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Biology Animals 7th grade River perch External and internal structure The presentation was prepared by: teacher of biology and chemistry Merkulova E.V. School No. 26, Ryazan
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Systematic position river perch Type Chordata Subtype Cranial or Vertebrates Superclass Fishes Class Bony fishes Subclass Ray-finned Superorder Teleosts Order Perciformes Family Perciformes Genus Freshwater perch Species River perch
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What characteristics are common to chordates? General signs chordates: the body is bilaterally symmetrical; have an axial skeleton - a chord, a dense supporting cord, in skullless animals it remains throughout life, in vertebrates it is replaced during the process individual development a spine consisting of individual vertebrae; the through intestine is located under the chord; the central nervous system in the form of a neural tube is located above the chord, on the dorsal side of the body; from the anterior section of the digestive tube - the pharynx, the organs of the respiratory system (gills or lungs) develop; the circulatory system is closed; the heart is located on the ventral side of the body, under the digestive canal.
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River perch is a common inhabitant fresh water. In the USSR it is found in rivers and lakes almost everywhere, except Far East. Water exhibits noticeable resistance to bodies moving in it. Perch, like many other fish, has a streamlined shape - this helps it move quickly in the water. The perch's head smoothly transitions into the body, and the body into the tail. At the pointed front end of the head there is a mouth with lips that can open wide. On the top of the head two pairs of small holes are visible - nostrils leading to the olfactory organ. On its sides there are two big eyes. Fins. Bending the laterally flattened body and tail first to the right and then to the left, the perch moves forward. When swimming, fins play an important role. Each fin consists of a thin membrane of skin, which is supported by bony fin rays. When the rays spread out, the skin between them stretches and the surface of the fin increases.
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The perch has two dorsal fins: a large one in front and a smaller one in the back. Number of dorsal fins different types fish may vary. At the end of the tail there is a large two-lobed caudal fin, and on the underside of the tail there is an anal fin. All these fins are unpaired. Fish also have paired fins - there are always two pairs of them. The pectoral paired fins (front pair of limbs) are placed on the sides of the body behind the head of the perch! ventral paired fins (rear pair of limbs) - on the underside of the body. Main role When moving forward, the caudal fin plays. The paired fins are important for turning, stopping, moving forward slowly, and maintaining balance. The dorsal and anal fins give the fish body stability when moving forward and making sharp turns.
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Covers and coloring. The body of the perch is covered with bony scales. Each scale with its front edge is immersed in the skin, and with its rear edge it overlaps the scales of the next row. Together they form a protective cover - scales that do not interfere with body movements. As the fish grows, the scales also increase in size and can be used to determine the age of the fish. The outside of the scales is covered with a layer of mucus, which is secreted by the skin glands. Mucus reduces friction between the fish's body and water and serves as protection against bacteria and mold. Like most fish, the belly of the perch is lighter than that of the epine. From above, the back merges to a certain extent with dark background bottom. From below, the light belly is less noticeable against the light background of the water surface. The body color of a perch depends on environment: In forest lakes with a dark bottom it has a dark color, sometimes even completely black perches are found there. Perches with light and bright colors live in reservoirs with a light sandy bottom. Perch often hides in thickets. Here the greenish color of its sides with vertical dark stripes makes the perch invisible. This protective coloring helps him hide from enemies and better watch over his prey. A narrow dark lateral line runs along the sides of the perch’s body from head to tail.
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The skeleton of a perch consists of a large number of bones. Its basis is the spine, which stretches along the entire body of the fish from the head to the caudal fin. The spine is formed a large number vertebrae (perch has 39-42). Fish and other animals whose skeleton is based on the spine are called vertebrates, and all other animals are called invertebrates. When a perch develops in the egg, a notochord appears in the place of its future spine. Later, vertebrae appear around the notochord. In adult perch, only small cartilaginous remains between the vertebrae are preserved from the notochord. In beluga, sturgeon and some other species of fish, as well as in the lancelet, the notochord is maintained throughout life. Each vertebra consists of a body and a superior arch ending in a long superior process. Together, the upper arches form the spinal canal, in which the spinal cord is located. In the trunk section of the body, the ribs are attached to the vertebrae from the sides. There are no ribs in the caudal region; each vertebra located in it is equipped with a lower arch ending in a long lower process.
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In front, the skeleton of the head, the skull, is firmly articulated with the spine. There is also a skeleton in the fins. In paired pectoral fins, the skeleton of the fins is connected to the spine by bones shoulder girdle. The bones connecting the skeleton of the paired pelvic fins to the spine are not developed in the perch. The skeleton has great importance: It serves as a support for muscles and protection for internal organs. Musculature of fish. Under the skin of fish there are muscles attached to the bones that form the musculature. The strongest of them are located on the dorsal side of the body and in the tail. The contraction and relaxation of muscles causes the fish's body to flex, helping it move through the water. The head and fins contain muscles that move the jaws, gill covers and fins.
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Body cavity. In the body section of the fish, under the spine, there is a large body cavity in which the internal organs are located. Digestive system. Perch is a predator. It feeds on a variety of aquatic animals, including other species of fish. The perch captures and holds its prey sharp teeth sitting on the jaws. After swallowing, food passes through the pharynx and esophagus into the stomach. Perch swallows its prey whole, and due to this, its stomach has the ability to greatly stretch. Microscopic glands in the walls of the stomach secrete gastric juice. Under its influence, food begins to be digested. The partially modified food then passes into the small intestine, where it is acted upon by the digestive juice of the pancreas and bile coming from the liver. The supply of bile accumulates in the gallbladder. Nutrients penetrate through the walls into the blood, and undigested residues enter the hindgut and are thrown out.
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Swim bladder. In perch, like in many other fish, the intestine has a special thin-walled outgrowth filled with a mixture of gases - a swim bladder. In an adult perch, the connection between the bladder and the intestine is lost, but in its larvae and in some other fish (for example, roach or carp), a small tube remains between the intestine and the bladder for the rest of its life. As the fish descends into the depths, the bubble decreases in volume and the density of the fish increases. This promotes rapid immersion. When floating, the volume of the bubble increases and the fish becomes relatively lighter. As long as the fish is at the same depth, the volume of the bubble does not change. This allows the fish to remain motionless, as if hanging in the water column.
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Respiratory system. Fish breathe oxygen dissolved in water. The fish constantly swallows water. From oral cavity water passes through the gill slits, which permeate the walls of the pharynx, and washes the respiratory organs - the gills. In perch, they consist of gill arches, on each of which there are bright red gill filaments on one side and whitish gill rakers on the other. Gill rakers are a filtering apparatus: they prevent prey from slipping out through the gill slits. The gill filaments are penetrated by the smallest blood vessels - capillaries. Through the thin walls of the gill filaments, oxygen dissolved in water penetrates into the blood, and carbon dioxide is removed from the blood into the water. If there is little oxygen, then the fish rise to the surface and begin to take in air with their mouths. Prolonged exposure to water containing little oxygen can cause fish death. In winter, there is sometimes a lack of oxygen under ice in reservoirs. Then the fish die. To prevent freezing, it is useful to make holes in the ice. Dried gill filaments cannot allow oxygen and carbon dioxide to pass through. Therefore, fish taken out of the water quickly die. On the outside, the delicate gills are covered with protective gill covers.
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The circulatory system of fish is closed. It consists of the heart and blood vessels. The vessels leaving the heart are called arteries; vessels that bring blood to the heart are veins. The heart of the fish is two-chambered. It consists of the atrium and ventricle, the muscular walls of which alternately contract. From the atrium, blood is pushed into the ventricle, and from it into a large artery - the abdominal aorta. Valves prevent blood from flowing back. The abdominal aorta goes to the gills, and smaller vessels extend from it to the right and left. The blood flowing in them is dark in color, saturated with carbon dioxide and is called venous. In the gills, the vessels branch into capillaries. The blood flowing in them is freed from carbon dioxide and is saturated with oxygen. In the vessels extending from the gills, scarlet, oxygenated arterial blood flows. It gathers into the dorsal aorta, which runs along the body under the spine. In the caudal region, the dorsal aorta passes through the lower vertebral arches. From the dorsal aorta branch smaller arteries that branch in various organs to capillaries. Through the walls of these capillaries, oxygen and nutrients enter the tissues, and from them carbon dioxide and other waste products enter the blood. Gradually, the scarlet arterial blood darkens and turns into venous blood, containing a lot of carbon dioxide and little oxygen. Venous blood collects in the veins and flows through them into the atrium. Thus, the blood continuously circulates one at a time vicious circle blood circulation
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Excretory system. In the upper part of the body cavity there are two ribbon-shaped red-brown buds. In the capillaries of the kidneys, waste products are filtered from the blood, forming urine. It passes through two ureters to bladder, opening outwards behind the anus. NERVOUS SYSTEM, SENSE ORGANS AND BEHAVIOR OF FISH
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Sense organs allow fish to navigate their environment well. Important role at the same time the eyes play. Perch sees only relatively close range, he distinguishes the shape and color of objects. In front of each eye of the perch there are two openings - nostrils, leading to a blind sac with sensitive cells. This is the organ of smell. The hearing organs are not visible from the outside; they are located on the right and left in the bones of the back of the skull. Due to the density of water sound waves are well transmitted through the bones of the skull and are perceived by the hearing organs of the fish. Experiments have shown that fish can hear the steps of a person walking along the shore, the ringing of a bell, a gunshot. Taste organs - sensitive cells - are located in perch, like in other fish, not only in the oral cavity, but also scattered over the entire surface of the body. There are also tactile cells there. Some fish (for example, catfish, carp, cod) have tactile antennae on their heads.
Fish- a vertebrate animal adapted to live in an aquatic environment. The body of the fish has a streamlined shape. There is no clear boundary between the head, body and tail. The fish whips its tail forcefully from side to side, making wave-like movements. The head is motionlessly articulated with the spine. The basis of the internal skeleton of a fish is the spine and skull.
A - general form: 1 - jaws; 2 - skull; 3 - gill cover; 4 - shoulder girdle; 5 - skeleton of the pectoral fin; 6 - skeleton of the ventral fin; 7 - ribs; 8 - fin rays; 9 - vertebrae;
B - trunk vertebra;
B - caudal vertebra: 1 - spinous process; 2 - upper arc; 3 - lateral process; 4 - lower arc
The spine consists of several dozen vertebrae, similar to each other. Each vertebra has a thickened part - the vertebral body, as well as the upper and lower arches. The superior arches together form the canal in which the spinal cord lies (Fig. B). The arches protect him from injury. Long spinous processes protrude upward from the arches. In the trunk region, the lower arches (lateral processes) are open. The ribs are adjacent to the lateral processes of the vertebrae - they cover the internal organs and serve as a support for the trunk muscles. In the caudal region, the lower arches of the vertebrae form a canal through which blood vessels pass.
A small braincase, or skull, is visible in the skeleton of the head. The bones of the skull protect the brain. The main part of the head skeleton consists of the upper and lower jaws, the bones of the eye sockets and the gill apparatus.
Large gill covers are clearly visible in the gill apparatus. If you lift them, you can see the gill arches - they are paired: left and right. Gills are located on the gill arches. There are few muscles in the head; they are located in the area of the gill covers, jaws and on the back of the head. There are skeletons of unpaired and paired fins. The skeleton of unpaired fins consists of many elongated bones embedded in the thickness of the muscles. Skeleton paired fin
consists of a belt skeleton and a free limb skeleton. The skeleton of the pectoral girdle is attached to the skeleton of the head. The skeleton of the free limb (the fin itself) includes many small and elongated bones. The abdominal girdle is formed by one bone. The skeleton of the free pelvic fin consists of many long bones. Thus, the skeleton provides support for the body and organs of movement, protects the most important organs
. The main muscles are located evenly in the dorsal part of the fish's body; The muscles that move the tail are especially well developed.
In fish, paired and unpaired fins are distinguished: unpaired - dorsal, anal and caudal fins; paired fins include pectoral and ventral fins. The pectoral fins correspond to the forelimbs of terrestrial animals, and the ventral fins correspond to hind limbs. Fins are formations consisting of hard and soft rays, connected by a membrane or free. The number of fins, structure and location of different types of fish are different. In some species, the fins are fused and form the so-called fin border. Support system creates an internal skeleton - a spinal column, consisting of biconcave vertebrae with paired spinous processes, which serve as a support for the dorsal and abdominal swimming muscles. The fins have interneural ossicles that support fin rays for support. Muscle segments E-shape, each of them has a shell. The outer surface of the muscles is covered with skin, which is covered, as a rule, with a flexible shell formed by bone plates - scales. Thus, fish, in a sense, have exoskeleton. Numerous glands secrete mucus, which makes the surface of the fish slippery. Thanks to the mucus layer, the fish experiences less water resistance and is also protected from fungi and bacteria. On the sides of the fish, rows of scales of different shapes are visible. This is the side line. The lateral line may be intermittent, continuous, or completely absent. It is located on both sides of the body from the gill cover to the caudal fin.
The two-chambered heart of the fish is located in the front of the body. The circulatory system is the simplest: the heart pumps blood into the gills; enriched with oxygen, it enters various organs of the body, and then again to the heart, gills, etc.
The mouth of many fish species is equipped with teeth; teeth are found not only on the jaws, but often also on the palatine bones, vomer, and tongue. Teeth are frequently renewed. U predatory fish they are usually cone-shaped and very sharp. The pharynx, short esophagus and stomach are elastic. In the back of the stomach there may be different quantity blind outgrowths. The intestine is poorly differentiated into sections, ending with the anus located in front of the anal fin. Fatty deposits often form around the intestines on the mesenteries. The internal organs of fish also include the liver, gallbladder, pancreas and spleen.
The kidneys are located under the spine, along it. When gutting fish, the kidneys can easily be mistaken for dried blood. The bladder is located near the anus.
The reproductive organs - the ovaries in females and the testes in males - have excretory canals into the genital opening. Of the internal organs, except for the gonads, only the kidneys are paired.
Internal structure of bony fish (female perch): 1 - mouth; 2 - gills; 3 - heart; 4 - liver; - gallbladder; 6 - stomach; 7 - swim bladder; 8 - intestines; 9 - brain; 10 - spine; 11 - spinal cord; 12 - muscles; 13 - kidney; 14 - spleen; 15 - ovary; 16 - anus; 17 - genital opening; 18 - urinary opening; 19 - bladder
In the body cavity under the kidneys there is a swim bladder - a hydrostatic apparatus for swimming fish at different depths. In some species of fish, the swim bladder and the pharynx cavity communicate through a special duct, but in perch, for example, there is no such duct. The swim bladder is filled with gas, which includes nitrogen, oxygen, and carbon dioxide. Their ratio is regulated by the system of blood vessels in the bladder walls. Fish with a swim bladder open type, can change depth faster than fish with a closed swim bladder, since excess gas escapes through the duct between the swim bladder and the pharyngeal cavity. If a fish with a closed swim bladder is pulled out of the water too quickly great depth, it will swell and squeeze the stomach out through the mouth.
In carp fish, the swim bladder consists of two parts and is always inflated. When a fish dies, the swim bladder muscles relax and the fish floats to the surface of the water. The bladder allows the fish to easily swim in the water with little muscle energy consumption.
All fins have a special effect on the movement of the fish. The dorsal and anal fins act as stabilizers. Other fins, in addition to the caudal one, serve to adjust the position of the body. Sometimes fish use their pectoral fins for slow movement. The metabolism of the fish is slowed down by the lady, in cold water. In it, the fish tire faster than in warm water.
Circulatory system closed fish (Fig. A). Blood continuously flows through the vessels due to the contraction of the two-chambered heart, consisting of an atrium and a ventricle. Passes through the heart deoxygenated blood containing carbon dioxide. When the ventricle contracts, it directs blood forward into a large vessel - the abdominal aorta. In the region of the gills, it splits into four pairs of afferent gill arteries. They branch capillaries forward in the gill filaments. Here the blood is freed from carbon dioxide, enriched with oxygen (becomes arterial) and is sent through the efferent branchial arteries to the dorsal aorta. This second large vessel carries arterial blood to all organs of the body and to the head. In organs and tissues, the blood releases oxygen, is saturated with carbon dioxide (becomes venous) and enters the heart through the veins.
: A - diagram circulatory system: 1 - heart; 2 - abdominal aorta; 3 - afferent gill arteries: 4 - efferent gill arteries; 5 - carotid artery (carries blood to the head); 6 - dorsal aorta; 7 - cardinal veins (carry blood to the heart); 8 - abdominal vein; 9 - capillary network of internal organs: B - gill arch: 1 - gill rakers; 2 - gill filaments; 3 - gill plate; B - breathing pattern: 1 - direction of water flow; 2 - gills; 3 - gill covers
Respiratory system located in the pharynx (Fig. B, C). The skeletal support of the gill apparatus is provided by four pairs of vertical gill arches, to which the gill plates are attached. They are divided into fringed gill filaments. Inside them are thin-walled blood vessels branching into capillaries. Gas exchange occurs through the walls of capillaries: absorption of oxygen from water and release of carbon dioxide. Water moves between the gill filaments due to the contraction of the pharyngeal muscles and the movement of the gill covers. On the side of the pharynx, bony gill arches bear gill rakers. They protect the soft, delicate gills from becoming clogged with food particles.
Class Bony fish.
river perch.
Like cartilaginous fish The bony body is divided into three sections. The boundary between the head and the body is the gill slit, and between the body and the tail is the anus. There are at least 12 different morphological types of fish appearance: torpedo-shaped (tuna, herring, cod), serpentine (eels), ribbon-shaped (saberfish), flattened (bream, flounder).
There are eyes on the sides of the head. In front of them are the olfactory openings - the nostrils. The squirter is preserved only in sturgeons. The gill arches are located in the gill cavity and are covered by bony gill covers. Paired fins include pectoral and ventral. TO unpaired fins include dorsal, anal and caudal. In front of the anal fin there are three openings: anal, genital and excretory.
Veils.
The multilayered epidermis contains numerous unicellular glands. The mucus secreted by these glands performs numerous functions: it has bactericidal properties, participates in the release of metabolic products and water-salt metabolism, accelerates blood clotting and reduces the friction of fish on water, and secretes a secretion when the skin is damaged (ichthyopterin), which is also called the “substance of fear” , it serves as a signal of danger and releases pheromones.
In the lower layers of the epidermis there are pigment cells - chromatophores.
Below the epidermis is the dermis.
The scales of bony fishes are represented by bony scales that form in the corium. The most primitive is ganoid scale(armored pike and polyfins), cosmoid (in lobefins and lungfishes), in most bony fishes the scales are elasmoid, formed only by bony plates. Depending on the condition of the outer edge, cycloid and ctenoid scales are distinguished. Each scale lies in a special pocket. The scales overlap each other in the form of tiles. Light (wide) and dark (narrow) growth rings are visible on the scales. The light wide layer is the summer growth of scales, the dark narrow layer is winter growth. They can be used to determine the age of the fish.
Skeleton.
It is formed by bones; only sturgeons retain a significant amount of cartilaginous elements throughout their lives.
1. Axial skeleton includes the spinal column and skull. Unlike cartilaginous fish, whose ribs limit the body cavity only from above, bony fish have long ribs and also limit the body cavity from the sides. The last caudal vertebra has the attachment surface for the supporting structures of the caudal fin. Each type of fish is characterized by a certain total vertebrae The visceral also includes the bones of the gill cover.
2. Additional.
The belt of the forelimbs—the pectoral fins—is formed by a small scapula and coracoid. The pectoral fins lack basalia, so the bony radials are attached directly to the bones of the girdle. The skeleton of the fins themselves is formed by bony rays of cutaneous origin, which are attached to the radials.
The belt of the hind limbs consists of two fused bones, freely lying in the thickness of the muscles, to which the bony rays of the ventral fins are attached.
Muscular system.
Better developed than cartilaginous ones. It is represented by the muscles of the trunk, head and fins.
Clusters of specialized muscle fibers form electrical organs of fish, which can be located in different parts bodies. The electrical organ resembles a battery; it consists of special muscle plates separated by gelatinous tissue. The more powerful the electric organ, the more plates it contains.
Digestive system.
The oral cavity is equipped with numerous teeth. Typically, teeth are fused to the surface of the bone. The basis of the tooth is dentin, covered on the outside with a thin layer of enamel. In fish feeding plant foods or plankton teeth are missing. The pharynx, penetrated by gill slits, is actively involved in the digestion process. The entry of food into the oral cavity 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 do not allow it to pass through. In fish that feed on plankton, the stamens form a powerful filtering apparatus; in predators they are short. Esophagus. Stomach. The small intestine, where the ducts of the liver and pancreas flow. The small intestine of bony fishes is much longer and forms loops. This is where the main breakdown and absorption occurs. The large intestine opens into the anus. The anatomically formed pancreas is absent, its structures are dissociated in the liver tissue.
Most have a swim bladder, which embryonically develops as an outgrowth of the esophagus. Depending on whether the connection between the bladder and the esophagus is maintained, fish can be open-vesical or closed-vesical. The swim bladder is filled with air, which significantly reduces specific gravity fish and allows it to hang 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 bladders have a special network of blood capillaries in the wall of the bladder.
Respiratory system.
Each gill of bony fish consists of a gill arch on which gill filaments sit in two rows. Gill rakers extend from the inner walls of the gill arches.
The respiratory act of bony fishes includes two stages. In the first of them, the fish lifts its gill covers and fresh water enters through the mouth opening. At the second stage, the retracted gill covers are pressed against the body with force and water exits into the environment through the gills. At high swimming speeds, the bony ones switch to the shark type of breathing.
Circulatory system.
Features: 4 gill vessels;
Excretory system.
Mesanephros. The main end product of nitrogen metabolism is ammonia.
Nervous system.
The brain is more primitive.
A taste organ has appeared - small taste buds that are scattered over the entire outer surface of the skin.
Reproductive system.
Male reproductive system - paired elongated sac-shaped testes, vas deferens, genital opening.
The female reproductive system is paired ovaries. Part of the membrane is elongated and forms a duct, which opens into the genital opening.
Fertilization is external. The process of laying eggs is called spawning. Development is direct or with the larval stage.
1. Features of the external structure of bony fish using the example of river perch.
Fish are ancient proto-aquatic vertebrates. Unlike skullless ones, they lead an active lifestyle. The features of their structure are associated with aquatic environment. More than 20 thousand species of fish are known, which are grouped into two classes: Cartilaginous and Bony. The most numerous and diverse bony fish, more than 90% of which are a group of bony fish. These include herring, cod, carp, salmon, perch, pike, etc.
A typical representative is river perch. The body shape is streamlined, the head smoothly merges into the body, and the body into the tail. On the head there is a mouth with lips, large eyes, nostrils and gill covers. There are fins: paired (pectoral and abdominal) and unpaired - caudal, dorsal and anal. The skin is covered with bone scales. The scales overlap each other in a tiled manner. The skin glands secrete mucus that covers the scales and reduces friction of the body with water.
2. Features of the internal structure of bony fish using the example of river perch.Material from the site
The skeleton of a river perch consists of large number bones. It contains the skull, spine, skeleton of the shoulder and pelvic girdles, and the skeleton of the fins. The skull consists of the braincase, jaw bones, gill arches and gill covers. The spine consists of the trunk and caudal vertebrae. The ribs are attached to the trunk vertebrae. The digestive system includes the mouth with teeth, pharynx, esophagus, stomach, small intestine, where the ducts of the gallbladder, liver and pancreas open, the hind intestine, and the anus. There is a swim bladder (an outgrowth of the anterior section of the intestine) filled with a mixture of gases. It participates in gas exchange and is a hydrostatic organ. Fish breathe through gills, which consist of gill arches and gill filaments, pierced blood vessels. Perch has four pairs of them. The circulatory system is characterized by a two-chambered heart and one circulation. Venous blood flows through the heart, which becomes arterial in the gills. The excretory system includes long trunk kidneys, ureters and bladder. Nervous system consists of the brain and spinal cord and the nerves extending from them. The brain is protected by the bones of the cranium and consists of five sections: the medulla oblongata, cerebellum, midbrain, intermediate section and small forebrain hemispheres with olfactory lobes. The organs of vision are the eyes, which have a flat cornea and a large lens. Eyelids are missing. The organs of smell are in the nasal cavity, the organ of hearing is the inner ear, the organ of taste is in the mouth and lips. A clearly visible lateral line stretches along the body - an organ that perceives the direction and force of water flow, as well as sound vibrations. Touch cells are scattered throughout the body. Bony fish are dioecious animals. Reproductive organs: paired testes and ovaries, reproductive ducts. Fertilization is external. Development occurs with transformation (larva - fry - adult fish).
Fish - aquatic animals, adapted to life in fresh water bodies and sea water. They have a hard skeleton (bone, cartilaginous or partially ossified).
Let's consider the structural features and vital functions of fish using the example of river perch.
Habitat and external structure of fish using the example of river perch
River perch lives in freshwater bodies of water (slow-flowing rivers and lakes) in Europe, Siberia and Central Asia. Water exhibits noticeable resistance to bodies moving in it. Perch, like many other fish, has a streamlined shape - this helps it move quickly in the water. The perch's head smoothly transitions into the body, and the body into the tail. At the pointed front end of the head there is a mouth with lips that can open wide.
Figure: external structure of river perch
On the top of the head two pairs of small holes are visible - nostrils leading to the olfactory organ. On its sides there are two large eyes.
Perch fins
Bending the laterally flattened body and tail first to the right and then to the left, the perch moves forward. When swimming, fins play an important role. Each fin consists of a thin membrane of skin, which is supported by bony fin rays. When the rays spread out, the skin between them stretches and the surface of the fin increases. On the back of the perch there are two fin pins: front big And the rear one is smaller. The number of dorsal fins may vary between different fish species. At the end of the tail there is a large two-lobed caudal fin, on the underside of the tail - anal. All these fins are unpaired. Fish also have paired fins - there are always two pairs of them. Pectoral fins(front pair of limbs) are placed on the sides of the perch's body behind the head, paired ventral fins (back pair of limbs) are on the underside of the body. The main role in moving forward is played by caudal fin. The paired fins are important for turning, stopping, moving forward slowly, and maintaining balance.
The dorsal and anal fins give the fish body stability when moving forward and making sharp turns.
Cover and color of perch
The body of the perch is covered bone scales. Each scale with its front edge is immersed in the skin, and with its rear edge it overlaps the scales of the next row. Together they form a protective cover - scales that does not interfere with body movements. As the fish grows, the scales also increase in size and can be used to determine the age of the fish.
The outside of the scales is covered with a layer of mucus, which is secreted by the skin glands. Mucus reduces friction between the fish's body and water and serves as protection against bacteria and mold.
Like most fish, the belly of the perch is lighter than the back. From above, the back merges to a certain extent with the dark background of the bottom. From below, the light belly is less noticeable against the light background of the water surface.
The body color of a perch depends on the environment. In forest lakes with a dark bottom it has a dark color, sometimes even completely black perches are found there. Perches with light and bright colors live in reservoirs with a light sandy bottom. Perch often hides in thickets. Here the greenish color of its sides with vertical dark stripes makes the perch invisible. This protective coloring helps him hide from enemies and better watch over his prey.
Along the sides of the perch's body from head to tail runs a narrow dark lateral line. This is a kind of sensory organ.
The skeleton of a perch consists of a large number of bones. Its basis is the spine, which stretches along the entire body of the fish from the head to the caudal fin. The spine is formed by a large number of vertebrae (perch has 39-42).
Figure: Skeleton of a river perch
When a perch develops in the egg, a notochord appears in the place of its future spine. Later, vertebrae appear around the notochord. In adult perch, only small cartilaginous remains between the vertebrae are preserved from the notochord.
Each vertebra consists of body And upper arch, ending in a long upper process. Taken together, the upper arches together with the vertebral bodies form the spinal canal, which contains spinal cord.
In the trunk section of the body, they are attached to the vertebrae at the sides ribs. There are no ribs in the caudal region; each vertebra located in it is equipped with a lower arch ending in a long lower process.
In front, the skeleton of the head is firmly articulated with the spine - scull. There is also a skeleton in the fins.
In paired pectoral fins, the skeleton of the fins is connected to the spine by bones shoulder girdle. The bones connecting the skeleton of the paired pelvic fins to the spine are not developed in the perch.
The skeleton is of great importance: it serves as a support for muscles and protection for internal organs.
River perch muscles
Under the skin there are muscles attached to the bones that form muscles. The strongest of them are located on the dorsal side of the body and in the tail.
The contraction and relaxation of muscles causes the fish's body to bend, allowing it to move in the water. The head and fins contain muscles that move the jaws, gill covers and fins.
Swim bladder of river perch
River perch, like any fish, is heavier than water. Its buoyancy ensures swim bladder. He is in abdominal cavity on top of the intestines it has the shape of a translucent sac filled with gas.
Figure: Internal structure of river perch. Digestive and excretory systems
The swim bladder is formed in the perch embryo as an outgrowth of the intestine on the dorsal side. It loses connection with the gut during the larval stage. The larva should float to the surface of the water 2-3 days after hatching and swallow a little atmospheric air to fill the swim bladder. If this does not happen, the larva cannot swim and dies.
By regulating the volume of the swim bladder, the perch stays at a certain depth, floats up or sinks. When the bladder contracts, excess gas is absorbed by the blood in the capillaries inner surface bubble If the bubble expands, gas enters it from the blood. When the perch sinks into the depths, the bubble decreases in volume - and the density of the fish increases. This promotes rapid immersion. When floating, the volume of the bubble increases and the fish becomes relatively lighter. At the same depth, the volume of the fish's bladder does not change. This allows the fish to remain motionless, as if hanging in the water column.
Unlike river perch, in other fish, such as carp, bream, roach, herring, the swim bladder remains connected to the intestine using an air duct - a thin tube throughout life. Excess gas exits through this duct into the intestines, and from there through the mouth and gill slits into the water.
The main function of the swim bladder is to provide buoyancy for fish. In addition, it helps fish hear better, since, being a good resonator, it amplifies sounds.
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