The internal structure of a fish is the digestive system. External and internal structure of fish

Characteristic features of chordates:

• three-layer structure;
• secondary body cavity;
• the appearance of a chord;
• conquest of all habitats (water, land and air).

During evolution, organs improved:

• movements;
• reproduction;
• breathing;
• blood circulation;
• digestion;
• feelings;
• nervous (regulating and controlling the work of all organs);
• body coverings changed.

Biological meaning of all living things:

They live in freshwater bodies of water; in sea water.

Life expectancy ranges from several months to 100 years.

Dimensions - from 10 mm to 9 meters. (Fish grow all their lives!).

Weight - from a few grams to 2 tons.

Fish are the most ancient proto-aquatic vertebrates. They are able to live only in water; most species are good swimmers. The class of fish in the process of evolution was formed in aquatic environment, the characteristic structural features of these animals are associated with it. The main type of translational movement is lateral wave-like movements due to contractions of the muscles of the tail or the whole body. The pectoral and pelvic paired fins serve as stabilizers, used to raise and lower the body, turn stops, slow smooth movement, and maintain balance. The unpaired dorsal and caudal fins act as a keel, giving stability to the fish's body. The mucous layer on the surface of the skin reduces friction and promotes rapid movement, and also protects the body from pathogens of bacterial and fungal diseases.

External structure of fish

Side line

The lateral line organs are well developed. The lateral line perceives the direction and strength of water flow.

Thanks to this, even when blinded, it does not bump into obstacles and is able to catch moving prey.

Internal structure

Skeleton

The skeleton is the support for well-developed striated muscles. Some muscle segments were partially rebuilt, forming muscle groups in the head, jaws, gill covers, pectoral fins, etc. (ocular, epibranchial and hypobranchial muscles, muscles of paired fins).

swim bladder

Above the intestines there is a thin-walled sac - a swim bladder, filled with a mixture of oxygen, nitrogen and carbon dioxide. The bladder formed from an outgrowth of the intestine. The main function of the swim bladder is hydrostatic. By changing the pressure of gases in the swim bladder, the fish can change the depth of its dive.

If the volume of the swim bladder does not change, the fish is at the same depth, as if hanging in the water column. When the volume of the bubble increases, the fish rises. When lowering, the reverse process occurs. The swim bladder of some fish can participate in gas exchange (as an additional respiratory organ) and serve as a resonator during reproduction. different sounds etc.

Body cavity

Organ system

Digestive

The digestive system begins with the mouth. Perch and other predatory bony fish have numerous small, sharp teeth on their jaws and many bones in their mouths that help them capture and hold prey. There is no muscular tongue. Through the pharynx into the esophagus, food enters the large stomach, where it begins to be digested under the influence of hydrochloric acid and pepsin. Partially digested food enters the small intestine, where the ducts of the pancreas and liver empty. The latter secretes bile, which accumulates in the gallbladder.

At the beginning of the small intestine, blind processes flow into it, due to which the glandular and absorptive surface of the intestine increases. Undigested residues are excreted into the hindgut and removed through the anus.

Respiratory

The respiratory organs—gills—are located on four gill arches in the form of a row of bright red gill filaments, covered on the outside with numerous thin folds that increase the relative surface of the gills.

Water enters the fish's mouth, is filtered through the gill slits, washes the gills, and is thrown out from under the gill cover. Gas exchange occurs in numerous gill capillaries, in which blood flows towards the water washing the gills. Fish are able to absorb 46-82% of oxygen dissolved in water.

Opposite each row of gill filaments are whitish gill rakers with great value for feeding fish: in some they form a filtering apparatus with an appropriate structure, in others they help retain prey in the oral cavity.

Blood

The circulatory system consists of a two-chambered heart and blood vessels. The heart has an atrium and a ventricle.

excretory

The excretory system is represented by two dark red ribbon-like buds, lying below the spinal column almost along the entire body cavity.

The kidneys filter waste products from the blood in the form of urine, which passes through two ureters into the bladder, which opens outward behind the anus. A significant part of the toxic decomposition products (ammonia, urea, etc.) are excreted from the body through the gill filaments of fish.

Nervous

Nervous system has the appearance of a hollow tube thickened in front. Its anterior end forms the brain, which has five sections: anterior, intermediate, midbrain, cerebellum and medulla oblongata.

The centers of different sense organs are located in different parts of the brain. The cavity inside the spinal cord is called the spinal canal.

Sense organs

Taste buds, or taste buds, are located in the mucous membrane of the oral cavity, on the head, antennae, elongated fin rays, and scattered over the entire surface of the body. Tactile corpuscles and thermoreceptors are scattered in the superficial layers of the skin. Receptors of electromagnetic sense are concentrated mainly on the head of fish.

Two big eyes are located on the sides of the head. The lens is round, does not change shape and almost touches the flattened cornea (therefore fish are myopic and see no further than 10-15 meters). In most bony fishes, the retina contains rods and cones. This allows them to adapt to changing light conditions. Most bony fish have color vision.

The hearing organs are represented only by the inner ear, or membranous labyrinth, located on the right and left in the bones of the back of the skull. Sound orientation is very important for aquatic animals. The speed of sound propagation in water is almost 4 times greater than in air (and is close to the sound permeability of fish body tissues). Therefore, even a relatively simple organ of hearing allows fish to perceive sound waves. The hearing organs are anatomically connected to the balance organs.

From the head to the caudal fin, a series of holes stretches along the body—the lateral line. The holes are connected to a channel immersed in the skin, which branches strongly on the head and forms a complex network. The lateral line is a characteristic sensory organ: thanks to it, fish perceive water vibrations, the direction and strength of the current, and waves that are reflected from various objects. With the help of this organ, fish orient themselves in water flows, perceive the direction of movement of prey or predators, and do not bump into hard objects in barely clear water.

Reproduction

Fish breed in water. Most species lay eggs, fertilization is external, sometimes internal, and in these cases viviparity is observed. The development of fertilized eggs lasts from several hours to several months. The larvae that emerge from the eggs have a remnant of the yolk sac with a supply of nutrients. At first they are inactive and feed only on these substances, and then they begin to actively feed on various microscopic aquatic organisms. After a few weeks, the larva develops into a small fish covered with scales and resembling an adult fish.

Fish spawning occurs in different times year. Most freshwater fish lay their eggs among aquatic plants in shallow water. The fertility of fish, on average, is much higher than the fertility of terrestrial vertebrates; this is associated with a large loss of eggs and fry.

Anatomy of fish: structure, shape, color

Digestive system in bony fishes the structure is a little more complicated than in cartilaginous fishes. This is primarily due to differences in the diet of some and others. The digestive system of fish is divided into three parts: the front (mouth, pharynx and esophagus), the middle (stomach, small intestine, liver and pancreas, digestive glands) and hind (large intestine).

Found in fish three types of oral cavity:

— grasping- when predatory fish there are jaws with sharp teeth;

— suction- when the mouth looks like a suction tube (bream);

— crushing- when the jaws are dotted with large but blunt teeth (catfish).

In some planktivorous fish species (herring, silver carp, etc.), the gill apparatus is also involved in the digestive process, holding small animals and sending them to the stomach. Stomach All fish except cyprinids have it. Intestines May be different lengths, depending on the nature of the fish’s diet. In herbivores it is longer, in predators it is shorter.

In the intestines of some fish species there are pyloric appendages- special outgrowths that increase the absorption capacity of the intestine and allow absorption maximum quantity nutrients from food. Fish do not have salivary glands. Food is digested using enzymes, which are secreted by the pancreas, liver and intestinal glands.

Additional materials on the topic: Digestive system of fish.

The digestive system of fish is relatively simple, but in many cases unique.

It varies depending on different types fish, including depending on the type of food.

The structure of the digestive system

The general “framework” of the fish digestive system is as follows:

• Oral cavity;
• Pharynx;
• Esophagus;
• Stomach;
• Intestines. The intestine consists of the rectum, colon, small intestine and anus.

There are fish that also have a cloaca - a hollow organ in which the rectum and ducts of the reproductive and urinary systems are located; this organ is characteristic of cartilaginous and lungfishes.

Not all fish have a stomach. For example, many cyprinids do not have it. Their food is digested in the intestines themselves. Predators most often have a developed stomach.

He may have different structure: in the form of a tube, an oval cavity and even in the form Latin letter V. Substances that break down food in the stomach are pepsin and hydrochloric acid.

Oral cavity

The oral cavity of fish does not have salivary glands. Cyclostomes (lampreys, hagfish), which are sometimes classified as “primitive fish,” have these glands, but they are vital for them: these organisms stick to the victim, pierce its skin with a sharp tongue and inject saliva inside, which dissolves the proteins; In this way, external digestion of food is carried out, which is then absorbed by the animal in liquid form.

However, real fish have taste buds and, therefore, are able to distinguish food by taste. Most predators have teeth, as well as those herbivores that have to grind hard parts of plant food.

fish structure photo

Teeth can often be arranged in several rows and be present not only on the gums, but also in other places in the mouth and on the tongue. Fish teeth are nothing more than modified placoid scales; They do not have roots, but they are constantly renewed - new ones grow in place of those that fall out.

By the way, real language in fish it is also absent; its role is played by the copula (part of the hyoid arch). It does not have its own muscles, unlike the tongue of other groups of animals. Fish that feed on benthos (small bottom-dwelling animals) often have a tubular mouth designed for suction.

Pharynx

The pharynx of fish is often also studded with teeth, the number and structure of which are different. Pharyngeal teeth are necessary for holding and grinding swallowed food; in cyprinids, the same function is performed by the horny organ on the upper part of the pharynx - the philtrum.

Digestive system of fish

Has a pharynx and gill rakers; at predatory species they are short and few in number, while in planktivores the stamens are long and numerous, designed to filter ingested food. The pharynx and oral cavity of fish have glands, but they do not produce saliva as such, but simply mucus, which makes it easier to swallow prey.

After the pharynx comes the esophagus, which is small in most fish. In some fish, such as pufferfish, the esophagus also acts as an air sac and is adapted to inflate the body.

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Digestive system of fish

The digestive system of fish is presented digestive tract and digestive glands.

The digestive tract includes:

1) oral cavity;

2) pharynx;

3) esophagus;

4) stomach;

5) intestines.

Depending on the feeding habits of the fish, these sections vary significantly. Cyclostomes have a sucking type mouthpart; it begins with a suction funnel, at the bottom of which there is a mouth opening. On the inner surface of the funnel there are horny teeth. In the depths of the funnel there is a powerful tongue with teeth. Using a funnel, cyclostomes attach themselves to the victim and drill into its body with their tongue. There are paired areas near the tongue salivary glands, which release substances into the wound that prevent blood clotting and dissolve proteins. Thus, partially digested food enters the oral cavity.

Predatory fish have a large, grasping mouth armed with teeth. Many benthivorous fish have a tube-shaped suction mouth (cyprinid, pipefish); planktivorous - large or medium-sized mouth with or without small teeth (whitefish, herring, etc.); periphytonivores - a mouth in the form of a transverse slit located on the underside of the head, the lower lip is covered with a horny sheath (podust, khramulya).

Most fish in the mouth cavity on the jaws have teeth, which are modified placoid scales. Tooth includes:

1) vitrodentin (outer enamel-like layer);

2) dentin (lime-impregnated organic matter);

3) pulp (a cavity filled with connective tissue with nerves and blood vessels).

Teeth, as a rule, do not have roots and are replaced with new ones as they wear out. In whole-headed and lungfishes, teeth grow continuously; many peaceful species there are no teeth in the oral cavity (cyprinids).

Teeth can be located not only on the jaws, but also on other bones of the oral cavity and even on the tongue. Predatory fish have sharp, recurved teeth that are used to grasp and hold prey. Many stingrays have flat teeth. In catfish, the front teeth are conical and are designed for grasping prey, and the lateral and rear teeth are flattened for crushing shells of mollusks, etc.

Fish do not have a real tongue, which has its own muscles. Its role is played by the unpaired element of the hyoid arch (copula).

The oral cavity of fish passes into the pharynx, the walls of which are pierced by gill slits with gill arches that open outward. On the inside of the gill arches there are gill rakers, the structure of which depends on the feeding pattern of the fish. In predatory fish, gill rakers are few in number, short and are designed to protect the gill filaments and retain prey; in planktivores - numerous, long, used for straining food organisms. The number of gill rakers on the first gill arch is a systematic feature for some species (coregonids).

In some fish, a special epibranchial organ develops in the dorsal wall of the pharynx, which serves to concentrate small food (silver carp).

Predatory fish have:

1) upper pharyngeal teeth (on the upper elements of the gill arches);

2) lower pharyngeal teeth (on the fifth underdeveloped gill arch).

The pharyngeal teeth look like platforms covered with small teeth and serve to hold prey.

Cyprinid fish have highly developed lower pharyngeal teeth, which are located on the fifth underdeveloped gill arch. On the upper wall of the throat of cyprinids there is a hard horny formation - a millstone, which is involved in grinding food. The pharyngeal teeth can be single-row (bream, roach), double-row (bream, shemaya), three-row (carp, barbel). Pharyngeal teeth are replaced annually.

In the oral and pharyngeal cavities of fish there are glands, the mucus of which does not contain digestive enzymes, but facilitates the swallowing of food.

The pharynx passes into a short esophagus. In representatives of the pufferfish order, the esophagus forms an air sac, which serves to inflate the body.

In most fish, the esophagus goes into the stomach. The structure and size of the stomach are related to the nature of nutrition. Thus, pike has a stomach in the form of a tube, perch has a blind outgrowth, some fish have a curved stomach in the shape of the letter V (sharks, rays, salmon, etc.), which consists of two sections:

1) cardiac (anterior);

2) pyloric (posterior).

In cyclostomes, the esophagus passes into the intestine. Some fish do not have a stomach (carp, lungfish, whole-headed, sea ​​cocks, many gobies, monkfish).

Digestive system of fish.

Food from their esophagus enters the intestine, which is divided into three sections: anterior, middle and posterior. The ducts of the liver and pancreas empty into the anterior part of the intestine.

To increase the absorption surface, the fish intestine has a number of features:

1) folded inner surface;

2) spiral valve - an outgrowth of the intestinal wall (in cyclostomes, cartilaginous fish, cartilaginous and bony ganoids, lungfishes, lobe-finned fishes, salmonids);

3) pyloric appendages (herring, salmon, mackerel, mullet); appendages extend from the anterior intestine, gerbils have one appendage, river perch have three, mackerel have about 200; in sturgeons, the pyloric appendages have fused and formed the pyloric gland, which opens into the intestine; the number of pyloric appendages in some species is a systematic feature (salmon, mullet);

4) increase in intestinal length; length is related to the calorie content of food; Predatory fish have a short intestine; silver carp, which feeds on phytoplankton, have an intestinal length 16 times longer than the body.

The intestine ends with the anus, which is usually located in the back of the body in front of the genital and urinary openings. In cartilaginous and lungfishes, the cloaca is preserved.

Digestive glands. The ducts of two digestive glands flow into the anterior intestine: the liver and pancreas.

Cartilaginous fish have a large three-lobed liver (10-20% of body weight). In bony fish, the liver may consist of one, two or three lobes. The liver produces bile, which emulsifies fats and enhances intestinal motility. Detoxification also occurs in the liver toxic substances, coming from the intestines, proteins and carbohydrates are synthesized, glycogen, fat, and vitamins (sharks, cod) accumulate.

Cartilaginous and large sturgeon fish have a separate pancreas. In many fish, pancreatic tissue is located in the liver and is called hepatopancreas (cyprinid); in some fish it is located near the gallbladder and its ducts, the spleen, and in the intestinal mesentery. The pancreas secretes enzymes into the intestines that digest fats, proteins and carbohydrates. Islet cells (endocrine) produce the hormone insulin, which regulates blood sugar levels.

It is believed that the pyloric appendages, along with increasing the absorption surface, have an enzymatic function. In addition to their own digestive enzymes, herbivorous fish species participate in digestion by enzymes secreted by microorganisms that constantly live in the intestines (symbiotic digestion).

Fish is 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 view: 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 ventral fin consists of many long bones.

Thus, the skeleton provides support for the body and organs of movement and 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 the front of the head, above the upper jaw, there are paired nostrils. The fish's eyes are quite large, mobile, they have no eyelids, and are constantly open. On the sides of the head there are gill covers that cover the cavities with gills. Through the mouth, water enters the pharynx, is filtered through the gill filaments and is pushed out through the gill openings. The exchange of gases is carried out using the capillaries of the gill filaments.

In fish, there are paired and unpaired fins: unpaired - dorsal, anal and caudal fins; paired fins include pectoral and ventral fins. The pectoral fins correspond to the forelimbs of land animals, and the ventral fins correspond to the 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. Creates a support system internal skeleton- the spinal column, consisting of biconcave vertebrae with paired spinous processes, which serve as support for the dorsal and abdominal swimming muscles. The fins have interneural ossicles that support fin rays for support. The muscle segments are E-shaped, each of them has a sheath. 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 an 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. In 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, gall bladder, 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 - ovaries in females and testes in males - have excretory canals in genital opening. Of the internal organs, except for the gonads, only the kidneys are paired.

Internal structure bonefish (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, carbon dioxide. Their ratio is regulated by the system of blood vessels in the walls of the bladder. 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 from great depths, 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 pectoral fins the fish uses it to move slowly. The metabolism of the fish is slowed down by the lady, in cold water. In it, the fish tire faster than in warm water.

The circulatory system of fish is closed (Fig. A). Blood continuously flows through the vessels due to the contraction of the two-chambered heart, consisting of an atrium and a ventricle. Venous blood containing carbon dioxide passes through the heart. 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 of the 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;

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. Thin-walled blood vessels branching into capillaries run inside them. 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.

VISUAL ORGANS

The structure of the fish's eyes is adapted to allow them to see well at close range in their normal position. We can say that Pisces are nearsighted. True, they can see in several directions at the same time. If a fish wants to look at an object, it is forced to quickly turn around so that it comes into the field of view wallpaper: eye. Directly in front of the fish there is a narrow cone-shaped space that it sees with both eyes at once.

The retina in fish contains the same type of cells as in humans. Under experimental conditions, it has been established that some species of fish are able to distinguish over 20 colors. Vision is better in predatory fish. In some typical schooling fish it is rather weak, and their ability to distinguish colors is also less developed.

The fish has a wide all-round view, but it clearly distinguishes only objects located in the sector in front of it.

The pike sees a space of a smaller circle above the water. Keep this in mind when fishing for shy fish.

The nostrils of fish are lined on the inside with folded tissue, which contains nerve cells that perceive odor. Substances that have an odor and are dissolved or suspended in water enter the nostrils along with the water and irritate the olfactory tissue. In some species of fish, water enters the nostrils through breathing, not necessarily during swimming.

In general, fish have a good sense of smell, but some fish species have a better sense of smell and others have a worse sense of smell. Pike, for example, have a rather weak sense of smell, since the area of ​​folded tissue in the nasal cavity is small. The eel has a good sense of smell - for the opposite reason.

Fish exhibit a distinct reaction of wariness or aversion to the odors of sweaty palms, tobacco, refinery products (gasoline and lubricating oils), the odors of certain fish-eating animals, and some plant species. Care must be taken to ensure that substances that disgust fish do not get on bait and fishing tackle. For most fish, the sense of smell is more important than vision.

The taste organs are represented by taste buds with groups of sensitive cells located, in addition to the mouth, on the antennae and in different places on the surface of the body, so that fish are able to taste the food before it enters their mouth.

HEARING ORGANS

Fish have no outer or middle ear. Sound in the form of vibrations is transmitted from the swim bladder to the inner ear through a series of small bones of the skull. Sound travels nearly five times faster in water than in air, making it difficult for fish to determine the source and direction of sound, especially high-frequency sound. She feels low sounds along the lateral line. In this case, it is easier for her to determine the source of the sound.

In the inner ear of the fish there is an organ of balance: three on different levels located semicircular canals and adjacent extensions, in which there are “pebbles” - otoliths. They give the fish signals about its position in the water.

LATERAL LINE - SEISMOSENSORY ORGAN

The lateral line system consists of a main channel, usually located along the body, communicating with water through holes in the scales. Sensitive cells of the lateral line react to? changes in water pressure and transmit signals to the brain.

On the sides and on the head of the fish - in the upper and lower jaws, around the eyes and in the gill covers - there are also channels of the lateral line system in contact with water.

With the help of a seismosensory sense organ, a fish is able to avoid stationary objects, avoid unwanted encounters, maintain contact with individuals of its own species, and determine the location of prey, even if it does not see all this. The fish also determines the direction of water flow by its lateral line.

Nervous system. The central nervous system (CNS) consists of the brain and spinal cord (Figure A). The brain has five sections: the forebrain, diencephalon, midbrain, cerebellum and medulla oblongata (Fig. B).

A - general diagram: 1 - cranial nerves; 2 - brain; 3 - spinal cord; 4 - spinal nerves;

B - diagram of the brain: 1 - forebrain; 2 - diencephalon; 3 - midbrain; 4 - cerebellum; 5 - medulla oblongata

The medulla oblongata smoothly passes into the spinal cord. The peripheral nervous system is represented by nerves connecting the central nervous system to organs. The cranial nerves arise from the brain. They ensure the functioning of the senses and some internal organs. The spinal nerves arise from the spinal cord. They regulate the coordinated functioning of the muscles of the body, organs of movement, and internal organs. The nervous system coordinates the activities of the entire organism and the animals’ adequate reactions to environmental influences.

7th grade

Lesson on the topic "Internal structure of fish."

Objective of the lesson: Introduce students to supporting motor system, respiratory, circulatory, digestive and nervous systems of fish, using the example of river perch.

Lesson Objectives
Educational.

Show the similarities and differences in the structure of fish and lower chordates.

Give an idea of ​​the complexity of the internal structure of fish compared to lower chordates.

Give an idea of ​​the musculoskeletal, respiratory, circulatory, digestive and nervous systems of fish.

Developmental.
To develop students’ ability to compare representatives of different groups of animals, to evaluate the complexity of their overall organization and individual organ systems.
Educational. Foster a humane attitude towards animals, love for native land.

Lesson type
1) by purpose - a lesson in communicating new knowledge;
2) in content - a lesson in studying the internal structure of fish;
3) by type - combined lesson
.
Methods: Story, working with slides, conversation, independent observations.

Equipment: Multimedia projector, screen, laptop, presentation, tables “Internal structure of fish” and “External structure of fish”, fish brain, live fish.

Lesson Plan

1. Communicate the topic and objectives of the lesson

2. Checking homework

3. Explanation of new material

4. Consolidation of concepts independent observations

5. Execution Laboratory work

6. Summing up the lesson.

7. Homework

Lesson progress

1. Org. moment . Communicating the topic and objectives of the lesson Slide 1

2.Checking homework.

1) Oral survey according to the table Structure of fish Slide 2.

Choose the correct answers:

A - one class

fish, bony fish.

A - they breathe with gills

B – have a chord

B – head, chest, abdomen

B – head, body, tail

A - do not have glands

B – covered with scales

A – olfactory organ

B – taste organ

B – lateral line

G – hearing organ

A – sense of smell

B – touch

A – method of reproduction

B – they have a skeleton

8. Fish are of the following type:

A – chordates

B – hemichordates

B – skullless

G – vertebrates

Answers to the test on the topic“Pisces superclass. External building"

1. B 2. A, D 3. C 4. B, C 5. A 6. D 7. C 8. A

3.Explanation of new material

In this lesson we will get acquainted with the internal structure of fish using the example of river perch, find out whatmusculoskeletal system and the shoulder girdle, what is called swim bladder and how are gills arranged? . We will also talk about why some vessels are called veins, and others arteries, as the largest is called blood vesselperch organism, what It has parts of the brain and sensory organs.

(Story using presentation)

Let's consider the internal structure of bony fish using the example of river perch.

The body of the perch has a well-developed musculoskeletal system. Let's find out what it is.Musculoskeletal system- This special system of the animal body, which provides the ability to move in space with the help of muscles, serves as a place for their attachment, being a support and protection for all organs of the body. As you already understand, the musculoskeletal system includes the skeleton and muscles of the animal.

Writing in workbooks: the musculoskeletal system includes the skeleton and muscles of the animal

Slide 3.

The skeleton of a perch consists of large number bones. The basis of the skeleton is the spine, formed by a large number of vertebrae and penetrating the body of the fish from the head to the tail. In the perch developing in the egg, a notochord is first formed, around which vertebrae are later formed. In an adult, only small cartilaginous formations between the vertebrae remain from the notochord. The number of vertebrae in the body is usually approximately the same in individuals of the same species, and in river perch it ranges from 39 to 42. Perch, like most fish, has a skeleton of a skull, ribs and fins (paired and unpaired). The skeleton of unpaired fins (caudal, anal and two dorsal) consists of bony rays that form the basis of the fin blades. Paired fins have support in the body in the form of limb girdles - shoulder (for pectoral) and pelvic (for ventral fins). The limb girdle is a special formation that connects the free limb (fin) to the spine. The muscles of the perch are quite well developed, the strongest muscles are located on the back and tail of the animal.

Recording in workbooks:spine, skeleton of the skull, ribs and fins (paired and unpaired). The strongest muscles are located on the back and tail.

Slide 4

Like any fish, perch is much heavier than water, which is why it needs a special organ that can provide the animal with buoyancy, that is, the ability not to sink in water. This organ is called the swim bladder.swim bladderis a translucent sac filled with a mixture of gases and located in the abdominal cavity above the intestines. The swim bladder is formed even in the embryo, like an outgrowth of the intestine on the dorsal side of the fish. 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, then she will not be able to swim and will die. In adult perch, the connection between the bladder and the intestine is lost. Fish can regulate the volume of the swim bladder, thereby controlling the depth of their dive, either narrowing or expanding it.

Writing in workbooks: The swim bladder is a translucent sac filled with a mixture of gases and located in the abdominal cavity above the intestines. By adjusting the volume of the swim bladder, fish can control the depth of their dive.

Slide 5

Digestive system.Speaking about river perch, we should not forget that this animal is a predator. It captures, holds and crushes prey with teeth sitting on the jaws. Next, the food passes through the pharynx and esophagus, after which it is digested in the stomach under the influence of gastric juice. Then the partially crushed food enters the small intestine, where it is broken down under the influence of the digestive juice of the pancreas and the bile produced by the liver. The supply of bile accumulates in the gallbladder. Afterwards, the nutrients penetrate directly through the intestinal walls into the blood, and all undigested residues enter the anus through the hind intestine and are excreted from the body.

Writing in workbooks: Mouth – tongue – pharynx – esophagus – stomach (liver, pancreas) – intestines – anus.

Slide 6

Respiratory system.Fish breathe oxygen dissolved in water. Breathing is carried out using gills. First, the perch swallows water, then, passing it through the gills, filters oxygen and removes excess water. The gills consist of gill arches, each of which, in turn, consists of gill filaments on one side and gill rakers on the other. The stamens prevent prey from leaking through the gills, and the petals are connected to the circulatory system and exchange oxygen and carbon dioxide between the body of the perch and environment. This process is called gas exchange. The spaces between the gill arches are called gill slits. Externally, the gills of the perch are protected by gill covers

Writing in workbooks: The gills are formed by gill arches, which consist of gill filaments on one side and gill rakers on the other.

Slide 7

Circulatory system.Blood carries nutrients received from the intestines and oxygen received through the gills throughout the body of the river perch. The circulatory system is closed. The heart is two-chambered: it consists of one atrium and one ventricle. Bright scarlet blood saturated with oxygen comes out of the ventricle and is sent to the tissues and cells of the body through vessels called arteries. Cherry blood, saturated with carbon dioxide and decay products, moves back to the heart through vessels called veins. The largest blood vessel in the fish body is the aorta.

Writing in workbooks: The circulatory system is closed. The heart is two-chambered: it consists of one atrium and one ventricle. From the ventricle, arterial blood goes through the arteries to the organs, and from the organs through the veins, venous blood goes to the atrium.

Slide 8

Excretory system.The kidneys filter waste products from the blood, forming urine. Through two ureters it enters the bladder, from which, after accumulation, it is excreted directly behind the anus.

Writing in workbooks: kidneys, ureters, bladder, urinary opening.

Slide 9

Nervous system The perch is represented by the spinal cord and brain. The spinal cord is located in the spinal canal. Between each pair of vertebrae, nerves arise from it that control the functioning of the muscles, fins and organs of the body. The brain is divided into a number of sections, namely: the forebrain, diencephalon and midbrain, cerebellum and medulla oblongata. Each department is of great importance in the life of an animal. For example, the cerebellum is responsible for balance and coordination of movements. The medulla oblongata gradually passes into the spinal cord and plays a large role in controlling breathing, blood circulation, digestion and other important functions of the body.

Writing in workbooks: Brain (anterior, intermediate, middle, cerebellum and medulla oblongata) and spinal cord.

Slide 10

Perch also has sense organs. So, olfactory organare paired blind sacs with sensitive cells located in them. Paired nostrils lead into the blind sacs, which are located at the front end of the head.

Organ of vision are the eyes; It is important to note that perch sees well enough only at a relatively short distance.

Hearing organs are not visible from the outside, since they are located on the sides of the head inside the skull itself.

Organs of taste are sensitive cells located not only in the mouth, but throughout the entire surface of the body.

The lateral line is a special sensory organ, located on the sides of the body and running from the head to the tail of the perch. The lateral line allows you to sense temperature and current speed, and also allows you to sense the approach of other animals.

Writing in workbooks: Sense organs: smell, vision, hearing, taste, lateral line.

4. Reinforcement of concepts

Slides 11 – 14 frontal work with drawings and tests

5. Completing Laboratory work No. on page 160 of the textbook.

6. Summing up the lesson.

All representatives of the Superclass of fish have a number of structural features, both external and internal. Some of these features apply to all fish, others - only to some of them. The most noticeable differences in structure are observed between representatives of the two main Classes of fish, namely: representatives of the Bony Fish Class and representatives of the Cartilaginous Fish Class. River perch belongs to the Class Bony fish.

7. Homework.

1. Study § 32 pp. 155 – 161;

2. Answer questions 1-4 orally;

3. Prepare a multimedia abstract on one of the proposed topics:
1. Variety of fish.

2. Giant fish and dwarf fish.

3. Coloring of fish in connection with their lifestyle.

Appendix 1.

Test on the topic “Superclass Pisces. External structure of fish."

Choose the correct answers:

1. Fish are animals that are classified as:

A - one class

B – two classes: Cartilaginous fish and Bony fish

B – three classes: Cartilaginous fish, Semi-cartilaginous fish and Bony fish

D – four classes: Cartilaginous fish, Semi-cartilaginous fish, Bony fish

fish, bony fish.

2. Fish are adapted to their habitat:

A - they breathe with gills

B – have a chord

B – have a brain and spinal cord

G-paired limbs have the shape of fins

3. What sections does the fish body consist of:

A – cephalothorax, abdomen, tail

B – head, chest, abdomen

B – head, body, tail

G – head, body, fins

4. What are the structural features of fish skin?

A - do not have glands

B – covered with scales

B – has many mucous glands

G – has no covering formations

5. Fish have a special sense organ that perceives the direction and strength of water flow:

A – olfactory organ

B – taste organ

B – lateral line

G – hearing organ

6. The lateral line organs in fish perform the following functions:

A – sense of smell

B – touch

B – only sensations of the depth of immersion

D – sensations of depth of immersion, direction and force of water flow

7. The flattened body shape of bottom fish indicates:

A – method of reproduction

B – they have a skeleton

B – adaptability to the environment and habitat

D – they have a protective coloring

8. Fish are of the following type:

A – chordates

B – hemichordates

B – skullless

G – vertebrates

We recommend starting to become familiar with the internal structure of bony fish by studying the features of the location of systems and organs using the materials presented in the lesson manuals, look at the pictures and diagrams. After theoretical preparation, proceed to the task on fish dissection .

Digestive system bony fishes, compared to cartilaginous fish, has a number of differences. Overall, she less differentiated than in cartilaginous fish, especially in the intestinal area, where practically there are no clear boundaries between its departments.

The digestive tract begins oral cavity , in which they are located language (as in cartilaginous fish, does not have its own muscles) and bone teeth. The shape and number of teeth vary considerably among different species. Predatory fish have numerous sharp teeth, directed with their ends somewhat back, towards the pharynx, which helps to hold slippery prey. Some fish have teeth small needle-shaped(herring, carp species).

Some bottom fish (pufferfish, flounder, wrasse, etc.) have teeth in in the form of large plates, with the help of which dense plant tissues are crushed, shells and shells of benthic species (crustaceans, echinoderms) are crushed. This is also facilitated by powerful pharyngeal teeth, sitting on the last pair of gill arches.

Throughout life there is change of teeth, but it is irregular. In this case, new teeth grow in the spaces between existing teeth. Planktivorous fish(herring, carp) are deprived dental apparatus and have a peculiar filter device in the form of gill rakers that help filter plankton.

The oral cavity is followed wide throat , short esophagus , passing Vstomach . The size and shape of the stomach are determined by the type of food. U predatory fish (perch, pike) the stomach is more voluminous, with easily extensible walls and sharply demarcated from the intestine. Against , boundaries between the stomach and intestines herbivores fish (species of carp fish - silver carp, grass carp, etc.) little noticeable.

departs from the stomach intestines in the form of a long round tube forming a loop, but without external divisions into departments. In front small intestine there are special formations - pyloric growths, which delay the passage of food and increase the absorption surface of the intestine. In fact, they perform the same function as the spiral valve of cartilaginous fish. River perch has only three pyloric outgrowths, but in some fish (salmonids) their number reaches two hundred.

Anterior section the small intestine is duodenum, where do they flow liver ducts andpancreas. The liver is well developed in all fish. Entering the small intestine bile with the enzymes it contains, it promotes active digestion of food. In addition, the liver produces urea, accumulates glycogen. It also plays an important role in neutralizing toxic substances ( barrier organ).

Pancreas in many fish it is represented in in the form of small fat-like formations, lying on the mesentery in the bends of the intestinal tube. In some fish (pike) it is more compact.

Small intestine imperceptibly turns into thick, next comes rectum which ends anus.

Respiratory system bony fish gill type, presented four pairs gills; fifth – unpaired and greatly reduced. In the gill apparatus, unlike cartilaginous fish, no partitions separating the gills. The basis of each gill is arc(Fig. 26), on internal the side on which the short bones are located stamens, representing a filtering apparatus. It prevents food from coming back out.

WITH external the sides of the arc are soft gill filaments where capillaries branch and gas exchange occurs. Attached to the inner side of the gill cover is a rudimentary falsebranch, lost the function of gas exchange. Gill cover, covering the opening leading to the gills, is a hard plate consisting from several bones elements.

Breathing mechanism bony fishes are carried out mainly due to the movements of the gill cover, which ensures a constant flow of water through the mouth and gill apparatus. When inhaling, the gill covers move to the sides, and their thin leathery membranes are pressed against the gill openings. Due to this, a space with reduced pressure is formed in the peribranchial cavity; water enters the oropharyngeal cavity through the mouth opening and washes the gills. At reverse movement excess pressure is created on the lids and water, bending their leathery edges, comes out through the holes.

With this method of breathing, fish are able to absorb up to 46–82% oxygen, dissolved in water. Some fish living in oxygen-deficient waters develop and other devices: cutaneous respiration can account for up to 20–30% or more of the total gas exchange; there are fish that additionally use atmospheric oxygen, capturing air with your mouth from the surface of the water.

Circulatory system bony fish (Fig. 27), compared to cartilaginous fish, different a number of signs. Instead of an arterial cone, it departs from the ventricle aortic bulb, which has smooth muscles and is the beginning of the abdominal aorta. In the area of ​​the gill apparatus only four pairs of afferents and efferents arteries.

The venous system has also undergone changes: no side veins; occurs in many species asymmetry of the renal portal system- only left cardinal vein forms a capillary network in the kidney tissue, the right cardinal vein passes through the kidney without interruption.

On the ventral side of the front part of the body is located heart , which is contained in pericardial sac. TO atrium , having smooth muscles and a dark burgundy color, adjacent venous sinus where venous blood collects. Departs from the atrium ventricle , characterized by a bright red color and thick muscular walls. The difference in coloring of the atrium and ventricle is due to the thickness of the walls - venous blood is visible in the thin-walled atrium.

Departs from the ventricle abdominal aorta, the beginning of which is aortic bulb. Blood from the abdominal aorta gill bearers arteries is sent to the gills, where it is enriched with oxygen, then along enduringgill arteries flow into steam rooms aortic roots. From the roots of the aorta are formed carotid arteries and dorsal aorta, breaking up into smaller arteries that carry blood to organs and tissues (in an opened fish, the dorsal aorta is clearly visible between the kidneys).

From the back of the body, venous blood collects through unpaired caudal vein, which splits into paired rear cardinal. Moving away from the head anterior cardinal(jugular), which at the level of the heart merge with the posterior cardinal veins to form Cuvier's ducts. The portal system is present only in the left kidney (see above). The portal system of the liver is formed by unpairedsubintestinalvein. From the liver, venous blood enters the hepatic veins into the venous sinus.

Excretory system. Excretory organs of bony fish similar to those of cartilaginous fish, however not related to the reproductive system. Trunk buds (mesonephros) long, dark red in color and located on the sides of the spine above the swim bladder. The ureters serve willfov channels, which stretch along the inner edge of the kidneys. Bony fish have bladder .

Reproduction system. Bony fish are dioecious; As a rare case, there is a manifestation of hermaphroditism (sea bass). The reproductive system is represented in males testes , in females - ovaries . The gonads of both males and females have independent ducts. In males wolf channel performs only the function of urination. Elongated structures extend from the ovaries, ending in a genital opening through which eggs are laid out ( Müllerian canals are absent).

Central nervous system and sensory organs.

Like other vertebrates, central nervous system consists of head And spinal sections.

Brain in bony fishes, in general, relatively larger in size, but of a more primitive structure than that of cartilaginous fish: forebrain relatively small, in his roof absent nervous substance, cavities cerebral hemispheres (lateral ventricles) not separated partition . The most pronounced development midbrain and cerebellum.

Forebrain looks like small hemispheres in which there is no brain matter (their epithelial roof). The main part of the hemispheres consists of the so-called striatum, lying on the bottom. In the front are olfactory lobes, the sizes of which are inferior to those of cartilaginous fish.

Diencephalon covered by the anterior and middle parts of the brain. There is a small gland in its back internal secretion – pineal gland and on the lower side there is a rounded outgrowth - pituitary.

Midbrain has large optic lobes , where incoming processing takes place visual information, and the abdominal part contains communication centers with the cerebellum, medulla oblongata and spinal cord.

Cerebellum overlaps the midbrain and significantly covers the beginning medulla oblongata, which has rhomboid fossa(fourth ventricle). The cerebellum determines the activity of somatic muscles, the activity of movement and the maintenance of balance.

Like cartilaginous fish, from the brain ten pairs of nerves arise , coordinating the work of systems and organs.

The spinal cord does not have any special differences in comparison with cartilaginous fish, but the autonomy of its functions is less pronounced.

Sense organs bony fish are diverse, but the most important in their life are smell and taste.

Despite the weak development of the olfactory lobes of the forebrain, compared with cartilaginous fish, the resolution in capturing smells in most bony fishes it is quite high, especially in schooling and migratory fishes. This is due to the special structure olfactory bags which have well-developed folds olfactory epithelium And flickering eyelashes, increasing the flow of water through the nasal openings.

Taste buds, defining the function taste , located in the oral mucosa, on the antennae, body surface and fins. They allow you to clearly recognize all taste sensations - bitter, sweet, sour and salty.

Lateral line organs well developed and represent channels passing through the thickness of the skin. With the help of small holes in the scaly cover of fish, they communicate with the external environment. Thanks to the sensory cells of the canal walls, fish receive information about water fluctuations, navigate its currents, and determine the location of prey or dangerous objects.

Touch function performed by clusters of sensory cells (“tactile corpuscles”), scattered over the entire surface of the body. There are especially many of them concentrated near the mouth - on the antennae, lips, and also on the fins, which allows the fish to feel the touch of hard objects.

In the superficial layers of the skin there is thermoreceptors , with the help of which fish perceive temperature changes in the environment with an accuracy of 0.4 degrees. On the head of the fish there are receptors, catching changes electric and magnetic fields and, thus, promoting spatial orientation and coordination of actions of individuals of schooling fish.

A number of species have electrical organs, which are modified areas of the body’s muscles. They can be located on the head, sides and tail of fish, determining orientation towards other individuals, methods of defense and attack. They serve as receptors "neuroglandular cells" located on the body and in the lateral line channels.

Vision mainly helps fish in short-range orientation(up to 10–15 m), because due to the structure of the eye they are “myopic”: the lens is spherical, the cornea is flat, the accommodation of the eye is insignificant. However, the retina of the eyes of bony fishes contains not only sticks(black and white vision), but also cones, defining color perception. Vision is important when searching for food, protecting from danger, and intraspecific communication, especially during the breeding season.

Organ of hearing and balance presented only inner ear, which is surrounded by a cartilaginous capsule with its external ossification. The basis of the inner ear is membranous labyrinth with three semicircular canals and an oval sac, what makes up the vestibular apparatus, or organ of balance. Next to it is the actual organ of hearing - round pouch , equipped with a hollow outgrowth - lagena. The sensory cells of the lagena and saccules serve as sound receptors. Inside the sacs and lagena lie auditory pebbles, or otoliths, enhancing the perception of information about body position. In a number of fish, the vestibular apparatus is connected to the swim bladder, which increases sensitivity when maintaining balance.

general arrangement of internal organs .

Directly under the operculum visible four pairs gills arcs are bright red. Behind them is two chamber heart with the aortic bulb, from which it originates abdominal aorta, carrying blood to the gill apparatus. Between the gill cavity and the abdominal cavity there is thin vertical partition.

Located in the anterior part of the abdominal cavity liver, under which lies stomach with the one moving away from him intestines. At the beginning of the intestinal tube, finger-shaped pyloric growths(perch has three). Pancreas in most fish, in the form of lobules, it is located on the mesentery at the level of the stomach and the beginning of the intestine. In one of the intestinal loops there is maroon spleen(contains hematopoietic and lymphoid tissues).

Lies under the spinal column swim bladder, which represents hydrostatic organ, allowing the fish to change the position of its body in the water column. Functionally it is connected with inner ear, which allows the fish to determine external pressure and, transmitting its changes to the auditory apparatus (otoliths), maintain balance. In some fish, the swim bladder takes part in gas exchange and can contribute to the production of sounds.

Closer to the tail are the genitals - testes or ovaries. Testes smooth, milky cream color, which is why they got the name milk. Ovaries have granular structure and yellowish-orange color.

Rice. 29. External and internal structure of perch:

1 – mouth with teeth, 2 – gill cover, 3 – bony scales, 4 – homocercal caudal fin, 5 – anal fins, 6 – eyes, 8 – nostril, 9 – lateral line, 10 – anus, 11 – genital opening, 12 - excretory opening, 13 - open stomach, 14 - intestine, 15 - pyloric outgrowths, 16 - rectum, 17 - liver, 18 - gall bladder, 19 - pancreas, 20 - gills, 21 - spleen, 22 - swim bladder , 23 – kidneys, 24 – ureters, 25 – bladder, 26 – ovaries, 27 – atrium, 28 – ventricle, 29 – aortic bulb

Date: 02/14/2017 Date: 02/18/2017

Class: 7 "A" "B"

Subject: Biology

Lesson on the topic "Internal structure of fish."

Lesson objectives:

Educational.	Show the similarities and differences in the structure of fish and lower chordates.
b) Give an idea of ​​the complexity of the internal structure of fish compared to lower chordates.
c) Give an idea of ​​the respiratory system, circulatory system of fish, digestion, nervous and reproductive systems. Developmental. To develop students’ ability to compare representatives of different groups of animals, to evaluate the complexity of their overall organization and individual organ systems. Educational. To foster a humane attitude towards animals and love for one’s native land. Lesson Objectives 1. Introduce students to the respiratory, circulatory, digestive, and reproductive systems of fish. 2. Continue to formulate the concept of evolution, the relationship between the organism and the environment, individual development, about the taxonomy of the animal world. 3. Deepen the concept of metabolism. Methods: Story, working with slides, conversation, independent observations. Equipment: laptop, disk with slides on the topic: "Fish". Lesson Plan

Lesson progress

1. Org. moment.Communicate the topic and objectives of the lesson

Frontal survey:

Card survey:

Preparing to study new material. The teacher reports on the continuation of the study of the internal structure and life of fish. In the process of studying, it will become known how the fish feeds; how blood circulation occurs; how does a fish breathe? how it develops.

2.Explanation of new material

Teacher. We have studied external structure fish, and today we will study the internal structure of fish. (Slide show "Cutaway fish")

Digestive system.
River perch is a predator. It feeds on a variety of aquatic animals, including small fish. It catches its prey in its mouth, holding it with the help of sharp teeth located on its jaws. The mouth leads into the pharynx, which is pierced by vertical gill slits. In the front part of the pharynx, at the bottom, lies a fleshy tongue, which serves as an organ of touch. From the pharynx, food enters the esophagus and then into the stomach. Because the bass swallows its prey whole, its stomach can become very distended. Gastric juice is secreted in the stomach, under the influence of which food begins to be digested. From the stomach, food enters the long small intestine. The perch has three blind processes developed in its front part. They increase the suction surface and slightly slow down the speed of food movement. The ducts of the liver and gallbladder, as well as numerous ducts of the pancreas, flow into the intestines. Under the influence of their secretions, food is finally digested and absorbed. Undigested residues enter the hindgut and are expelled through the anus.

Respiratory system. (Slide show) Fish breathe oxygen dissolved in water. Their respiratory organs are gills, located on the walls of the pharynx between the gill slits. The gills of fish consist of a gill arch. On the side facing the body cavity there are small gill rakers, and on the opposite side there are numerous gill filaments. The gill rakers are a filtering apparatus. They prevent the booty from slipping out

through the gill slits. A dense network of capillaries is developed in the gill filaments. Through their thin walls, oxygen from the water penetrates into the blood, and carbon dioxide from the blood into the water.

Circulatory system. (Slide show) Like the vast majority of chordates, the circulatory system of fish is closed. Its central organ is the heart, lying on the ventral side of the body. Several large vessels leave the heart. Those through which blood moves from the heart are called arteries. Large arteries are called aortas. The vessels through which blood enters the heart are called veins. The heart of fish consists of two chambers: one atrium and one ventricle. Their muscular walls alternately contract, ensuring the movement of blood through the vessels. The ventricle has a special valve that prevents blood from flowing back.

Nervous system (slide)

The fish brain is usually divided into three large parts: the forebrain, the midbrain and the hindbrain. The forebrain consists of telencephalon and diencephalon. At the rostral (anterior) end of the telencephalon are the olfactory bulbs, which receive signals from the olfactory receptors. The olfactory bulbs are usually enlarged in fish that actively use their sense of smell, such as sharks. The optic lobes are located in the midbrain cortex. The posterior section is divided into the hindbrain itself (which includes the pons and cerebellum) and the medulla oblongata. Thus, fish, like other vertebrates, have five parts of the brain (from front to back): terminal, intermediate, middle, posterior and medulla.

The spinal cord runs within the neural arches of the vertebrae along the entire length of the fish's spine. Similar to the myomeres and the spine, segmentation is observed in the structure of the spinal cord. In each body segment, sensory neurons enter the spinal cord through the dorsal roots, and motor neurons exit it through the ventral roots.

Swim bladder. (Slide) In the upper part of the internal cavity of the perch, above the intestines, there is a voluminous swim bladder, which looks like a translucent sac filled with gas. Its main function is to provide positive buoyancy to the fish, since it is heavier than water. The swim bladder is surrounded by a dense network of blood vessels, from which gas is released into it. As the volume of the swim bladder increases, the body density of the perch decreases, and it floats to the surface of the water. When the volume decreases, on the contrary, the body density increases and the fish sinks to the bottom. The swim bladder develops as an outgrowth of the dorsal wall of the intestine.

Fish have developed a special hydrostatic organ - the lateral line. It looks like a series of small pores stretching along the body from head to tail. The pores lead into a canal that is located in the skin. Numerous nerve endings approach it. Using the lateral line, fish evaluate the direction and strength of the water current, the depth of immersion and the approach of various objects to them. The lateral line is absent only in representatives of the herring order, since organs that perceive water pressure develop in their gill covers.

4. Consolidation of concepts, independent observations.

4.1. Students are given cards with questions for each organ system. The teacher invites you to familiarize yourself with the content of the questions, and in the process of viewing slide show mentally answer them. (The teacher now shows the individual slides as a slide show.) After viewing, the teacher has one student read the digestive system questions aloud and answer them using the slide on the screen. All other systems are studied in the same way.

4.2. Show the slide “Structure of fish” - on this slide the internal organs of the fish are numbered. Students must figure out what number, what organ, what system it belongs to.

Homework, assessment

Paragraph 41, answer A, B, C and paraphrase