There are 2 classes of fish: the cartilaginous class and the bony class.

Class Cartilaginous fish. Cartilaginous fish include sharks and rays. They have a cartilaginous skeleton. The skin of most species is covered with scales with tooth-like spikes covered with enamel. The gills open outward with 5-7 gill slits. There is no swim bladder.

Sharks live mainly in the water column. Most of them are predators. The head of sharks ends in an elongated snout - the rostrum. The mouth is located on the underside of the head and looks like a transverse slit. Jaws with several rows of sharp teeth. A torpedo-shaped body and a powerful unequal-bladed tail fin enable sharks to develop high speed.

Stingrays have a flattened, usually disc-shaped body. Their skin is bare or covered with spines. The edges of the pectoral fins are fused with the sides of the head and body. The dorsal fins are shifted to the tail or are absent altogether. Most stingrays lead a bottom-dwelling lifestyle. They feed mainly on mollusks.

The class Bony fishes unites most species of fish, which are divided into osteochondral fishes, lungfishes, lobe-finned fishes and bony fishes.

Osteochondral, or sturgeon, fish (beluga, sterlet, Russian sturgeon) have an osteochondral skeleton with a developed notochord, gill covers, and a swim bladder. There are 5 rows of bone plates running along their body, and small plates between them. Head with an elongated snout. Mouth on the underside of the head. The caudal fin is unequally lobed. Sturgeon migratory fish of water bodies of the Northern Hemisphere. They are widely known for their especially tasty meat and black caviar.

Lungfishes (6 species in total) are an ancient group of fish. These include the Australian cattail, African and South American lepidoptera. These fish retain the notochord and do not develop vertebral bodies. Along with gills, they have lungs that developed from the swim bladder.

Lobe-finned fish are an ancient group of fish. Their skeleton was mainly cartilaginous and had a notochord. The lobefin's fins looked like fleshy blades, and the swim bladder turned into a pair of lungs. Until the 20th century were considered extinct. One is currently known modern look coelacanth, a descendant of sea lobe-fins.

Bony fishes are the most numerous group modern fish(about 96% of all species). Their skeleton is ossified, the notochord develops only in the embryo, the scales are bony, and the swim bladder is common. These fish live in almost all bodies of water on Earth. This group includes the orders of herrings (herrings, sardines, anchovies, two species of which are called anchovy), salmonids (red salmon, or salmon, chum salmon, pink salmon, Chinook salmon), cyprinids (chub, bream, ide, asps, carp, crucian carp), catfish (catfish), cod (cod, haddock, blue whiting, pollock, burbot), flounder (flounder, halibut). There are more than 40 units in total.

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Teleost group Contains about species. Representatives of crucian carp, burbot, perch, pike, herring, salmon. The body is covered with small scales. There is one pair of gill slits; there are gill covers. There is a swim bladder. The skeleton is bony.

1. Of the listed signs, designated Arabic numerals, write which of them are typical for the classes: I. Cartilaginous fish II. Bony fishes III. Cartilaginous fishes IV. Lungfishes V. Lobe-finned fishes 1. Adapted to living in dry, oxygen-depleted water bodies 2. The notochord is preserved throughout life 3. Scales in the form of large bony plaques 4. The skull is cartilaginous 5. The spine is bony, consisting of the trunk and caudal sections 6. The fins are arranged horizontally 7. The brain skull is cartilaginous, covered on the outside with bones 8. Gill cover 9. Swim bladder 10. Most of the skeleton is cartilaginous 11. One or two bladders in the esophagus 12. Hibernates 13. Rudimentary vertebrae 14. Lives in shaded bodies of water 15. Fleshy fins 16. Gill covers absent 17. The caudal fin has two unequal lobes 18. The body is covered with scales 19. The scales are protected by mucus

Pisces class- this is the largest group of modern vertebrates, which unites more than 25 thousand species. Fish are inhabitants aquatic environment, they breathe with gills and move with the help of fins. Fish are distributed in different parts of the planet: from high mountain reservoirs to ocean depths, from polar waters to equatorial ones. These animals inhabit salt waters seas, found in brackish lagoons and estuaries large rivers. They live in freshwater rivers, streams, lakes and swamps.

External structure of fish

The main elements of the external structure of the fish’s body are: head, gill cover, pectoral fin, pelvic fin, trunk, dorsal fins, lateral line, caudal fin, tail and anal fin, this can be seen in the picture below.

Internal structure of fish

Fish organ systems
	1. Skull (consists of the braincase, jaws, gill arches and gill covers) 2. Skeleton of the body (consists of vertebrae with arches and ribs) 3. Skeleton of fins (paired - pectoral and abdominal, unpaired - dorsal, anal, caudal)	1. Brain protection, food capture, gill protection 2. Protection of internal organs 3. Movement, maintaining balance
Musculature	Wide muscle bands divided into segments	Movement
Nervous system	1. Brain (divisions - forebrain, middle, medulla oblongata, cerebellum) 2. Spinal cord (along the spine)	1. Movement control, unconditioned and conditioned reflexes 2. Implementation of the simplest reflexes, conduction of nerve impulses 3. Perception and conduction of signals
Sense organs	3. Hearing organ 4. Touch and taste cells (on the body) 5. Lateral line	2. Smell 4. Touch, taste 5. Feeling the direction and strength of the current, the depth of immersion
Digestive system	1. Digestive tract (mouth, pharynx, esophagus, stomach, intestines, anus) 2. Digestive glands (pancreas, liver)	1. Capturing, chopping, moving food 2. secretion of juices that promote food digestion
swim bladder	Filled with a mixture of gases	Adjusts immersion depth
Respiratory system	Gill filaments and gill arches	Carry out gas exchange
Circulatory system (closed)	Heart (two-chambered) Arteries Capillaries	Supplying all body cells with oxygen and nutrients, removing waste products
Excretory system	Kidneys (two), ureters, bladder	Isolation of decomposition products
Reproduction system	Females have two ovaries and oviducts; In males: testes (two) and vas deferens

The figure below shows the main systems of the internal structure of fish

Fish class classification

Living fish today are divided into two main classes: cartilaginous fish and bony fish. Important distinguishing features of cartilaginous fish are the presence of an internal cartilaginous skeleton, several pairs of gill slits that open outward, and the absence of a swim bladder. Almost all modern cartilaginous fish live in the seas. Among them, the most common are sharks and rays.

The vast majority of modern fish belong to the class bony fish. Representatives of this class have an ossified internal skeleton. A pair of external gill slits are covered with gill covers. Many bony fish have a swim bladder.

Main orders of Pisces

Orders of fish	The main characteristics of the detachment	Representatives
	Cartilaginous skeleton, no swim bladder, no gill covers; predators	Tiger shark, whale shark, katran
	Manta ray, stingray
Sturgeon	Osteochondral skeleton, scales - five rows of large bone plates, between which there are small plates	Sturgeon, beluga, sterlet
Dipnoi	They have lungs and can breathe atmospheric air; the chord is preserved, there are no vertebral bodies	Australian cattail, African scalefish
lobe-finned	The skeleton mainly consists of cartilage, there is a notochord; poorly developed swim bladder, fins in the form of fleshy outgrowths of the body	Coelacanth (the only representative)
Carp-like	Mostly freshwater fish, there are no teeth on the jaws, but there are pharyngeal teeth for grinding food	Carp, crucian carp, roach, bream
Herring	Most are schooling sea fish	Herring, sardine, sprat
cod	A distinctive feature is the presence of a mustache on the chin; the majority are cold-water marine fish	Haddock, herring, navaga, burbot, cod

Ecological groups of fish

Depending on their habitat, ecological groups of fish are distinguished: freshwater, anadromous, brackish and marine.

Ecological groups of fish	Main features
Freshwater fish	These fish constantly live in fresh water. Some, such as crucian carp and tench, prefer standing water. Others, such as the common gudgeon, grayling, chub, have adapted to life in flowing waters rec.
Migratory fish	This includes fish that move from sea water to fresh water to reproduce (for example, salmon and sturgeon) or from fresh water go to reproduce in salt water (some types of eels)
Salty fish	They inhabit desalinated areas of the seas and the mouths of large rivers: such are many whitefish, roach, goby, and river flounder.
Sea fish	They live in the salty water of seas and oceans. The water column is inhabited by fish such as anchovy, mackerel, and tuna. Stingrays and flounder live near the bottom.

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A source of information: Biology in tables and diagrams./ Edition 2, - St. Petersburg: 2004.

Taxonomy of fish.

Lecture 2

Biological features fish Biotic and abiotic

connections between fish and external environment. Ecological groups of fish

Taxonomy of fish.

The foundation of all biological sciences is taxonomy, the basic unit of which is the species. The scientific name of a species is indicated by two Latin words: generic and specific. Usually after the double name the surname of the author is given and the year of description of this species is indicated.

Aquatic fish vertebrates. This is a thriving group of animals, distributed in marine and freshwater bodies and numbering more than 20 thousand species. Fish are very variable and often form subspecies. And so the basic unit of taxonomy is the species. Species are united into genera, genera are united into families, families are united into orders, orders are united into classes, classes into types. For example: the roach, belonging to the genus Rutilus, is part of the family Cyprinidae (cyprinidae), order Ciprininiformes (cyprinids), which is in the class Osteichties (bony fish) of the phylum Chordata (chordates). There are also intermediate taxa: Superclasses, Suborders of subfamilies

The superclass of fish is divided into three classes: cyclostomes, cartilaginous fish and the class of bony fish.

Cartilaginous animals include mainly sharks and rays.

They are characterized by primitive features: the skin is covered with placoid scales formed by dentin and covered on the outside with enamel. Placoid scales extend into the oral cavity and cover the jaws, acting here as teeth. The structure of teeth in mammals is basically the same, i.e. these formations are homologous in cartilaginous fish and mammals.

The skeleton is cartilaginous. The spine consists of two sections: trunk and caudal. The notochord is preserved inside the vertebral bodies. They also do not have a swim bladder, why do sharks have to be constantly on the move?

Along with primitive features, cartilaginous fish also have a number of progressive features: they have a relatively large brain, well-developed olfactory organs, eggs contain a large amount of yolk, and some species are viviparous.

The vast majority of fish belong to the bony class. They appeared in the Devonian. At this time and later, lungfishes and lobe-finned fish, they gave rise to amphibians.

The class of bony fishes includes four subclasses:

1.Chondrostei (sturgeon)

2. Ray-finned fish (Actinopterigii), (herring, salmon, carp, eels, perch, pike, stickleback, flounder, etc.)

3. Lungbreathers (Dipnoi). (protopterus)

4. Crossopterigii (coelacanth)

Currently, about 25 thousand species of modern fish are known.

Skeleton bony fishes are formed by bones, but in some primitive species(a subclass of cartilaginous bones, which includes sturgeon fish) along with bones, there are also cartilaginous elements of the skeleton. The skeleton consists of the spine, cranium, visceral skeleton and limbs (paired fins and their girdles). The spine is divided into trunk and caudal sections. The ribs articulate with the transverse processes of the vertebral bodies. The bony rays of the fins are attached to the bones of the limb girdles.

The body of fish is divided into head, body and tail. The lifestyle of fish affects their appearance. There are about 12 different morphological types. The most common: torpedo-shaped– best swimmers such as herring, cod, tuna, serpentine– (acne), ribbon-like– relatively poor swimmers – saber fish, herring king, swept(capable of sharp acceleration, many predators) pike, taimen, flattened - body symmetrically compressed laterally like a bream or asymmetrically compressed like a flounder (they are poor swimmers), spherical (body)

The body and tail sections have leathery outgrowths with bony rays - fins. They can be paired (thoracic, abdominal) and unpaired - dorsal, caudal, anal. They perform the function of movement and steering, supporting the body in the desired position. The caudal fin is the main mover of the fish. Its shape can be different: symmetrical, heterocercal - asymmetrical and false symmetrical. Fish move thanks to the movements of the caudal fin. Paired limbs: the pectoral and pelvic fins serve as depth rudders. Some fish are capable of jumping out of the water and flying over 200-400m (flying fish).

External covers of fish formed by multilayered squamous epithelium (epidermis) and connective tissue dermis. The epithelium contains numerous unicellular glands that form mucus. Mucus coats the fish's body and helps reduce friction when swimming. Mucous cells secrete species-specific substances that allow fish to recognize each other from a distance. These secretions differ not only among individual species, but also among different sexes and ages. In the mucus secretions of injured fish, scientists identified the substance ichthyopterin, which is called the substance of fear. In some species of fish, the mucus is toxic, sometimes there are large poisonous glands - these are also derivatives of the epidermis, like the luminous organs of many deep sea fish. IN lower layers The epidermis contains chromatophores (melanophores) - stellate pigment cells. The pigment can have different colors, which determines the color of fish, the presence of spots and stripes. Thanks to pigment cells, fish can change body color depending on the background of the environment, which is why fish are so colorful. Fish easily change color intensity depending on the soil and light.

The skin of fish is covered with scales - these are bone scales located in the corium. The shape of scales in fish varies: ganoid (the most primitive, covered with a dentin-like substance), cycloid - has a smooth edge (in cyprinids, whitefishes) and ctenoid (the outer edge has denticles) - in perciformes. The scales grow unevenly throughout the year, so growth rings form on them, which can be used to determine the age of the fish. In bony fishes, the integumentary bones of the skull and the girdle bones of the forelimbs are formed in the dermis. The outer layer of the epidermis becomes keratinized. During the spawning period in species such as whitefish and carp, the degree of keratinization increases and a pearl rash appears.

central nervous system includes the brain and spinal cord. The brain consists of five sections, of which largest sizes reaches the midbrain and cerebellum. The spinal cord is located in the canal formed by the upper arches of the vertebrae.

Great importance In life, fish have sensory organs that allow them to navigate in space.

The eyes are located on the head - they have a round lens and a thickened cornea, which allows them to distinguish objects at a short distance of 10-15 m. The organs of smell and taste are of much greater importance, i.e. chemical sense organs. The importance of these organs for orientation in space and choice of direction is demonstrated by the fact that taste buds are located not only in the mucous membrane lining the oral cavity, but also in various areas of the skin and on the fins. The extremely high sensitivity of the chemical sense organs allows fish to migrate to spawning sites over distances of thousands of kilometers (eels, salmon). In front of the eyes there are olfactory openings, but not on the lower side like in sharks, but on the upper. Sturgeons have one more hole - the squirter. The gill arches are located in the gill cavity and are covered with gill covers.

Fish are characterized by lateral line organs. They are groups of sensitive cells arising from the ectoderm, equipped with cilia and located at the bottom of grooves or in channels communicating with the external environment through openings. The channels of the lateral line organs stretch along the body and perceive water vibrations, the speed and direction of currents, and the presence of objects in the path of the fish’s movement. The accuracy of such orientation is great: the blinded fish swam without bumping into objects and grabbed prey. Fish can also perceive fluctuations in the strength of magnetic and electric fields, and sound vibrations.

Organ of hearing and balance in fish consists of an inner ear, consisting of three semicircular canals (the organ of balance), and a hollow sac that perceives sound vibrations. Fish themselves are capable of making sounds that serve as signals when searching for food, during reproduction, etc. These sounds are creaking, clicking, and groaning that occur when teeth rub, joints between bones, or when the volume of the swim bladder changes. The ear labyrinth is used to determine the position of the body in space. A system of bone canals located in three mutually perpendicular planes. In the canals there are otoliths, or large ear stones, which press on one or another part of the labyrinth and by the pressure the fish knows where the bottom is.

Vision in fish it is colored. Fish are myopic, clearly distinguish objects at a distance of 1 m, and up to a maximum of 15 m. The fish perceives infrasound and sound vibrations, as well as mechanical movements of water. Fish perceive water currents and vibrations with a frequency of 5-25 Hz by the organs of the lateral line, and with a frequency of 160-13000 Hz by the lower part of the labyrinth. The swim bladder also participates in the perception of sound as a resonator. Fish make sounds reminiscent of drum beats, grunting, grinding, croaking, whistling, and grumbling. Some sounds have a signal value, and some are formed during movement, nutrition

swim bladder- a derivative of the digestive tube, found in most bony fish. It arises in the embryonic period of development as a growth on the dorsal side of the intestine. Depending on whether the connection between the bladder and the esophagus is maintained, fish can be open-vesical or closed-vesical. In some species of fish, the bladder, through a group of small bones, is connected to the membranous labyrinth of the inner ear, which allows the fish to perceive impulses from the swim bladder, which changes its volume when changing the position of the body in space. The connection between the bladder and the balance organ is called Weber's apparatus. The swim bladder is filled with air, which significantly reduces the specific gravity of the fish and allows it to float in the water. Fish can arbitrarily change the volume of gas in the bubble, which leads to a decrease or increase in buoyancy. For this purpose, closed-vesical fish have a special network of blood capillaries that absorb or release gas depending on the need of the fish. Only good swimmers, such as mackerel or bottom-dwelling species, lack a swim bladder

Digestive system consists of : from the digestive tract and digestive glands. The digestive tract is divided into: the oral cavity, pharynx, stomach, small and large intestine. The position of the mouth opening depends on the way the fish feeds. In planktivorous fish, the mouth occupies the upper position, in predators it is terminal, and in benthivorous fish (picking up food from the bottom) it is lower. There are also transitional options. Some species have a retractable mouth, which allows them to rummage through muddy soil in search of food (carp). The oral cavity is equipped with numerous teeth that bear whole line bones of both parts of the skull (cerebral and visceral): maxillary, premaxillary, dental bones - all these bones belong to the jaw apparatus, palatines, vomer and copula of the hyoid arch. All teeth are of the same type and inclined towards the pharynx, so fish can only hold prey, or tear off pieces from it, like a piranha, but cannot chew it. Usually the teeth grow into the bone, sometimes they are attached movably. The basis of the tooth is dentin, covered on the outside with a thin layer of enamel. Throughout life, worn teeth are replaced with new ones. U peaceful fish There are no teeth in the oral cavity. Both bony and cartilaginous fish lack a true tongue. Instead, there is a fold of the mucous membrane, devoid of its own muscles and therefore cannot move forward. Some fish species may have teeth on it.

The pharynx of fish is penetrated by gill slits and is actively involved in the feeding process. The entry of food into the mouth often occurs due to the movement of the gill covers, while water along with food is sucked into the oral cavity, passes from it into the pharynx and is pushed out of it through the gill slits. In this case, the food remains in the pharynx, since the gill rakers located on the gill arches do not allow it to pass through. The structure and number of gill rakers depends on the feeding pattern of the fish. In planktivores, these formations are numerous and long, and together they form a filtration apparatus. In predators they are few or not developed at all. Benthos-eating (cyprinid) fish have wide pharyngeal teeth on the fifth gill arch that grind food. Salivary glands are absent in fish.

The short esophagus leads to the stomach, which is not anatomically expressed in all fish. It is absent in carp fish and some gobies. The stomach passes into the small intestine, and the ducts of the liver and pancreas flow into its initial section. It is here that most of the high molecular weight compounds in food are broken down and absorption occurs. The small intestine forms loops and the first of them is called duodenum. Many species of fish have pyloric appendages at the border between the stomach and small intestine, in which proteins are broken down and amino acids are absorbed. Pyloric appendages increase inner surface

Guts 3.2 times. The number of appendages varies from 3 in perch to 400 in salmon.

Liver, forms two or three lobes; in cyprinids the number of lobes can reach 7 and is located in the intestinal loops. Bile enters gallbladder and enters through a special duct into the cavity of the small intestine. Bile performs two main functions: it activates lipase and emulsifies fats contained in food (that is, it crushes large fat droplets to the smallest droplets). The liver not only actively participates in digestion, but also neutralizes toxic substances, which are contained in the portal vein flowing from the organs digestive system venous blood, and also normalizes the concentration of monosaccharides in this blood. In addition, reserve nutrients are deposited in the liver. A lot of fat is stored there, it is very rich in vitamin A. Excellent canned food is obtained from the liver of cod and sharks. Since cartilaginous fish do not have a swim bladder, the large liver of these fish contributes to their buoyancy. In fish that starve for a long time, the liver is greatly reduced in size. The pancreas of sharks is an anatomically formed structure that is located in the mesentery of the small intestine. In higher bony fishes, the pancreas is anatomically absent; it is represented by the islets of Langerhans in the liver. It performs exocrine and endocrine functions. As exocrine, it secretes digestive enzymes - trypsin, amylase, maltase, lipase, etc., which enter the cavity of the small intestine through the ducts. As an endocrine gland, the liver synthesizes some hormones that enter the blood.

The small intestine passes into the large intestine, which is externally indistinguishable from the small intestine. Sturgeons, lungfishes, have a spiral valve. It is absent in higher bony fishes. The total length of the digestive tract varies greatly depending on the type of diet. In herbivorous fish, the digestive tract is much longer (in silver carp it is 6-15 times longer than the body length) than in omnivores. It is shorter in omnivorous fish (in crucian carp the body is 2-3 times longer), and in predatory fish it is very short (in pike or pike perch it is only 0.6 - 1.2 body length). The intestine opens with the anus to the outside.

Muscular system fish consists of muscle masses - myomeres, divided connective tissue- myosepta. The number of myomeres corresponds to the number of vertebrae.

All somatic muscles are formed by striated muscle fibers that develop directly from the myotomes of the somites. In fish, these fibers are already differentiated into red and white. Let me remind you that red muscle fibers contain more myoglobin (a respiratory pigment close to hemoglobin, which is also capable of binding molecular oxygen.), but fewer contractile myofibrils, in addition, there are many drops of fat in the sarcoplasm. Therefore, they are capable of long-term operation, but do not exhibit great power. These fibers are located more superficially. White fibers are poorer in myoglobin, but contain much more contractile myofibrils, due to which they are able to contract powerfully, but not as long as red ones. Therefore, when moving slowly at a constant speed, it is mainly the red fibers that contract, while sharp acceleration is provided by the white fibers. Main part muscle fibers white (for example, in asp they make up 96.3%), but in migrating fish the proportion of red fibers is slightly higher.

The state of the muscular system depends on many factors (age, life, size, etc.) For example, in chum salmon (a representative salmon fish) after spawning, muscle tissue loses almost all fat (up to 98.4%) and more than half (57%) of protein.

Some fish have a special device for hunting - an electric organ. It resembles a battery, it consists of special muscle plates separated by gelatinous tissue. The more powerful the organ, the more plates it contains. In sea water, these discharges can spread up to 10 m, and in fresh water only 2 m. There are species that can generate up to 300 V: for example, the electric eel, catfish, and the xiphoid organ of the sawfish.

Respiratory system represented by ectodermal gills. The gill filaments are located directly on the gill arches. Bony fish have an operculum. Fish are able to absorb up to 75% of oxygen dissolved in water. On average, the water of natural reservoirs contains 5-11 ml/l of dissolved oxygen. Gill filaments have complex structure: They contain secondary gill plates that lie perpendicular to the axis of the petal. Skin gas exchange is of great importance in fish, and its relative proportion depends on the conditions in which the fish is located. For example, whitefish that live in well-aerated reservoirs have skin respiration of only 3-9% of the total gas exchange, and fish living in conditions of oxygen deficiency, such as loaches, absorb up to 85% of oxygen through the skin. Such fish can go without water for a long time, maintaining their viability. In labyrinthine fish, as an additional organ of gas exchange, a pocket-like expansion of the gill cavity is formed - a labyrinth. It is abundantly permeated with capillaries in which oxygen is absorbed. The labyrinthine fish include the well-known aquarium fish: macropods, gourami, lalius, and cockerels. Often, fish grab air with their mouths, swallowing it, and in the intestines, oxygen is absorbed by capillaries that weave around the intestines, and up to 50% of the oxygen is absorbed.

However, excess oxygen is also harmful to fish. When water is oversaturated with oxygen, the breathing and coordination of fish movements are disrupted, the gills become covered with bubbles, and the blood becomes foamy. Too much oxygen is also harmful for incubating eggs, with significant death of eggs observed, and many malformed eggs appear among the juveniles. The rate of gas exchange is also influenced by the carbon dioxide content. If there is a lot of it in the water, then the hemoglobin flowing to the gills of venous blood does not lose contact with carbon dioxide and therefore does not bind with oxygen. Established if the carbon dioxide content in the atmospheric air is over 1-5%. then the fish die from asphyxia.

Excretory system represented by ribbon-shaped kidneys located on the sides of the spinal column above the swim bladder. The anterior section of the kidneys is composed of lymphoid tissue and performs the function of a hematopoietic organ; old red blood cells are also retained and killed in it. The kidneys quickly react to the condition of the fish (For example, if there is a lack of oxygen in the water, it decreases in volume). The main end product in bony fish is not urea, but ammonia, which is much more toxic and requires significant dilution. The kidneys excrete up to 300 ml/kg of body weight per day of urine. Freshwater fish can also live in salt water, removing excess salts through urine, feces and partly through the skin.

U sea ​​fish water is lost osmotically, mainly through the gills, and the amount of urine they produce is significantly reduced - 3-23 ml/kg per day. Salts are released through the gills and through mucus secreted by the skin.

Reproductive system

Male reproductive system consists of paired elongated sac-shaped testes, from the walls of which numerous seminiferous tubules extend into the organ, uniting towards the excretory duct. If the tubules twist strongly in different planes, then the testis is classified as cyprinoid type. The excretory duct is located in the upper part of the organ. Percoid testes are characterized by a radial course of the seminiferous tubules, with the excretory duct located in the center of the organ, which has a triangular shape in cross section. Cyprinoid testes are found in sturgeon, carp, catfish, pike, cod, herring, etc., and percoid testes are found in perch, stickleback, etc. The vas deferens of the testes in bony fishes open with a common genital opening behind the anus

Women's reproductive system is represented by paired (in some species, such as perch, the ovary is single) elongated sac-like hollow ovaries, occupying approximately the same position in the body as the testes.

Part of the ovarian membrane extends and forms a duct through which mature eggs (called eggs in fish) exit either into the urogenital sinus or directly out through an independent unpaired genital opening lying behind the anus.

Reproduction.

Life cycle fish are divided into periods that differ in a number of biological, morphological and physiological characteristics .

The following periods are distinguished in the individual development of fish: embryonic, larval, fry, juvenile (immature), adult (sexually mature) organism, senile.

Embryonic period includes two subperiods: 1) actually embryonic, when development is underway in the egg shell. 2) the sub-period of the free embryo, when development continues outside the egg shell, the embryo is fed by the yolk until the juveniles switch to exogenous nutrition.

Larval period begins from the moment of resorption of the yolk and the transition to external nutrition. Larvae differ from adult fish both externally and internally: they have underdeveloped gills, no scales, and undifferentiated fins and other organs.

Juvenile period occurs when the body becomes similar to adult fish, in appearance the fry is similar to an adult fish.

In autumn, fish are called fingerlings - fish of this summer, i.e. they lived for one summer.

Juvenile period lasts until puberty .

The period of an adult organism (Pubertal period) begins from the moment of puberty, when all genital organs are formed and secondary sexual characteristics are expressed, if any. The body is capable of reproducing

Senile period characterized by loss of ability to reproduce

In most bony fishes, fertilization is external, and the process of laying eggs (spawn) is called spawning. In some species it may be accompanied by complex behavior of sexual partners, especially complex rituals are demonstrated different kinds cichlids, and these fish are distinguished by the fact that they choose a partner for themselves (sometimes for life) in accordance with their own views, for example, in an aquarium they cannot be forced to breed offspring with an “unattractive” representative of the opposite sex. Often during spawning, the structure of the fish changes. Unlike cartilaginous fish, many species of bony fish take care of their offspring. This applies to the same cichlids, in which the offspring are protected by both parents. Males of labyrinth fish (for example, gourami) build a floating nest from foam, where they place their eggs (interestingly, after spawning, females are expelled by the male and do not care about the offspring). The male three-spined stickleback builds a nest from blades of grass, then looks after the hatching young for several days. African tilapia takes interesting care of its offspring - the fish hatches eggs in its mouth, but even after the fry hatch, in case of danger, the fry quickly swim into big mouth parents and remain there until the situation becomes calm.

Many species migrate from the sea to rivers to spawn, usually to the place where they themselves were born (such fish are called migratory). They demonstrate amazing navigational abilities when they accurately find the way thousands of kilometers to the desired river, choosing it among many others. It is believed that a subtle sense of smell helps here, since salmon become very excited if water from their native river is added to the surrounding water, but remain unperturbed when water from a “foreign” river is added. European eels, on the contrary, as adults they live in the rivers of Europe, but for spawning they make a long migration to the Sargasso Sea, where they spawn at a depth of about 200 m.

The number of eggs that the female lays varies widely from single to astronomical. For example, a female sunfish lays up to 30 million eggs - a record even among fish. The eggs of some species float freely in the water, others are attached to aquatic plants, the surface of bottom stones and other underwater objects, while the eggs are laid in different types looks different. The eggs are usually small in size, covered thin shell and contain a lot of yolk located near one of the poles (telolecithal eggs). The development of bony fish most often occurs through the larval stage.

Among bony fish there are also viviparous forms. These include, for example, guppies, mollies and some others, well known to aquarists, and the number of babies born can be quite large, for example, an eelpout gives birth to 100 - 300 babies. A significant part of the eggs is eaten by other fish; as a rule, many juveniles die, so only a small part of the offspring survives to adulthood. It was noted that in less fertile fish the relative proportion of surviving juveniles is significantly higher than in more fertile ones.

Commercial and pond fish are usually dioecious. The gonads in females are the ovaries, in which eggs and eggs are formed. Among fishermen, the ovaries are called ovaries. The male gonads are called testes. Most carp, salmon and perch fish reach sexual maturity at 2-4 years. Sterlet matures at 6-10 years, sturgeon at 12-13 years, beluga at 15-18 years. Males mature 1-2 years earlier than females. On the rate of fish maturation big influence temperature and nutrition have an effect.

In ichthyology, the mating act in fish is called spawning. The female spawns eggs into the water, and the male pours sperm on them. The place where this act occurs is called a spawning ground. Our pond fish spawn once a year. External sexual characteristics in fish are usually weakly expressed. However, during the spawning period, male carp, bream, Baikal omul and other fish, a so-called pearl rash appears - pearlescent tubercles resembling warts appear all over the body. In salmonids, the male's lower jaw extends beyond the upper jaw. The upper jaw becomes curved and a hump grows on the back. In some species, sex is poorly determined even during the spawning period. In this case, the abdomen is slightly pressed and individual eggs emerge from the genital opening. The stage of maturity is determined using a specially developed scale. (Table 1)

Table 1 Stages of maturity in sturgeon fish:

Maturity stage	Appearance gonads in sturgeons	Note
Zero (0)	Gender is invisible to the naked eye	Young immature individuals
First (1)	Gender is distinguishable with the naked eye. The ovaries (ovaries) in females are in the form of a pink cord, divided into lobes. The milt (testes) in males are in the form of narrow ribbons, pressed to the spine.	Individuals with gonads in stage 1 have never spawned.
Second (2)	The ovaries are developed, but the eggs are not yet pigmented and are enclosed in fat. The seminal glands are more developed than in the previous stage; they appear as ribbons, although wider than in the first stage, but still relatively thin	This stage may include individuals that have already spawned previously.
Third (3)	The eggs of females are encased in fat. The seminal glands are thick pink cords
Fourth (4)	Caviar is easily separated from the egg and easily passes through the screen (commercial caviar). The seminal glands (milt) are completely white
Fifth (5)	Flowable caviar and milt
Sixth (6)	Sexual products are swept out	After spawning, the gonads from stage 4 pass directly into the second stage

“Reproduction and development of fish” - Make up a logically connected story using terms (work in pairs). Solving biological problems. Ovules. Choose the letter that corresponds to the correct answer and write it in order. Sperm. What new and interesting things did I learn in class today? What was my biggest success in class today?

“Fish biology” - And the second is the artificial reproduction of aquatic biological resources. Aquaculture has two main directions. Main production and technological processes in pond fish farming. Biology and pathology of fish. Purpose of the discipline:

“Fish Class” - Dependence of the appearance of fish on habitat conditions. The meaning of fish. Basic organ systems of fish. Answer the test questions. What group of living organisms are we studying? Habitat. Sense organs. Respiratory system. The fish body is complex. Cartilaginous fish. Internal structure of the body of a fish. Class "Pisces". Bony fish.

“Pisces superclass” - the central nervous system consists of ... the brain and ... the brain. Source of vitamins and minerals D, Na, K, P, Mg, S, Cl, Fe. Artificial reproduction. The nervous system consists of ... parts and ... parts. Continue developing skills in using ICT in biology lessons. " Game fish. Aesthetic value. Regulate the number of aquatic animals.

“Fish Dishes” - Types of fish. Primary processing fish. Why should fish dishes be included in the human diet? What dishes can be prepared from fish? Fish dishes. Fish families. When serving, the fish dish is placed on a plate, with the side dish placed on the side. Good quality of fish. Do you know how you can determine the freshness of fish?

“Fish class 7th grade” - TASK No. 2: Oral work with terms: Check homework. The location of scales on the body of a fish (carp). Examine the fins of the fish. Ribbon-shaped (eel). Variety of fish body shapes. Purpose: to study external structure and modes of movement of fish. Cold-blooded. 7) They reproduce by laying eggs into water; fertilization is external.

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