater, partly migratory fish. Sterlet and the American lake sturgeon spend their whole lives in fresh waters and do not make large migrations. Beluga, Russian sturgeon, stellate stellate fatten in the coastal waters of the seas, and go into spawning rivers to spawn, which often rise far up.

Spawning occurs in the spring, but most migratory species have two entries into the rivers: in spring, when fish with mature sexual products go and spawning in the same spring, and in autumn, when the incoming fish winter in the rivers and spawn the next spring. Spawning occurs in the bottom layers of water. Caviar remains at the bottom or buried in the ground (American sturgeon). The hatched fry slide down into the mouth areas where they are fed until puberty. The latter comes late: at the sterlet - at the age of 4-6 years, at the Russian sturgeon - at the age of 8-15 years, at the beluga - at 15-18 years. Fertility compared with most other bone fish is small. Thus, sterlet sweeps 4-140 thousand eggs, Siberian sturgeon - 50-500 thousand, Russian sturgeon - 70-840 thousand, and the most prolific Kaluga - 500-4500 thousand eggs.

They eat animal food. Beluga is a predator eating fish, and sometimes young seals. Sturgeons eat a lot of shellfish. Sterlet feeds mainly on insects.

Sturgeons are of great commercial importance. The stocks of these fish in Western Europe and North America are greatly depleted. In our country, sturgeon fishing in the basins of the Caspian and Black Seas is of the greatest importance.

Digestive system of fish

There are undifferentiated teeth in the oral cavity of bone fish. The teeth can be located not only on the jaw, but also on the palatine and some other bones. The teeth of fish perform only the functions of capturing and holding prey, but do not grind food. Fish just swallow food. They do not have salivary glands.

Behind the oral cavity is the pharynx and esophagus, which opens into the stomach. Gastric juice contains hydrochloric acid and pepsin, which partially break down food. Further digestion occurs in the intestines with the help of the secrets of the liver and pancreas. In herbivorous species of bone fish in the intestines live symbiotic protozoa and bacteria that secrete enzymes that help digest food.

Fish fry feed on plankton. The food of adult bone fish is diverse, many are omnivores.

Subclass Radius (Actinopterygii)

The most numerous (over 90% of living species) and widespread subclass of modern fish. Its species are found in all seas and oceans in which they inhabit various horizons. Many species live in fresh water bodies: rivers, lakes, ponds.

Due to the variety of living conditions and lifestyle, the appearance of these fish is extremely diverse. However, ray-feathers are characterized by a number of common features of the organization. So, their skeleton is almost entirely bone and cartilage is preserved only in small areas between the bones that displace it. The skeleton of paired fins is simplified, as a rule, there are no basal fins in the pectoral fins, and bone radials are attached directly to the belt. In the ventral fins there are not only basal, but also radials, and the skeleton of the fins consists of only bone rays.

Paired fins are located vertically relative to the body. The rostrum is usually not, and the mouth is located on the front end of the head. No cesspool. Caudal fin homocercal. The body is covered with bone scales, which are thin bony plates overlapping one another on a tile-like basis (in only one case, the scales are not bone, but ganoid in the shell pike).

The peculiarities of the organization of ray-fin fish will be considered on the example of bony fish, representing their most numerous and typical group (superorder Teleostei).

Skin integument

The body is covered with bone scales, representing thin translucent plates with a smooth (cycloid scales) or jagged (ctenoid scales) outer edge. Scales are formed only due to the skin itself (corium). Outside, the scaly cover is covered with a thin layer of the epidermis. In the latter there are many unicellular glands secreting their secret - mucus - to the surface of the body.

The size of the scales increases with the growth of the body of the fish (which runs almost throughout the life of an individual). The rate of increase in the size of the scales is not the same in different periods of the year.

A lateral line is located in the skin, which represents a paired canal that runs along the sides of the body and communicates with the external environment through a series of holes perforating the scales.

The spine is represented by bony amphicel vertebrae. The spinal column is divided only into the trunk and tail sections. Vertebrae bear the upper and lower arches. In the trunk, only the superior arches are closed, forming the spinal canal, the arches here carry spinous processes. The lower arches of the trunk section do not close, do not have spinous processes and ribs are attached to them. The latter, unlike cartilaginous fish, delimit the body cavity not only from above, but also from the sides. In the caudal region, the spinous processes are not only on the upper, but also on the lower arches.Closure of the latter leads to the formation of a hemal canal.

The skull is mostly bony, formed by both false and chondral bones.

Brain skull

Chondral ossification. Four occipital bones develop in the occipital region. Down from the occipital foramen lies the main occipital bone (basioccipitale), on the sides of this foramen there is a paired lateral occipital bone (exoccipitale), and, finally, the occipital foramen is bounded from above by the superior occipital bone (supraoccipitale).

In the area of ​​the auditory capsule, the ear bones (otici) develop. Their number is usually five (on each side of the skull).

Sphenoid bones are formed in the area of ​​the orbit (which does not completely ossify completely): the unpaired main sphenoid bone (basisphenoideum), which forms the lower-posterior angle of the orbit, and paired winged-winged (alisphenoideum) and ocular-shaped bones (orbitosphenoideum). They make up the anteroposterior and middle parts of the orbit.

In the area of ​​olfactory capsules, an unpaired median olfactory bone (mesethmoideum) and paired lateral olfactory bone (ectoethmoideum) develop.

Thus, chondral ossifications form the back of the brain skull, its sides and partly the bottom, but not the roof, in which the fountain remains.

The false bones of the brain skull form its roof and partly its sides and bottom. In the front of the roof are paired nasal bones, then paired frontal bones (frontale) lie, and finally, even further to the occipital region, paired parietal bones (parietale) are located. The bottom of the skull is composed mainly of parasphenoid (parasphenoideum) and an unpaired opener (vomer) lying in front of it. Around the orbit there are a number of small bones that form the periorbital ring.

Bone fish respiratory system

Bony fish have from 5 to 7 pairs of gill slots supported by gill arches and covered on each side by one gill cover.

During embryonic development, gill openings form in the anterior portion of the digestive tube.

Gill lobes are located on the branchial arches, in which there is a dense network of small capillaries. This is where gas exchange takes place.

The movement of water and the washing of the gill lobes is provided by the movements of the mouth and gill covers. Bone fish suck water through the mouth and expel it through gill slots. At the same time, water washes the gill petals.

In addition to gills breathing, a number of fish partially carry out gas exchange with the help of the skin. They can also swallow air, in which case oxygen is absorbed by the intestines.

Fish circulatory system

The heart of the fish is two-chamber (one atrium and one ventricle), therefore, there is only one circle of blood circulation. Venous blood passes through the heart, which is then sent to the gills. From there, arterial blood through the efferent gill arteries enters the spinal aorta and spreads through the vessels departing from it through the tissues. Having given oxygen, blood collects through the veins in the atrium.

Thus, the gill arteries delivering venous blood from the heart, and the gill arteries that carry arterial blood are combined into the spinal aorta.

The heart in fish is rare and weak. So at the perch there are 20 cuts per minute. Therefore, fish have a fairly slow metabolism. Fish are cold-blooded (their body temperature depends on the ambient temperature).

Visceral skull

The visceral skull, due to the ossification of the skeleton, undergoes a greater change than its brain part.

The upper part of the jaw arch, homologous to the non-square cartilage, is replaced in its anterior part by a palatine bone mixed in origin, in the middle part by three pterygoids (pterygoideum), of which two are cutaneous and one chondral in origin, and in the back part by a chondral square bone (quadratum). The system of these bones in the fish being analyzed completely loses the function of the upper jaw and to a greater extent forms the bottom of the skull. The role of the upper jaw is performed by paired, skin-derived bones: maxillary (maxillare) and premaxillary (praemaxillare).

The lower jaw is represented by a large, skin-borne tooth bone (dentale), covering the Meckel cartilage of skin origin, the angular bone (angulare), which forms the lower-posterior angle of the jaw, and the only chondral bone - articular (articulare), which articulates with a square bone.

The sublingual arch is represented basically by the same elements as in cartilaginous fish, i.e., paired hyomandibular, hyoid and unpaired copula. All these parts are bone, of chondral origin. To the posterior edge of the lower part of the hyoid arch, a number of long bones are attached - rays of the gill membrane.

Gill arches of the same structure as those of cartilaginous fish, but bony, in addition, the last (fifth) arch is greatly reduced. A new acquisition of bone fish is the gill cover (operculum), represented by four flat false bones.

Excretory system

The excretory system of fish is represented by two trunk kidneys, which have a ribbon-like shape.

In most bone fish, ammonia is the final protein breakdown material. It is toxic and requires a lot of water to remove it from the body.

Urine from the kidneys through the ureters enters the bladder, from where it leaves through an independent opening. Partially, the decay products of fish are removed through the gills in the process of respiration.

Bone fish breeding

The vast majority of fish are dioecious. However, as an exception, there are hermaphroditic species in which the sex glands alternately perform the functions of either the testes or ovaries. But in sea bass, different parts of the gonads simultaneously form spermatozoa and eggs.

Reproduction is only sexual. In bone fish, fertilization is almost always external.

The fish is characterized by great fecundity, since with external fertilization a lot of eggs are not fertilized. In addition, many fry die. In fish caring for offspring, fertility is lower.

Some species (salmon, etc.) breed once in a lifetime, after which they die.

Individual development occurs with incomplete transformation. Larvae of fish are called fry.

Limbs and their belts

The skeleton of the pectoral fins does not have basal and consists of bone radials, directly attached to the belt, and bone rays. The belt of the anterior pair of limbs consists of small, chondral origin of coracoids (coracoideum) and “shoulder blades” (lamina perforata). To these chondral bones that make up the primary belt, the skin bones of the "secondary" belt join. The main one is the large crescent-shaped cleitrum, which, through smaller bones, articulates with the brain part of the skull.

The skeleton of the ventral fins consists only of cutaneous bone rays. The belt of the hind limbs lies in the thickness of the muscles and is represented by a pair of elongated plate.

Thus, it can be seen that the skeleton of paired limbs in bony fishes is compared with the skeleton of paired limbs of cartilaginous fishes due to the loss of basal fins in both pairs of fins, and radials in the rear pair.

Digestive organs

In most species, the oral cavity is armed with numerous single-apex, conical teeth, which are located not only on the jaw bones: dental, maxillary and maxillary, but also on the palatine, pterygoid bones, on the opener and parasphenoid.

The oral cavity is not clearly delimited from the pharynx leading to the short esophagus. The stomach, of various shapes and sizes, is relatively weakly expressed in some. The intestines are morphologically less differentiated than cartilaginous fish. There is no spiral valve. But at the very beginning of the intestine, many species have its blind processes, sometimes called pyloric. They increase the digestive surface of the intestines and slow down the passage of food, as does the spiral valve in cartilaginous fish. The number of pyloric processes in different fish species is not the same: for perch - 3, for salmon - 40, for mackerel - about 200.

The liver consists of several lobes, equipped with a gall bladder. The bile duct flows into the anterior, loop-shaped section of the intestine. The pancreas is weakly expressed in the form of very small lobules scattered throughout the mesentery.

Respiratory system

Unlike cartilaginous fish, there are no gill walls and gill lobes sit directly on the arches of the same name. There are four complete gills. In addition, on the inner side of the gill cover sits one row of rudimentary petals - the so-called false gill. The act of breathing is carried out by the action of gill covers and mouth, the movements of which cause water to be pumped into the gill cavities and expelled to the outside.

Circulatory system

Most species do not have an arterial cone. The abdominal aorta at the very beginning has a muscular bloating - an arterial bulb - outwardly somewhat similar to an arterial cone, but consisting not of striated, but of smooth muscle. Therefore, this formation is not capable of independent pulsation. Due to the presence of only four pairs of gills, the number of bringing and taking out gill arteries (arterial arches) is four. In the venous system in most species, the continuity of the right cardinal vein is characteristic, and, therefore, only the left cardinal vein forms the portal system of circulation in the corresponding kidney.

Excretory organs

The excretory organs are represented by long ribbon-shaped mesonephric kidneys lying on the sides of the spine above the swimming bladder. The ureters homologous to the wolf canals stretch along the inner edges of the kidneys. Before going out, the ureters are combined into an unpaired canal that opens at the end of the urogenital papilla. Some species have a bladder into which the ureters flow from the dorsal side.

Reproductive organs

The reproductive organs have a different structure than that of cartilaginous fish. Paired testes and ovaries have a cavity inside and open through special channels on the urogenital papilla and separately from the urinary opening. Thus, in females there are no Muller canals serving as oviducts in cartilaginous fish, and in males the testes are not connected with the kidneys and the Wolf's canals act only as ureters.

The caviar is small, with a thin gelatinous shell, fertilized, as a rule, outside the body of the mother. Only a few species have internal fertilization and egg production. Such, for example, are the American subtropical toothy cyprinids (family Cyprinodontidae). One of the most typical species is gambusia, well known for its breeding in aquariums, and in some cases in natural reservoirs. This species is acclimatized and bred in our country in order to destroy the larvae of malaria mosquitoes.

Cases of hermaphroditism are very rare. Permanent hermaphrodite is sea bass (Serranus).

Superorder Bone Ganoids (Holostei)

The most primitive are ray-fin fish, which were widespread in the Mesozoic era. To date, only two species belonging to different orders have survived. The presence of a spiral intestinal valve and arterial cone of the heart is characteristic. Upper occipital bone not developed. The rays supporting the gill membrane are still poorly developed.

Squad Multiple (Polypteriformes)

Mnogoper - a small, but very peculiar group of freshwater fish. The body is covered with large rhombic, movably articulated scales. The dorsal fin consists of a number of small fins, which is why the name of these fish arose. The pectoral fins have a wide fleshy lobe at the base, which externally brings multi-feather fish to cysteras. However, the skeleton of fins in multi-feathers is sharply different.

The swimming bladder is very peculiar. It is double and consists of a large, right and smaller, left departments. These two sections of the bladder communicate with the intestine by a common channel, they serve as an additional respiratory organ. However, unlike bivalves (Dipnoi) and cysterae fishes, multi-feathers do not have internal nostrils.

Multi-feather fish species are common in tropical Africa. They are kept on sections of rivers with a muddy bottom. They eat animal food. Development takes place with transformation. Larvae have very developed external gills.

They have no fishing value.

Currently, just over ten species of multi-species are known. ”No fossils found.

Mnogoperov represent fish specialized in life in tropical ponds, which converged to have some common features with bipedal and tasset fishes: the ability to use air oxygen for breathing, the ability to use paired fins not only for rowing, but also for repelling ponds from vegetation.

Suborder Bony Fish (Teleostei)

Bony fish are the most numerous superorder of bone fish. About 90% of all modern fish belong to it. They are found in all oceans and seas and in fresh water bodies of all continents. In appearance, they are extremely diverse, which is associated with a variety of living conditions and lifestyle. The main common features of the organization are as follows. Scales (if any) are always bony: cycloid or ctenoid. The location of the scales is tiled. Caudal fin homocercal. The skeleton of the pectoral fins does not have basal, and it consists only of radials and skin rays. The skeleton of the ventral fins consists only of skin rays.

There is no arterial cone, the aortic bulb is developed. There is no spiral intestinal valve (with the exception of the few most primitive species). In many, the intestines form blind, the so-called pyloric processes. As a rule, there is a swimming bladder that develops in the form of an outgrowth of the dorsal side of the intestinal tube. In primitive forms, the swim bladder remains in contact with the esophagus for life, while in the majority, the message of the bladder with the esophagus is lost as the fish develops.
There is no single view of the classification of bony fish. The following are their most important groups, which attach importance to the units.

Order Seldeobraznye (Clupeiformes)

The most primitive modern bony fish with a relatively weakly ossified skull and swimming bladder, which remains in contact with the esophagus for life. The rays of the fins are soft, articulated. Scales cycloid. Main families: herring and salmon.

The herring family (Clupeidae) includes a large number of species that live mainly in the seas; some species are included in the rivers for breeding. The following main species are found in our waters. Ocean herring (Clupea harendis) is kept in the White and Barents seas east to Novaya Zemlya and in the seas of the Far East. This species migrates widely in connection with the stages of the life cycle. For spawning herring come to the shores of huge shoals. Spawning occurs in relatively small places. Caviar is heavy, sinks to the bottom and sticks to underwater objects, often to algae. Fertility is significant - from 40 to 280 thousand eggs. Bred off the southwestern coast of Scandinavia, fry drift eastward, carried away by the Atlantic current. Adults after spawning go north for feeding.

The Caspian and Black Seas are rich in herring. Their lifestyle is different. So, the Volga herring (Caspiolosa volgensis) and chernosinka (C. kessleri) ripen and feed during the sea, and for breeding enter rivers and rise over them for hundreds of kilometers. Black spawn after spawning in large numbers dies. The death of the Volga herring after spawning is not so significant. Unlike the previous species, the Caspian pod (C. caspia) usually spends all its life in the sea, but, like the oceanic herring, it migrates widely.

In the Far East, in addition to the oceanic herring described above, the Ivashi sardine (Sardinops melanosticus), close to herring, is widespread. This is a typical marine, widely migrating fish that previously appeared off the coast of Soviet Primorye in spring during feeding.

In the Baltic and Black Seas, sprats (Spratella sprattus) are found, and in the Caspian and Black Seas, kilka (Clupionella delicatula) is close to it. These little fish are close to real herring.

In Russian fisheries, herring occupy the first place.

The family of salmonids (Salmonidae) includes medium and large size representatives of the order being disassembled. They are characterized by the presence on the back of a soft skin fold, the so-called fat fin. The distribution of this group is confined mainly to temperate and northern latitudes. Most salmonids are migratory fish, growing and ripening in the seas, and going to rivers for spawning. The salmon seas of the Far East are especially rich. Chum salmon (Oncorhynchus keta), pink salmon (O. gorbuscha), sockeye salmon (O. nerka), etc. are found here. These fish spawn in the upper reaches of the rivers, and sockeye salmon enter the lakes. The length of spawning migrations is sometimes measured by several thousand kilometers. So, chum salmon only rises up to a distance of 2 thousand km along the Amur. Caviar lays in the holes specially dug by it in the soil in the soil and falls asleep with small pebbles or coarse sand. Juveniles overwinter in the rivers, and in spring rolls into the seas. Adult fish die after spawning, and thus they breed only once in a lifetime. Fertility is insignificant: in chum salmon eggs 3-4 thousand, in pink salmon - 1-2 thousand.

Among real salmon, salmon (Salmo salar), common in the seas of the North Atlantic Ocean, in the Barents and White Seas, should be mentioned. Our salmon comes to spawn in the rivers of the north of the European part of Russia. Spawning migrations occur in summer and autumn. Unlike Far Eastern salmon, not all individuals die after spawning; some individuals breed up to four times in life. Salmon caviar, like Far Eastern salmon, is buried in the bottom soil. In the northern seas, as well as in the Black and Caspian, trout (Salmo trutta) close to salmon is found. It breeds in rivers, but for feeding it does not go far into the sea, and some individuals ripen in rivers. In the rivers there was a dwarf race of brown trout - trout (Salmo trutta fario), which is kept, in addition to rivers, in some mountain lakes.

Among salmon there are also real sedentary freshwater species. Such, for example, whitefish, some omuli and taimen.

axial are of very great commercial importance. Use not only meat, but also caviar, known on sale under the name red.

Weak breeding of salmon and their high value led to the widespread use of measures for the artificial breeding of these fish.

Order Carp-shaped, or bone-bubble (Cypriniformes)

Like herring, these are relatively primitive bone fish, but their ossification of the skull is more developed. The swim bladder communicates with the intestines. The fins are usually soft. There is a Weber apparatus - a system of bones connecting the front of the swimming bladder with the membranous labyrinth of the inner ear. Mostly freshwater, less common migratory fish, in contrast to salmon inhabiting mainly temperate and tropical areas. They live in a wide variety of bodies of water - from mountain rivers to swampy ponds. Most lead a sedentary lifestyle (roach, ide, tench, crucian carp), but some migrate when breeding (roach, ram, cutum). Suborder cyprinids comprise two main families.

Cyprinidae (Cyprinidae) are characterized by the absence of teeth on the jaws and the presence of so-called pharyngeal teeth sitting on the posterior gill arch and serving to fragment the food of the chitinous, or calcareous, coat of animals. These are the most numerous and diverse fish of our fresh water bodies. These include the inhabitant of rivers and lakes roach (Rutilus rutilus), the Caspian-Volga vobla (R. rutilus caspius), the Black Sea ram (R. r. Haeckeli), the river ide (Leuciscus idus), the Volga-Caspian bream (Abramis) brama), common carp (Cyprinus carpio) and its domesticated race - carp, crucian carp (Carassius carassius), tench (Tinea tinea), etc.

Although the taste of meat of cyprinids is worse than that of salmon, the wide distribution and abundance of cyprinids make them the most important fishing group.

Catfish (Siluridae) include fish without real scales, with a serrated mouth. In the way of life, these are predators. We meet two species that inhabit the rivers of the southern half of the country and the coastal parts of the seas. The largest specimens reach 250-300 kg, more often they catch catfish of a smaller size.

Acne Squad (Anguilliformes)

The body is very elongated, serpentine, there are no ventral, and sometimes pectoral fins; anal, caudal, and dorsal fins merge with each other. The swim bladder communicates with the intestines. A small group, distributed mainly in the subtropical and tropical zones. Among eels there are marine and migratory species. We meet river eel (Anguilla anguilla), distributed mainly in the Baltic Sea basin. It is biologically interesting in that it spawns from rivers to the Atlantic Ocean to the West Indies, where it breeds at great depths. Larvae migrate back to the rivers, making this journey at about 4 years old.

Pike-like squad (Esociformes)

A small group of predatory fish with strongly elongated jaws, which are armed with sharp teeth. As with previous units, the swim bladder communicates with the intestines. Common pike (Esox lucius) is common in our rivers, lakes, and in desalinated areas of the southern seas. The lifestyle is sedentary. It usually keeps among thickets of aquatic vegetation. It feeds on fish, chicks, and frogs. When fish farming is very harmful. The fishing value is small. Large specimens reach a mass of more. 35 kg and a body length of more than 1.5 m. Spawns in the spring in shallow water in the coastal zone.

Order Perch (Mugiliformes percesoces)

A small group of fish with a closed swimming bladder and without a lateral line, living mainly in the southern seas. In our Black and Azov Seas, the family of mullet (Mugilidae) is widespread. The main commercial value is loban, or common mullet (Mugil cephalus), and singil (M. auratus). Mullet - herd and nomadic fish.

Large shoals of them go in search of food into the lagoons, saline lakes and estuaries where they are mined. Recently, mullet has been successfully acclimatized in the Caspian Sea.

Sargan Squad or Flying Fish (Beloniformes)

Peculiar, often marine, fish that can jump far out of the water, and some soar over water for a considerable distance. Of particular interest in this regard are the long-tailed feathers (Exocoetus), which have very large pectoral fins. Using them, fish jump out of the water and fly about 150-200 m in a planning flight. They are distributed mainly in tropical seas. We found near Vladivostok.

Squad-like squad (Gasterosteformes)

Small fish, in which the front of the dorsal fin is turned into sharp spikes, and the ventral fins in the form of sharp spikes. Scales in the form of bone scutes. They live in fresh and brackish waters of the northern hemisphere. Interesting in that eggs are laid in a nest made of plants. The female tosses only about 100 eggs. We have several species of sticklebacks common in the Baltic, Barents, Black, Azov, Caspian seas and in some rivers.

Squamous gill squad (Lophobranchii)

A very peculiar group of small sea fish. Gills are reduced to small bundles attached to rudimentary branchial arches. The body is covered with annular bone plates. Head with a long tube-shaped snout, mouth small, toothless. Males have special brood pouches on their belly, in which they carry fertilized eggs. Distributed mainly in warm and tropical seas. Represented by seahorses (Hippocampus) and sea needles (Syngnathus). We meet in the Black, Caspian, Baltic and Japanese seas. They have no fishing value.

Thistle Squad (Acanthopterarygii)

An extensive group of quite diverse marine and freshwater fish, in which part of the rays of the fins looks like undifferentiated sharp spikes. The ventral fins are usually located under the pectoral, and sometimes in front of them. The swim bladder does not communicate with the intestines.

Perch (Percidae) include most of the species of this order, many of which are of great commercial importance. Among our representatives, we should mention zander (Lucioperca), several species of which live in the basins of the Black and Caspian Seas. Some of them constantly live in rivers, others in the seas, and others are semi-migratory fish that go for feeding from rivers to the seas. Large individuals reach a mass of 10-12 kg. They are of great commercial importance. Perches (Perca) are widespread in the rivers and lakes of our country. They have a settled lifestyle. They reach a mass of 1 kg, rarely more, and a length of 50 cm. In some places they are important objects of fishing. Ruffs (Acerina) have no commercial value.

Peculiar labyrinths (Anabantidae) are characterized by the presence of saccular outgrowths of the gill cavity, which serve for temporary breathing air. These fish, for example pineapple (Anabas testudineus), often crawl ashore, climb trees. They live in fresh and brackish water bodies of tropical Africa, Asia and the islands of the Malay archipelago.

Mackerel (Scombridae) - marine, mainly tropical, fish that inhabit the water column of the open parts of the sea. We have several species common in the Baltic and Black Seas. They migrate widely. An important subject of fishing (especially in the Black Sea).

Tuna (Thunoidae) are systematically close to mackerel, and some taxonomists include them in the same family. Their sizes vary from 40 cm to 3 m. They are common in coastal and open waters of the World Ocean to the north to the coast of Scandinavia and to the south to the southern tip of Africa and Australia. In the Black Sea, tuna (Thunnus thynnus) can be found over the years. Very energetic swimmers, capable of speeds up to 90 km / h. Probably, in this regard, the lateral musculature of their body has an exceptionally strongly developed system of blood vessels that feed this muscle.

Tuna is an important fishing target.

Goby (Gobiidae) - small, often coastal marine, rarely freshwater fish. Benthic lifestyle, fed by bottom invertebrates. In some species, males during breeding arrange nests for laying eggs, which they guard. We distributed mainly in the southern seas and rivers. In the Black, Azov and Caspian regions they are fishing objects.

Cod Squad (Gadiformes)

A very important fishing group. Usually large fish with soft rays of fins. Distributed in temperate and arctic seas, only burbot (Lota lota) - freshwater fish. Many species enter the estuarine desalinated areas of the sea and even rivers, such as, for example, saffron cod, Arctic cod, polar cod. The lifestyle is predominantly bottom-line.

Of greatest commercial importance is cod (Gadus morbua), common in our Baltic, Barents, White Seas and in the northern seas of the Far East. There is no cod off the coast of Siberia (with the exception of occasionally observed calls from the Barents Sea to the Kara Sea). Cod migrates widely. Its spawning occurs mainly at the Lofoten Islands, to a lesser extent off the coast of the Kola Peninsula. After spawning, cod goes to the eastern part of the Barents Sea, where it feeds on banks (elevated sections of the seabed). Here it is mined by trawls - special bottom seines. Cod is the main object of trawl fishing in our country (up to 85% of the total trawl catch). Cod has great fecundity; it flies from 2.5 to 10 million eggs. In addition to cod, we must mention haddock (G.aeglefinus), pollock (Pollachius virens), polar cod (Boreogadus saida), which also serve as important objects of our trawl fishery in the northern seas. In the extraction of cod fish, not only meat is used, but also liver fat, which is very rich in vitamin D and is known as medical fish oil.

In our northern seas and the Far East, navaga (Eleginus navaga) is common. In winter, it often goes to the mouths of the rivers, where it is mined.

The only valuable freshwater species of the detachment under consideration is the burbot (Lota lota), which inhabits the rivers of Eurasia and North America.

Flounder Squad (Pleuronectiformes)

The body is strongly compressed from the sides, the eyes are located not on the sides of the head, but on one side of it. There is no swimming bladder. Bottom fish lie and swim on their sides. The “upper” side of the fish is pigmented, the “lower” side is usually white. Flounder larvae initially swim in the water column, but subsequently, as they move to the bottom lifestyle, the body flattenes in the lateral direction, and the eyes move to one of the sides of the body - the “upper” one. Several dozen species are widely distributed across the seas of the globe. We are found everywhere in the seas (except for the Caspian and Aral). Flounders migrate relatively little, their movements associated with the choice of places for spawning, wintering and with the search for food, usually do not exceed 100-200 km. They often spawn near the coast or on banks. Fertility is very large - up to several million eggs. They feed on bottom invertebrates. An important object of trawling.

Detachment Maxillary (Plectognathy)

A small group of marine, mainly tropical, fish, anatomically characteristic in that the intermaxillary and upper jaw bones are fused, forming a strong "beak". The teeth are massive, chisel-shaped or lamellar adapted for crushing the shells of mollusks and crustaceans. The body is covered with large scales or bone plates. Some species live in the surf zone, and the bone shell seems to be a device that protects the body from shock waves. Typical species: pufferfish (Tetrodon hispidus), boxfish (Ostracion quadricornis).

Order Feet (Pediculati)

A small group of bottom fish with a body somewhat flattened in the dorso-abdominal direction, and heavily altered rays of the pectoral fins, which look like flippers and serve to move along the bottom. In our Black and Barents Seas, a monkfish (Lophius piscatorius) is found. The front rays of the dorsal fin are turned into long, movable tentacles. It is believed that the oscillatory movements of the tentacles attract small fish, which are caught by a monkfish, hiding at the bottom, in thickets of algae.

General characteristics

Bivalves are a small ancient and very peculiar group of freshwater fish combining primitive traits with traits of high specialization for life in oxygen-depleted bodies of water. So, most of the skeleton of modern representatives remains cartilage for life. A well-developed chord is preserved. The vertebral column is almost not developed and is represented by the rudiments of the upper and lower arches of the vertebrae. Skull based on cartilage, with few integuments. There are no maxillary and intermaxillary bones. Like cartilaginous fish, there is a spiral valve in the intestines and a pulsating arterial cone in the heart. All these are features of a primitive organization.

Along with this, in double-breathing fish, non-square cartilage grows directly to the skull (austilia). Paired fins of a biserial type. Bone scales. Caudal fin difficercal. Finally, the most remarkable feature of bipedal breaths is the presence, in addition to the gill, of pulmonary respiration. As organs of pulmonary respiration, one or two blisters function, opening on the ventral side of the esophagus. These formations are apparently not homologous to the swimming bladder of bony fish. Through nostrils, serving for pulmonary respiration. Blood enters the lungs through special vessels extending from the fourth pair of efferent gill arteries. These vessels are apparently homologous to the pulmonary arteries. From the "lungs" come special vessels that carry blood to the heart, which can be considered homologues of pulmonary veins. In the atrium there is a small septum, partially dividing it into the left and right halves. Blood from the pulmonary veins enters the left part of the atrium, all the rest of the blood comes from the Cuvier ducts and from the posterior vena cava to the right. It should be emphasized that the vena cava is absent in previous subclasses of fish (except multi-feather) and that this vessel is characteristic of terrestrial vertebrates. The vena cava arises by splitting the right cardinal vein.

The progressive signs of bivalves also include the strong development of the forebrain, whose roof is not epithelial, as in bony fishes, but contains nerve cells. Finally, the genitourinary system is close to that of cartilaginous fish, on the one hand, and amphibians, on the other.

So, the oviducts are the Muller channels that open into the body cavity. There are no independent vas deferens, and the Wolffian canals enter the genital tract, into which the vas deferens enter the tubules, which initially passed through the anterior section of the mesonephric kidney.

Squad One-lung (Monopneneumones)

Contains one family Ceratodidae with one modern genus Neoceratodus. The representative is neoceratode (N. forsteri). This is the largest of modern breathing fish, reaching a length of 175 cm. Distributed in East Australia in the Queensland rivers. The structure is characterized by the presence of an unpaired pulmonary sac, not completely divided into two symmetrical halves. Gills are well developed. Neoceratode can breathe both at the same time gills and lungs, and individually each of them. In this regard, he can live in heavily overgrown reservoirs, where other fish cannot exist. In the summer, when water, due to their drying out and decay of plant debris, is very depleted of oxygen, the neoceratode breathes predominantly or even extremely light.

Fish often rises to the surface of the water and swallows air, making a loud, splashing sound at this time. In the fall, as the reservoirs fill with fresh water, the value of pulmonary respiration decreases, and often blood oxidation is provided by passing it only through the gills. Neoceratodes live in perennial reservoirs and do not hibernate. They are kept in the bottom layers of water, often lie at the bottom. They feed on crustaceans, mollusks and worms. They breed more often in September and October. Eggs are laid among aquatic plants. Development takes place without transformation, and fry do not have external gills.

Two-pulmonary squad (Dipneumones)

Two very close families are included: Protopteridae, common in tropical Africa, and Lepidosirenidae, common in South America, in the Amazon. The first family includes several species of the genus Protopterus (Protopterus), the second - one genus and the species - lepidosiren (Lepidosiren). Bipulmonary is characterized by the presence of a paired lung, partial reduction of the gills. The value of pulmonary respiration is noticeably greater than gill. These fish cannot do without pulmonary respiration even when the water is rich in oxygen.

The weak development of paired fins, which have the appearance of thin bundles, is also characteristic. The size is smaller than that of a neoceratode: for lepidosiren - up to 125 cm, for protopterus - up to 140 cm.

They live in rivers and in shallow marshes, sometimes completely dry. When the pond dries, the protopterus burrows in the mud of the bottom and is encapsulated. Lepidosiren does not form capsules. Summer hibernation lasts about 5 months. Under artificial conditions, the protopterus is able to stay hibernated for 3-4 years. During hibernation, breathing is only pulmonary. Air passes through passages in the bottom soil to the mouth or nostrils and further to the lungs. With the onset of the rainy period, the fish awakens. It feeds on bottom invertebrates and partially plants. Caviar lays in holes or in minks at the bottom. Development with transformation. Larvae possess external gills, which remain in a rudimentary state and in an adult protopterus.

Breathing do not have significant industrial value. They are caught by local residents for personal consumption. These fish are interesting mainly because, although they are not the ancestors of terrestrial vertebrates, they nevertheless have a number of common features with them. A study of the structure and lifestyle of the bipedal breathing makes it possible to imagine a likely way of transforming fish into amphibians.

Subclass Wormfishes (Crossopterygii)

An ancient and almost completely extinct group of peculiar fish. Cysterae had a relatively wide distribution in the Devonian and Carboniferous; in the Mesozoic, the number of species and the latitude of distribution decreased.

Not so long ago, it was believed that at present there are no bristles. The first specimen of these amazing fish was obtained in 1938 in the Indian Ocean, off the southern coast of Africa, near the mouth of the Halumna River, at a depth of about 70 m. It was a large fish - 150 cm long and 57 kg in weight. It was called Latimeria (Latimeria chalumnae). Despite a thorough search, it was only in 1952 that it was possible to get the second modern cysterae fish belonging to the same species. The place of its prey is also the Indian Ocean, near the island of Anjouan (12 ° 15 'S and 44 ° 33' E), 200 m from the coast at a depth of about 15 m. Fish length 139 cm. Subsequently, in this The area has been repeatedly caught by brushfish.

Modern tasseteri - coelacanths, or coelocants, were found only in the area of ​​the Kamor Islands, where they are kept at a depth of 400-1000 m at a water temperature of 10-14 ° C. Light is clearly avoided, which is found in the natural environment and when keeping caught fish in half-flooded boats . Coelocants are predators, and their mouths are armed with sharp teeth. The body length of sexually mature individuals is 125-180 cm, weight 25-80 kg. The vertebrae are embryonic, and the chord is well developed for life. The primary skull is largely cartilaginous.

A large degenerated lung filled with fat was found in the body cavity. The coelacanths have no internal nostrils, and they, unlike the Mesozoic cysteras, are not capable of breathing atmospheric oxygen. Pisteraces are interesting in that they represent the branch of fish from which the amphibians evolved. As well as for double breathers, they were characterized by double breathing - not only gill, but also pulmonary. This is indirectly indicated by the presence of many extinct nostrils in many extinct species. However, modern marine brush-like open nostrils do not.

Paired fins have a very peculiar device. At the base of them is a wide fleshy lobe, inside of which there is a skeleton of the main part of the fin itself. Thus, the muscles of the limb are located in them, as in terrestrial vertebrates, on the freest limb, and not only on the body, like other fish. The skeleton of the fin in some bristles is surprisingly reminiscent of the skeleton of a five-fingered limb. The fin base is supported by one element (b azalea), in which the homologue of the humerus can be seen. Next come two elements (also basal), corresponding to the radius and ulna bones. Finally, even further to the periphery is a series of rays (radials) corresponding to the brush.

The body is covered with cosmoid scales, representing thick bone plates of a round or rhombic shape, coated on top with a cosmic (modified dentin) and a thin layer of enamel.

It is important to take into account that the presence of skin ossifications, from which a bone carapace was formed on the body, was also characteristic of primary amphibians. Finally, it is necessary to indicate the presence of a splatter in the cysteper fish - a residual visceral gap, which in amphibians turns into a cavity of the middle ear.

Pisteraids are undoubtedly close to bipedal and arose, apparently, from one root. They originally lived in fresh water bodies, in which oxygen deficiency was probably periodically observed. In this regard, double breathing developed: with a lack of oxygen for the fish, these, like modern breeders, rose to the surface of the water and swallowed air. The clogging of reservoirs by growing and dead vegetation was apparently a prerequisite for the development of the described peculiar paired limbs, which, due to the presence of muscles on the limb itself and the dissection of the skeleton, could be used not only for rowing, but also for support on a solid substrate, for example, stems and trunks plants bottom. In turn, this was a prerequisite for the transformation of such fins into five-fingered limbs. Having arisen in fresh waters, subsequently, the brush-headed fish came to life in the sea. The remnant of this group of brushworms is modern coelacanth.

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