Biology at the Lyceum. Musculoskeletal system (skeleton) of fish

The musculoskeletal system forms the morphological basis of movement. Muscles are the actual mover. It is in the muscle that the transformation of the chemical energy of ATP into mechanical energy occurs. However, a muscle needs a fulcrum to contract and produce movement. The bones of the skeleton act as such points of support for the numerous muscles of the fish. The skeleton also performs a shaping function (Fig. 5.1).

The structure of the skeleton of fish (Fig. 5.2). By the variety of body shapes of fish, one can also judge the complexity of the structure of their skeleton (Fig. 5.2). A feature of fish is that many of them have both an internal and an external skeleton, traditional for all vertebrates. The latter can be seen as a sign of evolutionary stagnation. In bony fish, the external skeleton is only scales. However, in sturgeons, the external skeleton is quite well developed. Actually, their scales are present only on the caudal peduncle, and the torso and head bear bone formations - bugs, plaques, spines and spikes inherited modern fish from their ancestors - armored fish. In fish, the requirements for bone stiffness and strength are lower than in terrestrial vertebrates. It should be noted that and relative mass bones in fish are 2 times less. The size of the skeleton of bony fish varies in proportion to body weight. This dependence can be described by the regression equation:

M sc \u003d 0.033 M of the body 1.03,

where M sk is the mass of the skeleton, g; M body - body weight, g.

A smaller bone mass is very important for aquatic animals. Having a large specific gravity, bone tissue significantly affects the buoyancy of the body of aquatic animals. Therefore, even secondarily aquatic animals (cetaceans), in the process of their adaptation to the aquatic environment, received neutral buoyancy to a large extent due to the lightening of the skeleton.

The practically absent gravity in the aquatic environment explains the significant differences in the structure individual bones fish. So, fish do not have tubular bones, which are very durable. In tension, they withstand a force of 170mN / m 2, and even more in compression - 280 mN / m 2.

Rice. 5.1. Fish Body Shape:

1 mackerel; 2-garfish: 3-lesh; 4-moon-fish; 5-flounder; 6-eel; 7-marine needle; 8- herring king; 9-body; 10- hedgehog fish; 11- seahorse; 12-slope In water, such loads do not exist: the fish skeleton does not perform the function of supporting the body, as in terrestrial vertebrates. Their body is supported by the water itself: fish have neutral buoyancy (or close to neutral).

Rice. 5.2. Skeleton of fish (perch):

1 - skull bones; 2-4, 7, 10, 11 - fin bones; 5 - urostyle; 6 - tail vertebrae; 8 - trunk vertebrae; 9 - ribs; 12 - gill covers; 13 - upper and lower jaws

fish bones are also deprived of spongy substance, which is filled in terrestrial animals with red bone marrow. The latter is absent in fish, and other organs perform the function of hematopoiesis.

Fish bones are resilient and elastic, but not very strong structures. The bone has a well-developed organic matrix and a mineral part. The first is formed by elastin and collagen fibers and gives the bones a certain shape and elastic properties. Mineral components provide the necessary strength and rigidity of bone formations. The degree of mineralization of the bones of fish (bony) varies widely: from 20% in juveniles to 60% in old individuals, with the most active mineralization of the skeleton occurs in fish in the first year of life (Table 5.1).

5.1. Dependence of the total mineralization of the bones of carp underyearlings on the intensity of their growth, % of ash in the dry matter of the gill cover

Note. Average data for three reservoirs of the Moscow, Smolensk regions and Stavropol Territory.

In addition to age, bone mineralization is affected by species. In coeval individuals of carp, roach, perch and catfish from the same reservoir, the differences in the degree of mineralization of the gill cover reach 15%.

The degree of water mineralization (58-260 mg/l) and the nature of nutrition (including a 30-day fast) do not affect the level of ash in the bones of fish. However, the growth rate significantly affects this indicator. Underyearlings of carp grown under the same conditions, but differing in body weight, have large differences in the degree of mineralization of bone tissue.

The elemental composition of bone ash is less stable compared to the total mineralization and changes under the influence of the conditions of keeping the fish. For underyearlings of carp of different breed lines (naked, mirror, linear and scaly), the following averaged characteristics of the macro- and micromineral composition of bone tissue can be given (Table 5.2).

A significant proportion of mineral bone formations is represented by phosphorus compounds that are part of hydroxyapatite. The content of phosphorus in the bones of fish is 2 times lower than in terrestrial animals, but rather stable (about 10%). The Ca:P ratio in the bones of carp fingerlings is approximately 2.7:1. Magnesium in the composition of hydroxyapatite crystals ensures the strength of the bone tissue of terrestrial animals. In fish, the requirements for bone strength are different, so the level of magnesium in the bones is low (220 mg% instead of 1500 mg% in terrestrial animals). Fish also have a higher Ca:Mg ratio (114:1 in carp underyearlings and 50:1 in terrestrial domestic animals).

The micromineral composition of bones is not uniform. It is influenced by many factors (nutrition, age, species). However, the main factor should be considered alimentary. The ratio of the individual

trace elements in bone tissue under stable conditions for growing fish more permanently. So, most of all in the bones of zinc (60-100 mg% for ash), the second place is occupied by iron (15-20mt%), then manganese (7-16 mg%) and copper (1-5 mg%). Interestingly, the concentration of iron in water does not affect the accumulation of the element in the skeleton.

Concentration heavy metals in the bones directly determined by their prevalence in the external environment. The intensity of accumulation of heavy metals is higher in juveniles. The concentration of strontium (Sr90) in the bones of eared perch and tilapia can exceed its level in water by 10 times. In tilapia, already 2 days after keeping it in radioactive water, the level of bone radiation reaches the level of water radiation. After 2 months, the concentration of strontium in the tilapia skeleton was 6 times higher than that in water. Moreover, how easily heavy metals penetrate into the bone tissue of fish, just as slowly they leave it. Strontium remains in the skeleton of fish for decades, even if the fish are kept in an environment free of this element.

The skeleton of bony fish is usually divided into axial and peripheral (see Fig. 5.2). The axial skeleton includes the vertebral column (trunk and tail), ribs and head bones. The number of vertebrae different types varies and ranges from 17 for the moon-fish to 114 for the river eel. In cartilaginous fish - sea fox - the number of vertebrae reaches 365. The first four trunk vertebrae can be transformed into the so-called Weber apparatus. The vertebrae of the trunk and tail parts are not the same in structure. The trunk vertebra has a body, an upper spinous process and two lower spinous processes. at the base of the superior spinous process and top edge the vertebral body is the neural arch. Below, to the right and left of the trunk vertebrae, ribs extend, which are movably connected to the vertebrae.

The vertebrae of the caudal peduncle differ in that their inferior spinous processes fuse to form the hemal arch and unpaired hemal process. In addition, there are no costal bones in the tail.

Between the vertebral bodies are layers of gelatinous mass - the remnants of the chord, which provide elasticity and elasticity spinal column. Thus, the spine is not a single bone. It looks like a chain consisting of rigid elements - vertebrae and elastic disks. The vertebrae are movably connected to each other by means of elastic ligaments. This design of the spinal column provides greater mobility and elasticity of the spine in the horizontal plane. For fish, this is very important, since the translational movement of fish is achieved due to the S-shaped bends of the body and caudal peduncle.

The head skeleton has complex structure and unites more than 50 mostly paired bones (Fig. 5.3). It includes the bones of the skull and the visceral part of the head (the bones of the upper and lower jaws, 5 pairs of gill arches and 4 bones of the gill covers).

The peripheral skeleton is represented by the bones of the unpaired fins, the bones of the girdles of the paired fins, and also the muscular bones. The unpaired dorsal and anal fins are based on radials, to which the rays of the fins are attached.

Rice. 5.3. Main bones of the perch head:

1 - frontal; 2- parietal; 3- upper occipital; 4- nasal; 5 - premaxillary; 6 - upper jaw; 7- tooth; 8- joint; 9 - prelid; 10- cover; 11 - intercover-12 - undercover; 13 - posterior temporal; 14 - preorbital; 15- orbital bones

Paired fins (Fig. 5.4) - pectoral and ventral - have their own skeleton, which is represented by the bones of the free fin and the bones of the corresponding girdle (shoulder or pelvic). The shoulder girdle of bony fishes consists of the scapula, coracoid, three bones of the cleithrum, and the posterior temporal bone. The posterior temporal bone is an element of the skull and therefore gives the shoulder girdle strength and relative immobility, which is enhanced by the immovable connection of the cleithrums of the right and left halves of the body.

The pelvic girdle (girdle of the ventral fins) is not rigidly connected to the axial skeleton. It consists of two (right and left) triangular bones to which the fins are attached. The bone base of the pectoral and ventral fins is not the same. The composition of the pectoral fins includes three types of bone formations: basal. multiple radials and fin rays.

Rice. 5.4. Bones of paired fins and their girdles:

a-cartilaginous fish; b-bony fish; I-pectoral fin by the shoulder girdle; II - ventral fin with pelvic girdle; 1 - scapular; 2- coracoid section; 3-basals; 4-radials; 5 - rays of fins; 6 - pterygopodia; 7-blade; 8 - coracoid; 9-clerum; 10-back clayroom; 11 - overkleytrum; 12-posterior temporal bone; 13- pelvic bone

In the pelvic fins of bony fish, radials are usually absent. It should be emphasized that, in general, the supporting part of the pectoral fins is more perfect. They also have a more developed muscular system. That is why the pectoral fins provide complex behavioral acts.

Fish are the largest group of aquatic chordates in terms of species diversity, which is also the most ancient. Fish inhabit almost all fresh and salt water bodies. All their organ systems are adapted to living in the aquatic environment. According to accepted science, they belong to the Eukaryote domain, the Animal kingdom and the Chordata type. Let's take a closer look at the superclass.

body integuments

The outer covering of the fish's body is skin and scales. There are rare exceptions when the scales are missing or modified. The skin is divided into dermis and epidermis. The epidermis of the superclass Pisces is not keratinized.

In the formation of scales leading role does the dermis. The scales are different depending on the class of fish to which it belongs.

• available in the class Cartilaginous fish. It consists of dentin covered with enamel. It is this kind of scales that in the course of evolution turned into the teeth of sharks and rays. If a link of scales is lost, it will not be restored.
• Ganoid scales are characteristic of the Sturgeon order. It is a bone plate coated with ganoin. Such a shell perfectly protects the body.
• Cosmoid scales are observed in lobe-finned and lungfish individuals. It consists of cosmin and dentin.

The coloration of individuals of the superclass Pisces can be very diverse. Representatives of the fauna can be either painted in one color or be variegated, they can have a dull or, conversely, color that warns of danger.

Musculoskeletal system

The musculoskeletal system allows the fish to move and change position in environment. The skeleton of a fish is different from that of a land animal. Her skull has over forty elements capable of moving independently. This allows the animal to stretch and spread its jaws, sometimes very widely.

The spine is made up of individual vertebrae that are not fused together. It is divided into the trunk and tail sections. When swimming, the driving force is created by the fin of the fish. They are divided into paired (thoracic, abdominal) and unpaired (dorsal, anal, caudal). In bone representatives of the superclass, the fin consists of bone rays, which are united by a membrane. Muscles help to unfold, fold and fold it, as the fish wants.

Swimming of the inhabitants of the aquatic environment is possible thanks to the muscles. They contract and the fish move forward. Musculature is divided into "slow" and "fast" muscles. The first are needed for calm swimming, drifting. The second - for fast and powerful jerks.

Nervous system of fish

The brain of fish is divided into sections. Each of them performs a specific function:

1. The forebrain consists of the intermediate and final. The olfactory bulbs are located in this section. They receive signals from external bodies smell. Fish that actively use the scent while hunting have enlarged bulbs.
2. The midbrain has optic lobes in its cortex.
3. The hindbrain is divided into the cerebellum and medulla.

The spinal cord in representatives of the superclass Pisces runs along the entire length of the spine.

Circulatory system

Most representatives of the superclass have one circle of blood circulation and a two-chambered heart. The circulatory system is closed, it conveys blood from the heart through the gills and body tissues. does not separate the oxygen-enriched arterial blood from poor venous.

In fish, they follow each other and fill with venous blood. This is the venous sinus, atrium, ventricle, arterial cone. Blood is able to move only in one direction - from the sinus to the cone. Special valves help her with this.

Organs of gas exchange in fish

The gills of a fish main body gas exchange. They are located on the sides of the oral cavity. At bony fish they are covered with a gill cover, in others they can freely open outward. When ventilation of the gills occurs, water passes into the mouth, then into the gill arches. After that, it again goes out through the openings of the gills in fish.

The structure of the gills is as follows: they have semi-permeable membranes penetrated by blood vessels, and are located on bone arches. Gill filaments, penetrated by the smallest network of capillaries, help the fish to feel even more freely under the water column.

In addition to gill breathing, fish can use another method of gas exchange:

• Fish larvae can carry out gas exchange through the surface of the skin.
• Some species have lungs that store humidified air.
• Some species of fish can breathe air on their own.

How is the digestive system of fish arranged?

Fish grab and hold food with their teeth, which are located in the mouth (as in most vertebrates). Food enters the stomach through the pharynx through the esophagus. There it is processed by gastric juice and the enzymes contained in it. The food then moves into the intestines. Its remains are thrown out through the cloaca ( anus).

What do the inhabitants of the aquatic environment eat? The choice is very wide:

The characterization of the superclass Pisces cannot be complete without a description Life in the water leads fish to a number of problems with osmoregulation. Moreover, these problems are typical for freshwater and marine fish equally. Cartilaginous fish are isosmotic. The concentration of salt in their body is lower than in the environment. Osmotic pressure equalizes due to high content in the blood of fish urea and trimethylamine oxide. low concentration salts the cartilaginous class is maintained due to the work of the rectal gland and the excretion of salts by the kidneys.

Bony fish are not isosmotic. In the course of evolution, they were able to develop a mechanism that traps or removes ions. Biology of the Chordata type helps the fish to bring the salts out into the sea. This is because the fish are losing water. Chloride ions and sodium ions are excreted by the gills, and magnesium and sulfates are excreted by the kidneys.

Freshwater fish have exactly the opposite mechanism. The concentration of salt in the body of such creatures is higher than in the environment. Their osmotic pressure is equalized due to the release a large number urea and the capture of the necessary ions from the water space by the gills.

Superclass Pisces: how does reproduction occur?

Fish have several types of reproduction. Let's consider each of them in more detail.

1. Bisexual reproduction is the most common form. In this case, the two sexes of fish are clearly separated. This is often seen even in outward signs(for example, color). Most often, males have secondary sexual characteristics. They can manifest themselves in the difference in the size of the body of the male and female, the difference in body parts (for example, a longer fin). Males during bisexual reproduction can be monogamous, polygamous, or lead random chaotic relationships (promiscuity).
2. Hermaphroditism - in such fish, the sex can change during life. Protoandria are males at the beginning of life, then after the restructuring of the body they become females. Protogyny is a form of hermaphroditism where all males are transformed females.
3. Gynogenesis is a method of reproduction for fish species represented only by females. It is rarely found in nature.

Fish can reproduce by viviparity, oviparous and ovoviviparous.

Class Bony fish

The superclass Pisces is divided into two classes: Cartilaginous and Bony fishes.

Bony fish - the most numerous group. There are more than 19 thousand species. Their skeleton is bony. In some cases, the skeleton may be cartilaginous, but then it is additionally strengthened. Bony fish have a swim bladder. There are over 40 squads in this class. Let's talk more about the most numerous.

• The Sturgeon order includes ancient bony fish such as sturgeon, beluga, and sterlet. They are distinguished by the presence of a snout and a mouth on the ventral side of the body. The mouth looks like a transverse slit. The basis of the skeleton is cartilage. Sturgeons live only in the Northern Hemisphere.
• Order Herrings are marine schooling fish that feed on plankton. Herring, herring, sardines, anchovies are commercial fish. They lay eggs on the ground or algae.
• Order Salmonformes - freshwater fish that lay their eggs on the bottom. They are found in the Northern Hemisphere. They are valuable commercial fish delicious meat and caviar. The main representatives are salmon, chum salmon, pink salmon, trout, trout.
• Order Cypriniformes are freshwater fish without jaw teeth. They crush their food with their pharyngeal teeth. The order includes commercial fish (roach, bream, tench, ide) and fish artificially bred in water bodies (carp, grass carp, silver carp).
• The lungfish detachment is the oldest detachment. They can breathe with gills and lungs (hollow outgrowths on the wall of the esophagus). They have adapted to life in hot countries and drying up water bodies. Outstanding Representatives order - Australian horntooth and American flake.

cartilaginous fish

The main difference between cartilaginous and bony fish lies in the structure of the skeleton, the absence or presence of gill covers and a swim bladder. The class Cartilaginous fish is represented by the inhabitants of the seas, which have a cartilaginous skeleton throughout their life. Since there is no swim bladder, representatives of this class swim actively so as not to go to the bottom. As in sturgeons, the mouth has the form of a transverse slit, there is a snout.

Cartilaginous fish include only two orders. These are Sharks and Rays. Sharks have a torpedo-shaped body, they are active swimmers and fearsome predators. Their powerful jaws are strewn sharp teeth. At the same time, the largest sharks feed on plankton.

Stingrays have a flattened body with gills near the belly. The fins of the fish are greatly enlarged. Stingrays feed on benthic animals and fish.

Use of fish resources and their protection

Fish is of great importance in human life, being one of the staple foods. About 60 million tons of fish are caught every year around the world. At the same time, herring, cod and mackerel are caught the most.

Recently, the fish catch has been declining markedly. This is due to the deterioration of the environmental situation in the world. Stocks are depleted due to overfishing, destruction of some fish species, pollution of their spawning grounds, poisoning with heavy metal salts. Gradually, humanity is moving from unmanaged fishing to growing fish as a commercial object.

The best successes in raising fish are farms that go back far into history. They carry out full control for the cultivation of products from larvae to marketable products. Fish are bred in artificial ponds for various purposes: feeding, nursery, wintering and so on. There are also special ponds for spawning. They are always small and warm well.

Fish are vertebrates adapted to life in water. Each of you has seen fish and knows that they live in water and die in the air. Fish are also known to lay eggs. But do you know why fish don't drown? Why does he always open his mouth? Why do fish have so many fins? Why is it slippery to the touch? To answer these questions, let us recall the features of life in the aquatic environment. . Find out how the fish could adapt to it.

Body shape and integument of fish. It is more difficult to move in water than in the air, and fish swim easily and quickly. How does it overcome the resistance of water?

Musculoskeletal system and movement of fish. The shape of the forehead, scales, mucus facilitate swimming, but the movements of the fish themselves are due to the work, its musculoskeletal system.

Skeleton and muscles of fish. The basis of the musculoskeletal system of fish is the skeleton (Fig. 32.2). It consists of a skull with a fixed upper jaw and a movable lower jaw, gill arches, gill covers, spine, ribs connected to it and fin bones. The perch has paired fins (pectoral and ventral) and unpaired (caudal, dorsal, anal). The spine consists of a series of vertebrae - separate bones connected by elastic ligaments. Such a spine is both strong and flexible at the same time. The ribs form a frame that protects the internal organs of the fish. Muscles are attached to the skeleton (Fig. 32.3). Structure muscular system perch is the same as that of the lancelet. However, unlike him, fish have muscles associated with fins.

Features of the movement of fish. The perch can move in two ways: by bending its body like a lancelet, and by working its paired fins like oars. There are few muscles on the fins, using them, the perch can swim only slowly. For fast movement it uses the muscles of the torso and tail of the body.

The fins have another important purpose: these organs of movement support the body of the fish in a certain position, preventing it from tipping over to its side. With the help of paired fins, fish make turns. To, for example, turn to the right, it is enough for the fish to make several movements with the left fin, pressing the right one to the body. material from the site

How do fish stay in the water column? For this, according to the law of Archimedes, it is necessary that the density of the body be equal to the density of water. Recall how algae solve this problem: Sargasso have bubbles filled with gas, chlorella and chlamydomonas accumulate fat. And fish equalize the density of the body with the density of water in the same ways. Perch, carp and many other fish have a so-called swim bladder (Fig. 32.3), filled with gases (oxygen, nitrogen, carbon dioxide). The fish can regulate the amount of gas in the swim bladder, and the depth of the fish's immersion also changes accordingly. Sharks do not have a swim bladder, but they store a lot of fat in their livers. But the density of fat is only 10% less than the density of water. In order for the shark not to drown, it must constantly move, and fat reserves must be very large. Therefore, shark liver at 75 % consists of fat and is 20 % from the total body weight of the fish.

On this page, material on the topics:

• Why do fish have a streamlined body shape

• support fish

• Features of the structure of the musculoskeletal system in fish

• Why does a perch dive to a depth and does not move, does not float up and does not sink?

• Supporting and guiding system of the gubui type

Questions about this item:

• Name the devices that facilitate the movement of fish in the water. Which of them are typical for other aquatic animals?

• The internal structure of fish is considered on the example of river perch.

  Musculoskeletal system. The basis of the internal skeleton of the fish (Fig. 117) is the spine and skull.

  Rice. 117. Skeleton of bone fish: A - general form: 1 - jaws; 2 - skull; 3 - gill cover; 4 - shoulder girdle; 5 - pectoral fin skeleton; 6 - skeleton of the ventral fin; 7 - ribs; 8 - fin rays; 9 - vertebrae; B - trunk vertebra; B - tail vertebra: 1 - spinous process; 2 - upper arc; 3 - lateral process; 4 - lower arc

  The spine is made up of dozens of vertebrae similar friend on a friend. Each vertebra has a thickened part - the vertebral body, as well as the upper and lower arches. The upper arcs together form a channel in which lies spinal cord(Fig. 117, B). The arches protect him from injury. Long spinous processes protrude upwards from the arches. In the trunk region, the lower arches (lateral processes) are open. Ribs adjoin 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.

  In the skeleton of the head, a small cranium, or skull, is visible. The bones of the skull protect the brain. The main part of the skeleton of the head 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 up, you can see the gill arches - they are paired: left and right. On the gill arches are the gills. There are few muscles in the head part, 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, reinforced in the thickness of the muscles. The skeleton of the paired fin consists of the skeleton of the girdle and the skeleton of the free limb. 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 is a 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 body of the fish; the muscles that move the tail are especially well developed.

  swim bladder- a special organ peculiar only to bony fish. It is located in the body cavity under the spine. In the course of embryonic development, it arises as a dorsal outgrowth of the intestinal tube (Fig. 118). The swim bladder prevents the fish from drowning under its own weight. It consists of one or two chambers, filled with a mixture of gases close in composition to air. In the so-called open-bladder fish, the volume of gases in the swim bladder can change when they are released and absorbed through the blood vessels of the bladder walls or when air is swallowed. This changes the volume of the fish's body and its specific mass. Thanks to the swim bladder, the mass of the fish's body comes into balance with the buoyancy force acting on the fish at a certain depth.

  

  Rice. 118. Internal structure of bone fish (perch female): 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

  Digestive system begins with a large mouth located at the end of the head and armed with jaws. There is an extensive oral cavity. There are teeth. Behind the oral cavity is the pharyngeal cavity. It shows gill slits separated by intergill septa. They have gills - respiratory organs. This is followed by the esophagus and the voluminous stomach. From the stomach, food enters the intestine. In the stomach and intestines, food is digested under the action of digestive juices: in the stomach, gastric juice, in the intestines - juices secreted by the glands of the intestinal walls and pancreas, as well as bile from the gallbladder and liver. In the intestines, digested food and water are absorbed into the blood. undigested leftovers thrown out through the anus.

  Respiratory system located in the pharynx (Fig. 119, B, C). The gill apparatus is supported 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 the capillaries: the absorption of oxygen from water and the release of carbon dioxide. Water moves between the gill filaments due to the contraction of the muscles of the pharynx and the movement of the gill covers. From the side of the pharynx, bony gill arches carry gill rakers. They protect soft tender gills from clogging with food particles.

  

  Rice. 119. Circulatory and respiratory systems of bony fish: 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 head); 6 - dorsal aorta; 7 - cardinal veins (carry blood to the heart); 8 - abdominal vein; 9 - capillary network internal organs: B - gill arch: 1 - gill rakers; 2 - gill petals; 3 - gill plate; B - breathing pattern: 1 - direction of water flow; 2 - gills; 3 - gill covers

  Circulatory system fish closed (Fig. 119, A). Blood continuously flows through the vessels due to the contraction of a two-chambered heart, consisting of an atrium and a ventricle. Passes through the heart deoxygenated blood containing carbon dioxide. When the ventricle contracts, it sends blood forward into large vessel - abdominal aorta. In the region of the gills, it splits into four pairs of afferent branchial arteries. They branch into capillaries forward in the gill filaments. Here, the blood is released from carbon dioxide, enriched with oxygen (becomes arterial), and through the efferent branchial arteries is sent 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, blood gives off oxygen, is saturated with carbon dioxide (becomes venous) and enters the heart through the veins.

  Nervous system. The central nervous system (CNS) consists of the brain and spinal cord (Fig. 120, A). The brain has five sections: anterior, diencephalon, midbrain, cerebellum and medulla oblongata (Fig. 120, B).

  

  Rice. 120. Nervous system of bone fish: A - general scheme: 1 - cranial nerves; 2 - brain; 3 - spinal cord; four - spinal nerves; B - scheme 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 that connect the central nervous system with organs. The cranial nerves originate from the brain. They provide the work of the sense organs and some internal organs. Spinal nerves branch off from the spinal cord. They regulate the coordinated work of the muscles of the body, organs of movement, internal organs. The nervous system coordinates the activity of the whole organism, the adequate reactions of animals to the influence of the external environment.

  excretory organs represented by the kidneys located along the spine, ureters and bladder(see fig. 118). Through these organs, excess salts, water and waste products harmful to the body are removed from the body of the fish.

  Urine enters the bladder through the ureters and is expelled from it.

  Lab #7

  Topic. The internal structure of a fish.

  Target. Explore Features internal structure fish and its complication in comparison with non-cranial animals.

  Equipment: tweezers, bath, ready-made wet fish preparation (or opened fresh fish).

  Progress

  1. Consider the location of the internal organs in the body of a fish.
  2. Find and examine the gills. Determine their location. Determine which organ system they belong to. How do fish breathe?
  3. Find the stomach, intestines, liver.
  4. Find on wet preparation heart. Establish its location in the body cavity. What organs belong to the circulatory system? Why is this circulatory system called closed?
  5. Decide if you are considering a female or male. Establish the location of the testes (ovaries) in the body cavity.
  6. Determine the location of the kidneys in the body cavity. Indicate to which organ system the examined organs belong. How is the removal harmful products life from the body of a fish?
  7. Make a conclusion.

  Compared to lancelets, fish are more highly organized animals. Their notochord is replaced by a spine; gills have a complex structure; the heart is muscular, two-chambered; The excretory organs are the kidneys, ureters and bladder. The central nervous system (neural tube) is divided into the brain (five sections) and the spinal cord.

  Lesson learned exercises

  1. Name the main parts of the fish skeleton. What function do they perform?
  2. What organs make up the musculoskeletal, respiratory, circulatory, central nervous system fish?
  3. List character traits internal structure of fish.
  4. Explain the importance of the swim bladder in the life of bony fish.

  The musculoskeletal system of fish system of organs and tissues of fish, which allows them to move and adjust their position in the environment. Thanks to evolutionary modifications, parts of the musculoskeletal system are adapted to perform other specialized functions as well. The skeleton of bony fish is divided into axial skeleton, skull, skeleton of unpaired fins, skeleton of paired fins and their belts. The skeleton consists of cartilaginous (chondral) and integumentary, or false bones. The first formed as a result of cartilage replacement bone tissue. The integumentary bones form in the corium and sink under the skin.

  The structure of the skull of fish

  Unlike terrestrial vertebrates, which have a skull with large quantity fused bones, the skull of fish contains more than 40 bone elements, which can move independently. This allows for the extension of the jaws, the jaw cover to the sides, the lowering of the gill apparatus and the floor of the oral cavity.

  The skull is predominantly bony, formed by both superimposed and chondral bones. Chondral ossification form the back of the cranium, its sides and partly the bottom. False bones cover the primary cranium, forming a cover and partially sides.

  The skull of bony fish, like all vertebrates, is divided into cerebral (axial) and visceral sections. The brain consists of several sections: occipital, auditory, orbital, olfactory. The roof, partly the sides and the bottom of the skull are odd bones - nasal, frontal, parietal. The bottom of the skull is formed by a parasphenoid (parasphenoideum) and a plowshare (vomer). The visceral skull consists of the jaw, hyoid, and 5 gill arches, as well as the gill covers.

  The skull of bony fish is characterized by hyostyle: the attachment of the jaw arch and secondary jaws With cerebral skull through the upper element of the hyoid arch - pendants or hyomandibular.

  Movable elements attach to the more rigidly articulated neurocranium surrounding the brain. The neurocranium of bony fish is evolutionarily formed from the cartilaginous skull of cartilaginous fish, to which skin bony plates adhere.

  Jaws in the classes of bony and cartilaginous fish are evolutionarily formed from the third pair of gill arches (as evidenced by the rudiments of the first two pairs of arches in sharks - the so-called labial cartilages).

  In bony fish, the jaws bear the main groups of teeth on the premaxilla (premaxilla) and maxillary bones (maxilla) (upper jaw), on the dentale and articulare (lower jaw), and also, in many species, on the plowshare (vomer).

  Several specialized groups of bones form the floor of the mouth and combine the jaws with other elements of the skull. The most rostral (in front) is the geoid arc, plays important role when changing the volume of the oral cavity. Then the gill arches follow, they carry gill respiratory structures, and the so-called pharyngeal jaws are located most caudally (behind) and can also bear teeth.

  During muscle nutrition, lower the complex mandible, displace this complex so that the jaws move forward. In this case, a suction force is generated in the oral cavity due to the lowering of the bottom of the mouth. The gill covers cover the gills. This combination of movements leads to the absorption of water and the dragging of food into the mouth.

  Axial skeleton, skeleton of paired and unpaired fins

  The spine of fish consists of separate, not fused in one section, vertebrae. The vertebrae of fish are amphitceles (i.e., both of their end surfaces are concave), there are cartilaginous layers between the vertebrae. The notochord is greatly reduced, widened between the vertebral bodies and, in a strongly narrowed form, passes through the canal in the vertebral bodies. The neural arch above the vertebral body protects the spinal cord and passes through it. From the vertebrae located in the body, lateral processes extend to the sides, to which the ribs are attached. There are no lateral processes on the vertebrae in the caudal region of the spine, but apart from neural arch there is a vascular arch, attached to the vertebra from below and protects the large blood vessel- abdominal aorta. Pointed processes extend vertically up and down from the nerve and vascular arches.

  The driving force when swimming fish is produced by fins: paired (pectoral and ventral) and odd - dorsal, anal, caudal. Moreover, in ray-finned fish, the fins consist of bony (in some primitive rows - cartilaginous) rays, united by a swimming blade. Attached to the base of the arms, the muscles can turn or fold the swimmer, or change its orientation, or generate the swimmer's undulating motion. The caudal fin, which in most fish is the main generator of movement, is supported by a set of special flattened bones (urostyle, etc.) and associated muscles in addition to the lateral muscles of the trunk. According to the ratio of the sizes of the upper and lower lobe, the caudal fin can be homocercal (when both lobes are of equal size, this is typical for most ray-finned fish) or heterocercal (when one lobe, of course the upper one, is larger than the other; typical for sharks and rays, with ray-finned fish - for sturgeon-like, in such representatives ray-finned as swordtails, the caudal fin is heterocercal with a larger lower lobe).

  musculature

  The somatic muscles are striated.

  A membrane extends to the right and left of the spine from connective tissue, is called the horizontal septum and divides the muscles of the body of the fish into dorsal (upper) and ventral (lower) parts, called myomeres.

  Swimming of fish is carried out thanks to the contraction of muscles connected by tendons to the spine. Myomers in the body of fish have the structure of cones nested in each other and separated by connective tissue partitions (myosepts). The contraction of the myomere through the tendons is transmitted to the spine, prompting it to wave-like movement - along the entire length of the body, or only in the tail section.

  In general, the musculature of fish is represented by two types of muscles. "Slow" muscles are used for calm swimming. They are slowly oxidized and rich in myoglobin, which gives them a red color. Metabolism occurs through oxygenation nutrients. Due to the constant oxygen saturation, such red muscles can not get tired for a long time, and therefore they are used for long monotonous swimming. Unlike red, "fast" white muscles with glycolytic rather than oxygenated metabolism are capable of rapid sudden contraction. They are used in fast sudden jerks, while they can generate more power beyond the red muscles, but quickly get tired.

  Part of the somatic musculature turned into other muscle groups: ophthalmic, supraorbital and juvenile, maxillary, and pectoral fin muscles.

  Also, in many fish, muscles can perform some other functions besides movement. In some species, they function as thermostats, or "heating batteries". In tunas (family Scombridae), due to the activity of the musculature, the temperature of the brain is maintained at high level than in other parts of the body when tunas prey on squid in deep cold waters.

  The electrical current generated by muscle contraction is used by the elephantfish as a communication signal; in electric rays, electrical impulses generated by modified muscles are used to defeat other animals. The modification of muscle cells to perform the function of an electrical battery has evolved independently and repeatedly in different taxa: eye muscles in starfish (family Uranoscopidae), chewing muscles (electric rays) or axial muscles (electric eels).

  Visceral muscles surrounding digestive tract, is represented by smooth muscle.