What is the structural feature of all bony fish? Bone. Functions of bone tissue

Fish are cold-blooded vertebrates that belong to the multicellular subkingdom, the phylum Chordata. They managed to adapt to a wide variety of environmental conditions. They live both in freshwater and saltwater reservoirs, up to 10 thousand meters deep, and in drying up river beds with water from 2 to 50 degrees, etc. Their body temperature is almost equal to the temperature of the water in which they live, and does not exceed it by more than 0.5 - 1 C (tuna fish species can have a much larger difference of up to 10 C). Thus, the environment affects not only the speed of digestion, but also the shape of the body, which is divided into the following types:

• fusiform ( sharks);
• flattened in bottom inhabitants ( stingrays, flounders);
• streamlined, torpedo-shaped in individuals that spend most of their lives in the water column ( mullet, tuna);
• sagittal ( pike);
• spherical ( bodies).

Natural selection left the fish most adapted to one or another environment, providing for their survival and reproduction, which ensured the continuation and prosperity of the family from generation to generation.

Despite the external and internal differences formed by the habitat, the structure of the fish has General characteristics. Like all vertebrates, they have a skeleton with muscles, skin, an excretory system, reproductive, sensory and respiratory organs, a digestive, nervous and circulatory system.

Skeleton and musculature

Most fish have a bony or cartilaginous skeleton, but there are also individuals with a cartilaginous skeleton. For example, shark, stingray. Based on this, a logical question follows: How does the structure of bony fish differ from cartilaginous fish?

Structure of bony fish

The structural features of bony fish include the presence of a spine, a brain skull, a skeleton of the limbs and their girdles. The basis of the spine is a considerable number of individual bones, the so-called vertebrae. They have a very strong connection, but movable, because Between them there is a cartilaginous layer. The spine is divided into the caudal and, of course, the trunk. The ribs of fish articulate with the transverse processes of the vertebral bodies.

Muscles are naturally attached to the bones of the skeleton, which form the musculature. The strongest muscles in fish are located in the tail, for obvious reasons, and on the dorsal side of the body. Thanks to muscle contraction, the fish reproduces movement.

The structure of cartilaginous fish

The cartilaginous skeleton is impregnated with calcium salts, which is why it retains its strength. A particular feature of the structure of cartilaginous fish is that their skull is fused with the jaws (hence the name whole-headed), or creates one or two joints with them (elasmobranchs). The mouth with teeth covered with enamel is located on the ventral side. In front of the mouth there is a pair of nostrils. The notochord remains throughout life, but gradually decreases in size.

Fins

The external structure of the fish differs in the fins. Some consist of soft (branchy), while others consist of hard (prickly, may have the appearance of a jagged saw or powerful thorns) rays. The fins are connected by a membrane or free. They are divided into two groups - paired (abdominal and thoracic) and unpaired (anal, dorsal, caudal and adipose, which not all species have). The bony rays of the fins are combined with the bones of the limb girdles.

For many bony fish A formula is compiled based on the nature and presence of rays in the fins. It is widely used in identifying and describing fish species. In the formula, the Latin abbreviation for the fin designation is given:

A– (from the Latin language pinna analis) anal fin.
D1, D2 – (pinna dorsalis) dorsal fins. Roman numerals indicate prickly ones, and Arabic numerals indicate soft ones.
P – (pinna pectoralis) pectoral fin.

V – (pinna ventralis) ventral fin.

In cartilaginous fish there are paired pectoral, dorsal and pelvic fins, as well as a caudal fin.

When a fish swims, the driving force comes from the tail and caudal fin. They are the ones who push the fish’s body forward with a powerful blow. The tail swimmer is supported by special flattened bones (for example, urostyle, which is translated from Greek as stick, support, etc.). The anal and dorsal fins help the fish maintain balance. The rudder is the pectoral fins, which move the fish’s body during slow swimming, and together with the caudal and ventral fins, it helps to maintain balance when the fish is not moving.

In addition, fins can perform completely different functions. For example, in viviparous individuals, the anal, modified fin became the mating organ. Gouramis have filiform pelvic fins in the form of tentacles. There are species of fish with sufficiently developed pectoral fins that allow them to jump out of the water. Other individuals that burrow into the ground often have no fins at all.

The tail fins have the following types:

• Truncated;
• Round;
• Split;
• Lyre-shaped.

The swim bladder allows the fish to remain at one depth or another, but here without any muscular effort. This important formation begins as a growth on the dorsal edge of the intestine. Only bottom fish and good swimmers, who for the most part belong specifically to cartilaginous fish. Due to the absence of this outgrowth, they are forced to constantly be on the move so as not to drown.

Skin covering

The skin of a fish consists of a multilayered epidermis (or epithelium) and a connective tissue dermis located underneath. The epithelial layer contains numerous glands that secrete mucus. This mucus performs a number of functions - it reduces friction with the water when the fish swims, protects the fish's body from external influences and disinfects superficial wounds. The epithelial layer also contains pigment cells, which are responsible for the color of the fish’s body. In some fish, coloration varies depending on mood and environmental conditions.

In most fish, the body is covered with protective formations - scales, which are cartilaginous or bone formations consisting of 50% organic substances and 50% inorganic substances, such as calcium phosphate, sodium, magnesium phosphate and calcium carbonate. Microminerals are also present in the scales.

The habitat and features of the external structure of fish affect the variety of shapes, sizes and number of scales in different species. Some may have virtually no scales at all. Others have large scales. For example, in some carp they can reach a couple of centimeters. However, in general, the body size of a fish is directly proportional to its scales and is determined by the linear equation:

Ln=(Vn/V)

In which:
L– length of the fish;
Ln– this is the estimated length of the fish at age;
V– length of scales from center to edge;
Vn– distance from the center of the cover (scales) to the annual ring (aged).

Of course, the environment and lifestyle directly influence the structure of the scales. So, for example, swimmer fish, which spend most of their lives in motion, have developed, strong scales, which help reduce body friction with the water and also impart speed.

Specialists stand out three types of scales:

• bony (divided into cycloid - smooth, rounded and ctenoid, which has small spines along the posterior edge);
• ganoid,
• placoid.

Bone scale It is characterized by the presence of only bone substance in its composition. The following fish species have it: herring, carp, and perch.

Ganoid scale It has a diamond shape and is connected to each other using special joints, which is why it looks like a dense shell. In the upper part, strength is achieved due to ganoin, and in the lower part - bone substance. Such scales are typical for lobe-finned (all over the body) and sturgeon (only on the tail) fish.

Placoid scales found in fossil fish. It is the most ancient and, like the ganoid, is a diamond shape, but with a spike that protrudes outward. IN chemical composition the scales have dentin, and the spine is covered with special enamel - vitrodentin. A special feature is that this type of scale is characterized by a cavity, which is filled with loose connective tissue with nerve fibers and even blood vessels. Modified placoid scales are also possible, for example, the spines of stingrays. In addition to stingrays, sharks also have placoid scales. It is typical for cartilaginous fish.

The scales on the body are arranged in a row; the number does not change with age, and therefore sometimes serves as a species characteristic. For example, the lateral line of pike has 111-148 scales, and crucian carp - 32-36.

Excretory system

On both sides of the spine, above the fish's swim bladder, there are ribbon-shaped kidneys. As you know, this is a paired organ. There are three sections in the kidney: anterior (head kidney), middle and posterior.

Venous blood enters this organ through the portal veins of the kidneys, and arterial blood through the renal arteries.

The morphophysiological element is the tortuous renal urinary canal, in which one end increases in the Malpighian body, and the other goes to the ureter. Products of nitrogenous breakdown, namely urea, enter the lumen of the tubules and are secreted by glandular cells. There, the reabsorption of microelements and all kinds of vitamins from the filtrate of Malpighian corpuscles (a glomerulus of arterial capillaries, which is covered by the enlarged walls of the tubule and creates Bowman’s capsule), sugars and, of course, water occurs.

The filtered blood flows back into the kidney's vascular system, the renal vein. And urea and metabolic products exit through the tubule into the ureter, which in turn pours into the bladder or, in other words, the urinary sinus, and then the urine comes out. For a huge number of fish, the final breakdown product is ammonia (NH3).

Marine species drink water and excrete excess salts and ammonia through their kidneys and gills. Freshwater fish species do not drink water; it continuously enters the body and is excreted through the urogenital opening in males and through the anus in females.

Reproductive organs

The sex glands, or gonads, are represented in males by paired milky-white testes, in females - by sac-like ovaries, the ducts of which open outward through the urogenital opening or the genital papilla behind the anus. Fertilization in bony fishes, as a rule, external, but in some species the anal fins of males have been transformed into a copulatory organ - gonopodium, intended for internal fertilization.

The female lays eggs, which the male fertilizes with seminal fluid. After the incubation period, larvae hatch from the eggs, which initially feed on the yolk sac.

On the structural features of cartilaginous fish can be considered internal fertilization. Most of them have a cloaca. Males (males) have several pelvic fins, which form the copulatory organ. By nature, cartilaginous fish are egg-laying or viviparous.

Sense organs

Important sense organs that influence the behavior of fish when searching for and eating food, and also determine temperature and chemical changes in water, are: vision, ear, smell, taste and lateral line.

Smell and taste

A pair of small nasal pits, which are covered with olfactory epithelium, are the organ of smell. With it, fish sense chemical irritants from substances dissolved in water. Nocturnal inhabitants, such as carp, bream, and eel, have a better developed sense of smell.

Not everyone knows that fish have a well-developed taste organ. They determine salty, sweet, sour and bitter tastes. Taste buds are located along the edges of the jaws, in the oral cavity and on the antennae. Fish that do not have antennae have a poorly developed taste.

Vision

The most important organ of a fish is vision. The structure and capabilities of a fish’s eye depend on the species and directly on its habitat. For example, the ability to see in eel and catfish is secondary in comparison with trout, pike, grayling and other fish that use vision when hunting. However, one way or another, the eyes of fish are adapted to life under water.

The lens of a fish's eye, compared to a human's, is elastic (not able to change shape) and quite hard. In an unexcited state, it is located near the cornea and allows the fish to see at a distance of up to 5 meters in a straight line. When viewing at a greater distance, the lens moves away from the cornea and, with the assistance of the ligaments, approaches the retina. This allows the fish to see up to 15 meters in the water, which is quite shocking. By the size of the eye, which correlates with the head of the fish, you can determine visual acuity and ability to see the world.

The back part of the retina, thanks to special cells - cones (allow you to see daylight) and rods (perceive twilight), recognizes color. Pisces are able to distinguish shades, approximately in the same range as humans. However, in comparison with humans, they also see the short-wavelength region of the spectrum, which the human eye does not perceive. Fish are also more sensitive to warm colors: yellow, red and orange.

What structural features distinguish amphibians from fish?

In the diagram you can see that each shade of the solar spectrum is characterized by a certain wavelength, while the vision of fish and humans is not equally sensitive to light with different wavelengths, that is, to a variety of colors. The relative susceptibility to light of different wavelengths at low light intensity is also shown. At high levels, the sensitivity shifts towards longer wavelengths. Quantity daylight penetrating under the surface of the water, of course, depends on the angle of its incidence on the surface of the water, as well as on how strongly the surface of the water fluctuates, i.e. is agitated. Light rays are partially absorbed by water and some of them are scattered by solid microscopic particles that are suspended in water. The rays that penetrate the entire layer of water and reach the bottom are partially absorbed and partially reflected.

There are a number of factors that affect vision in water, which is why there are a number of differences with atmospheric visibility:
1. The individual does not see objects that are under the fish clearly, but exactly in the place where they actually are.
2. The individual sees objects that are in front or above the fish most clearly.
3. Due to the fact that the fish's eyes are located on the sides of its head, it can only see in a small space behind, side and in front.
4. The fish sees a light cone above itself, with the help of which it observes, for example, live or dry food. In this case, being in a pond or river, the individual will see the object on the shore distorted.
5. Light rays are not refracted when passing from air to water perpendicular to the surface of the water. In connection with this, when viewed from above, a person sees the fish exactly where it actually is. The fish sees objects above the water as if looking through a round window. Objects that lie in space are limited by the fish's field of view. They may appear at the edges of this window, while items directly above the fish are placed in the middle.
6. Light rays travel faster in air than in water due to its dense medium. That is why a ray of light, passing at any angle from the first medium to the second, is refracted.

The visual perception of fish is also influenced by other factors, such as the purity and speed of water flow, and the line of refraction of light.

Side line

Of particular importance for fish is the lateral line canal system, which communicates with external environment holes. The lateral line stretches along the fish’s body and is capable of perceiving water vibrations, the presence of objects in the fish’s path, the speed and direction of currents. Even a blind fish is able to navigate space quite well.

Ear

The inner ear of fish consists of three semicircular canals, which are actually the organ of balance, and a sac that perceives sound vibrations.

Electric organs

Some species of cartilaginous fish have an electrical organ. It is intended for protection, orientation and signaling in space, as well as for attack. This paired organ is located on the sides of the body, or near the eyes, and consists of electric plates (modified cells) arranged in columns that generate electric current. In each such column, the plates are connected in series, but the columns are connected in parallel. The number of records in general amounts to hundreds of thousands, and sometimes millions. The discharge frequency depends on the purpose and is up to hundreds of hertz, and the voltage is up to 1200V. By the way, electrical discharges from fish such as eels and stingrays are dangerous to human life.

Respiratory system

Most fish breathe oxygen dissolved in water using gills. The gill openings are located in the anterior section of the digestive tube. The respiratory process is carried out through movements of the gill covers and mouth opening, due to which water washes the gill filaments located on the gill arches. Each gill filament contains capillaries into which the gill artery, which carries venous blood from the heart, breaks up. Having enriched with oxygen and lost carbon dioxide, the blood from the capillaries is sent to the efferent gill arteries, which merge into the dorsal aorta, and through the arteries extending from it, the oxidized blood spreads to all organs and tissues of the fish. Oxygen can also be absorbed by the intestinal mucosa, which is why some fish species often swallow air from the surface of the water.

Some individuals have additional respiratory organs in addition to gills. So, for example, in fish of the Anabantidae family, which includes many popular representatives of the aquarium ichthyofauna ( macropods, gourami, lalius), have a special organ - the gill labyrinth. Thanks to it, fish are able to absorb oxygen from the air. Moreover, if this family for some reason cannot rise to the surface of the water for several hours, then it dies.

The source of oxygen in aquarium water, as in natural reservoirs, is natural gas exchange with the surrounding air. Aeration of water using microcompressors and pumps improves this gas exchange in an artificial environment. IN natural conditions waves, rapids, and riffles come to the rescue. Also, a large amount of oxygen is supplied by plants during the daytime during the process of photosynthesis. At night, they absorb it.

The amount of oxygen required for the life of fish can vary. It depends on the water temperature, the size and type of fish, as well as the degree of their activity.

It is no secret that the solubility of gases decreases as the temperature of the liquid increases. The oxygen content in water that comes into contact with atmospheric air is usually less than the solubility limit:
0.7 milliliters per 100 grams of water at 15 C;
0.63 milliliters at 20 C;
0.58 milliliters at 25 C;

This ratio is sufficient for the inhabitants of the aquarium. Moreover, from 0.55 milliliters to 0.7 milliliters per 100 grams of water is optimal and beneficial for most fish species.

Digestive system

The digestive tract of fish is very diverse in shape, structure, length and depends on the type (predators or herbivores), species and habitat of the individuals. However, general points can be noted.

The digestive system includes: the mouth and oral cavity, pharynx, esophagus, stomach, intestines (large, small and rectum, ending with the anus). Selected species fish have a cloaca in front of the anus, i.e. the cavity in which the rectum will appear, as well as the ducts of the reproductive system and urinary system.

The mouth opening of a fish is necessary for receiving, sometimes chewing and swallowing food. There are no salivary glands, but the taste buds, which were written about earlier, are present. Some species are equipped with a tongue and teeth. Teeth can be located not only on the jaws, but also on the palatal bones, pharynx and even tongue. Usually they do not have roots and are replaced by new ones over time. They serve to capture and hold food, and also perform a protective function.

Herbivores mostly do not have teeth.

From the oral cavity, food passes through the esophagus into the stomach, where it is processed using gastric juice, the main components of which are hydrochloric acid and pepsin. However, not all individuals have a stomach; these include: many gobies, cyprinids, monkfish, etc. Predators mainly have this organ.

Moreover, in different species of fish, the stomach may differ in structure, size and even shape: oval, tubes, letter V, etc.

In some herbivorous species, symbiotic protozoa and bacteria take part in the digestion process.

The final processing of food is carried out in the intestines with the help of secretions secreted by the liver and pancreas. It starts in the small intestine. The pancreatic ducts and the bile duct flow into it, which deliver enzymes and bile to the intestine, which break down proteins into amino acids, fats into fatty acids and glycerol, and polysaccharides into sugars.

In addition to the process of breaking down substances in the intestines, due to the folded structure of the walls, they are absorbed into the blood, which flows intensively in the posterior region.

The intestine ends with the anus, which is usually located at the end of the body, immediately in front of the genital and urinary openings.

The digestive process in fish also involves glands: the gallbladder, pancreas, liver and ducts.
The nervous system of fish is much simpler than that of higher vertebrates. It includes the central and associated autonomic (sympathetic) and peripheral nervous systems.

The CNS (Central Nervous System) includes the brain and spinal cord.

The nerves that branch from the brain and spinal cord to the organs are called the peripheral nervous system.

The autonomic nervous system is the nerves and ganglia that innervate the muscles of the blood vessels of the heart and internal organs. The ganglia are located along the spine and are connected to the internal organs and spinal nerves. Intertwined, the ganglia unite the central nervous system with the autonomic nervous system. These systems are interchangeable and independent of each other.

The central nervous system is located along the entire body: the part of it that is located in a special spinal canal formed by the upper arches of the spine forms the spinal cord, and the spacious anterior lobe, surrounded by a bone or cartilaginous skull, forms the brain.

The brain has five sections: the cerebellum, midbrain, medulla oblongata, diencephalon and forebrain. The gray matter of the forebrain, in the form of striped bodies, is located at the base and in the olfactory lobes. It analyzes the information that comes from the olfactory organs. In addition, the forebrain controls behavior (stimulates and participates in the vital processes of fish: spawning, school formation, territory defense and aggression) and movement.

The optic nerves branch off from the diencephalon, so it is responsible for the vision of fish. The pituitary gland (pituitary gland) is adjacent to its lower side, and the epiphysis (pineal gland) is adjacent to the upper part. Pineal and pituitary glands internal secretion. Also, the diencephalon is involved in the coordination of movement and the functioning of other senses.

In fish, the cerebellum and midbrain are best developed.

Midbrain includes the largest volume. It has the shape of two hemispheres. Each lobe is a primary visual center that processes signals from the organs of taste, vision, and perception. There is also a connection with the spinal cord and cerebellum.

Cerebellum has the appearance of a small tubercle, which is adjacent to the medulla oblongata on top. However, it is also found in large sizes, for example, in catfish and mormius.

The cerebellum is primarily responsible for proper coordination of movements and maintaining balance, as well as muscle work. It is connected to the lateral line receptors and synchronizes the work of other parts of the brain.

Medulla smoothly passes into the dorsal and consists of white-gray matter. It regulates and controls the functioning of the spinal cord and autonomic nervous system. Also important for the circulatory, musculoskeletal, respiratory and other systems of fish. If this part of the brain is damaged, the fish immediately dies.

Like many other systems and organs, the nervous system has a number of differences depending on the type of fish. For example, individuals may have different levels of formation of the lobes of the brain.

Structural features of representatives of the class cartilaginous fish (rays and sharks) include: olfactory lobes and developed forebrain. Bottom-dwelling and sedentary individuals have a small cerebellum and well-developed medulla oblongata and forebrain, because the sense of smell plays an important role in their life. In fast-swimming fish, the cerebellum is well developed, which is responsible for the coordination of movement, and the midbrain is responsible for the visual lobes. But in deep-sea individuals, the visual lobes of the brain are weak.

The continuation of the medulla oblongata is the spinal cord. Its peculiarity is that it quickly regenerates and recovers when damaged. There is gray matter inside, white matter outside.

The spinal cord serves as a conductor and receiver of reflex signals. Spinal nerves branch from it, which innervate the surface of the body, the muscles of the trunk, through the internal organs and ganglia.

In bony fish The spinal cord contains the urohypophysis. Its cells produce a hormone that takes part in water metabolism.

The most famous manifestation of the nervous system of fish is the reflex. For example, if fish are fed for a long time in the same place, they will preferentially swim there. In addition, fish can develop reflexes to light, vibration and temperature of water, smell and taste, as well as shape.

It follows from this that, if desired, an aquarium fish can be trained and develop certain behavioral reactions in it.

Circulatory system

The structure of the heart of fish also has its differences in comparison with amphibians. It is very small and weak. Usually its mass does not exceed 0.3-2.5%, and the average value is 1% of body weight, while in mammals it is about 4.6%, in birds generally 10-16%.

In addition, fish have low blood pressure and low frequency heart contractions: from 17 to 30 beats per minute. However, at low temperatures it can decrease to 1-2. Fish that survive freezing into ice during the winter season do not have a heart pulsation at all during this period.

Another difference in circulatory system mammals and fish is that the latter have a small amount of blood. This is explained by the horizontal position of the life activity of fish, as well as the habitat where the force gravity has a much smaller effect on the body than in the air.

The heart of fish is two-chambered and consists of one atrium and ventricle, conus arteriosus and sinus venosus. Fish have only one circle of blood circulation, except for lobe-finned fish and lungfish. Blood moves in a vicious circle.

From the ventricle comes the abdominal aorta, from which four pairs of delivery branchial arteries branch. These arteries in turn break up into capillaries, in which the blood is enriched with oxygen. Oxidized blood flows through the efferent branchial arteries into the roots of the dorsal aorta, which is divided into the internal and external carotid arteries, which merge into the dorsal aorta, and from it into the atrium. Thus, all body tissues are saturated with maximally oxygenated blood.

Erythrocytes (red blood cells) of fish contain hemoglobin. They bind carbon dioxide in tissues and organs, and oxygen in the gills. Depending on the type of fish, the capacity of hemoglobin in the blood may vary. For example, fast-swimming individuals living in water bodies with good content oxygen, have cells with excellent oxygen binding capacity. Unlike red blood cells in mammals, in fish they have a nucleus.

If arterial blood is enriched with oxygen (O), it is colored bright scarlet. Venous blood, which is saturated with carbon dioxide (CO2) and poor in oxygen, is dark cherry.

It is noteworthy that the fish body has the ability to form hematopoiesis. Most organs, such as the spleen, kidneys, gill apparatus, intestinal mucosa, vascular endothelium and the epithelial layer of the heart, lymphoid organ, can create blood.

At the moment, 14 fish blood group systems have been identified.

Thanks to the fact that every being is endowed, we all receive what we cannot live without - oxygen. In all land animals and humans, these organs are called lungs, which absorb the maximum amount of oxygen from the air. fish, on the other hand, consists of gills that draw oxygen into the body from the water, where there is much less of it than in the air. It is because of this that the body structure of this biological species is so different from all spinal terrestrial creatures. Well, let's look at all the structural features of fish, their respiratory system and other vital organs.

Briefly about fish

First, let's try to figure out what kind of creatures these are, how and how they live, and what kind of relationship they have with humans. Therefore, now we are starting our biology lesson, the topic “Sea Fishes”. This is a superclass of vertebrates that live exclusively in the aquatic environment. A characteristic feature is that all fish are jawed and also have gills. It is worth noting that these indicators are typical for everyone, regardless of size and weight. In human life, this subclass plays an economically important role, since most of its representatives are consumed as food.

It is also believed that fish were around at the dawn of evolution. It was these creatures that could live under water, but did not yet have jaws, that were once the only inhabitants of the Earth. Since then, the species has evolved, some of them turned into animals, some remained under water. That's the whole biology lesson. The topic "Sea fish. A brief excursion into history" is considered. The science that studies marine fish is called ichthyology. Let's now move on to studying these creatures from a more professional point of view.

General structure of fish

Generally speaking, we can say that the body of each fish is divided into three parts - head, body and tail. The head ends in the area of ​​the gills (at their beginning or end - depending on the superclass). The body ends at the line of the anus in all representatives of this class of marine inhabitants. The tail is the simplest part of the body, which consists of a rod and a fin.

Body shape strictly depends on living conditions. Fish that lives in the middle water column (salmon, shark) have a torpedo-shaped figure, less often - arrow-shaped. Those that float above the very bottom have a flattened shape. These include foxes and other fish that are forced to swim among plants or stones. They acquire more maneuverable shapes, which have much in common with snakes. For example, the eel has a highly elongated body.

The business card of a fish is its fins

Without fins it is impossible to imagine the structure of a fish. Pictures that are presented even in children's books certainly show us this part of the body of sea inhabitants. What are they?

So, fins are paired and unpaired. The paired ones include the pectoral and abdominal ones, which are symmetrical and move synchronously. Unpaired ones are presented in the form of a tail, dorsal fins (from one to three), as well as anal and adipose fins, which are located immediately behind the dorsal fin. The fins themselves consist of hard and soft rays. It is based on the number of these rays that the fin formula is calculated, which is used to determine a specific type of fish. The location of the fin is determined by Latin letters (A - anal, P - pectoral, V - ventral). Next, the number of hard rays is indicated in Roman numerals, and soft rays in Arabic numerals.

Fish classification

Today, all fish can be roughly divided into two categories - cartilaginous and bony. The first group includes sea inhabitants whose skeleton consists of cartilage of various sizes. This does not mean that such a creature is soft and incapable of movement. In many representatives of the superclass, the cartilage hardens and becomes almost bone-like in density. The second category is bony fish. Biology as a science claims that this superclass was the starting point of evolution. It once contained a long-extinct lobe-finned fish, from which all land mammals may have descended. Next, we will take a closer look at the body structure of fish of each of these species.

Cartilaginous

In principle, the structure is not something complex or unusual. This is an ordinary skeleton, which consists of very hard and durable cartilage. Each connection is impregnated with calcium salts, thanks to which strength appears in the cartilage. The notochord retains its shape throughout life, while it is partially reduced. The skull is connected to the jaws, as a result of which the fish skeleton has an integral structure. Fins are also attached to it - caudal, paired abdominal and pectoral. The jaws are located on the ventral side of the skeleton, and above them are two nostrils. The cartilaginous skeleton and muscular corset of such fish are covered on the outside with dense scales, which are called placoid. It consists of dentin, which is similar in composition to ordinary teeth in all land mammals.

How do cartilage breathe?

The respiratory system of cartilaginous animals is represented primarily by gill slits. There are from 5 to 7 pairs on the body. Oxygen is distributed to the internal organs thanks to a spiral valve that stretches along the entire body of the fish. A characteristic feature of all cartilaginous animals is that they lack a swim bladder. That is why they are forced to constantly be on the move so as not to sink. It is also important to note that the body of cartilaginous fish, which a priori live in salty waters, contains a minimal amount of this very salt. Scientists believe that this is due to the fact that this superclass has a lot of urea in the blood, which consists mainly of nitrogen.

Bone

Now let’s look at what the skeleton of a fish that belongs to the bony superclass looks like, and also find out what else is characteristic of representatives of this category.

So, the skeleton is presented in the form of a head, a torso (they exist separately, unlike the previous case), as well as paired and unpaired limbs. The cranium is divided into two sections - the brain and the visceral. The second includes the maxillary and hyoid arches, which are the main components of the jaw apparatus. Also in the skeleton of bony fish there are gill arches, which are designed to hold the gill apparatus. As for the muscles of this type of fish, they all have a segmental structure, and the most developed of them are the jaw, fin and gill muscles.

Respiratory apparatus of bony sea creatures

It has probably already become clear to everyone that the respiratory system of fish of the bony superclass mainly consists of gills. They are located on the gill arches. Also an integral part of such fish are gill slits. They are covered with a lid of the same name, which is designed to allow the fish to breathe even in an immobilized state (unlike cartilaginous ones). Some representatives of the bone superclass can breathe through the skin. But those that live directly below the surface of the water, and at the same time never sink deeply; on the contrary, they capture air with their gills from the atmosphere, and not from the aquatic environment.

Structure of the gills

Gills are a unique organ that was previously characteristic of all primordial aquatic creatures that lived on Earth. In it, the process of gas exchange occurs between the hydroenvironment and the organism in which they function. The gills of fish of our time are not much different from those gills that were characteristic of the earlier inhabitants of our planet.

As a rule, they are presented in the form of two identical plates, which are penetrated by a very dense network of blood vessels. An integral part of the gills is the coelomic fluid. It is she who carries out the process of gas exchange between the aquatic environment and the fish’s body. Note that this description The respiratory system is inherent not only in fish, but in many vertebrate and non-vertebrate inhabitants of the seas and oceans. But read on to find out what is special about the respiratory organs that are found in the body of fish.

Where are the gills located?

The respiratory system of fish is mostly concentrated in the pharynx. It is there that the gas exchange organs of the same name are located on which they are attached. They are presented in the form of petals that allow both air and various vital fluids that are inside each fish to pass through. In certain places the pharynx is pierced by gill slits. It is through them that the oxygen that enters the fish’s mouth with the water it swallows passes.

Very important fact is that, in comparison with the size of the body of many marine inhabitants, their gills are quite large for them. In this regard, problems with the osmolarity of blood plasma arise in their bodies. Because of this, fish always drink sea water and release it through the gill slits, thereby speeding up various metabolic processes. It has a smaller consistency than blood, therefore it supplies the gills and other internal organs with oxygen faster and more efficiently.

The breathing process itself

When a fish is just born, almost its entire body breathes. Each of its organs, including the outer shell, is permeated with blood vessels, so the oxygen that is in sea water constantly penetrates the body. Over time, each such individual begins to develop gill breathing, since the gills and all adjacent organs are equipped with the largest network of blood vessels. This is where the fun begins. The breathing process of each fish depends on its anatomical features, therefore in ichthyology it is customary to divide it into two categories - active breathing and passive. If everything is clear with the active one (the fish breathes “usually”, taking oxygen into the gills and processing it like a person), then with the passive one we will now try to understand it in more detail.

Passive breathing and what it depends on

This type of breathing is characteristic only of fast-moving inhabitants of the seas and oceans. As we said above, sharks, as well as some other representatives of the cartilaginous superclass, cannot remain motionless for a long time, since they do not have a swim bladder. There is another reason for this, namely, this is passive breathing. When a fish swims at high speed, it opens its mouth slightly and water automatically enters. Approaching the trachea and gills, oxygen is separated from the liquid, which feeds the body of the marine fast-moving inhabitant. That is why, being without movement for a long time, the fish deprives itself of the opportunity to breathe, without spending any strength and energy on it. Finally, we note that such fast-moving inhabitants of salt waters include mainly sharks and all representatives of mackerel.

The main muscle of the fish body

The fish is very simple, which, we note, has practically not evolved over the entire history of the existence of this class of animals. So, this organ is two-chambered. It is represented by one main pump, which includes two chambers - the atrium and the ventricle. The fish heart pumps only venous blood. In principle, this type of marine life has a closed system. The blood circulates through all the capillaries of the gills, then merges in the vessels, and from there again diverges into smaller capillaries, which already supply the rest of the internal organs. After this, the “waste” blood collects in the veins (fish have two of them - hepatic and cardiac), from where it goes directly to the heart.

Conclusion

So our short biology lesson has come to an end. The topic of fish, as it turned out, is very interesting, fascinating and simple. The organism of these sea inhabitants is extremely important for study, since it is believed that they were the first inhabitants of our planet, each of them is the key to the solution to evolution. In addition, studying the structure and functioning of a fish organism is much easier than any other. And the sizes of these inhabitants of the aquatic environment are quite acceptable for detailed consideration, and at the same time, all systems and formations are simple and accessible even for school-age children.

Human skeleton: functions, departments

The skeleton is a collection of bones, cartilage that belongs to them, and ligaments connecting the bones.

There are more than 200 bones in the human body. The skeleton weighs 7-10 kg, which is 1/8 the weight of a person.

The following are distinguished in the human skeleton: departments:

• head skeleton(scull), torso skeleton- axial skeleton;
• upper limb belt, lower limb belt- accessory skeleton.

Human skeleton front

Skeletal functions:

• Mechanical functions:

1. support and attachment of muscles (the skeleton supports all other organs, gives the body a certain shape and position in space);
2. protection - the formation of cavities (the skull protects the brain, the chest protects the heart and lungs, and the pelvis protects the bladder, rectum and other organs);
3. movement - a movable connection of bones (the skeleton together with the muscles makes up the motor apparatus, the bones in this apparatus play a passive role - they are levers that move as a result of muscle contraction).

Biological functions:

1. mineral metabolism;
2. hematopoiesis;
3. blood deposition.

Classification of bones, features of their structure. Bone as an organ

Bone- a structural and functional unit of the skeleton and an independent organ. Each bone occupies a precise position in the body, has a certain shape and structure, and performs its characteristic function. All types of tissues take part in bone formation. Of course, the main place is occupied by bone tissue. Cartilage covers only the articular surfaces of the bone; the outside of the bone is covered with periosteum, and the inside is Bone marrow. Bone contains fatty tissue, blood and lymphatic vessels, and nerves. Bone tissue has high mechanical properties, its strength can be compared with the strength of metal. Relative bone density is about 2.0. Living bone contains 50% water, 12.5% ​​organic protein substances (ossein and osseomucoid), 21.8% inorganic mineral substances (mainly calcium phosphate) and 15.7% fat.

In dried bone, 2/3 consists of inorganic substances, on which the hardness of the bone depends, and 1/3 - organic substances, which determine its elasticity. The content of mineral (inorganic) substances in bone gradually increases with age, causing the bones of older and older people to become more fragile. For this reason, even minor injuries in old people are accompanied by bone fractures. The flexibility and elasticity of bones in children depend on the relatively higher content of organic substances in them.

Osteoporosis- a disease associated with damage (thinning) of bone tissue, leading to fractures and bone deformation. The reason is failure to absorb calcium.

The structural functional unit of bone is osteon. Typically, an osteon consists of 5-20 bone plates. Osteon diameter is 0.3 - 0.4 mm.

If the bone plates fit tightly to each other, then a dense (compact) structure is obtained. bone matter. If the bone crossbars are loosely located, then spongy bone substance is formed, which contains red bone marrow.

The outside of the bone is covered with periosteum. It contains blood vessels and nerves.

Due to the periosteum, the bone grows in thickness. Due to the epiphyses, the bone grows in length.

Inside the bone there is a cavity filled with yellow bone marrow.

Internal structure of bone

Classification of bones according to form:

1. Tubular bones- have a general structural plan, they distinguish between a body (diaphysis) and two ends (epiphyses); cylindrical or triangular shape; length prevails over width; On the outside, the tubular bone is covered with a connective tissue layer (periosteum):

• long (femoral, shoulder);
• short (phalanxes of fingers).

Spongy bones- formed predominantly by spongy tissue surrounded by a thin layer of solid matter; combine strength and compactness with limited mobility; The width of the spongy bones is approximately equal to their length:

• long (sternum);
• short (vertebrae, sacrum)
• sesamoid bones - located in the thickness of the tendons and usually lie on the surface of other bones (patella).

Flat Bones- formed by two well-developed compact outer plates, between which there is a spongy substance:

• skull bones (roof of the skull);
• flat (pelvic bone, shoulder blades, bones of the girdles of the upper and lower extremities).

Mixed dice- have a complex shape and consist of parts that differ in function, form and origin; due to their complex structure, mixed bones cannot be classified as other types of bones: tubular, spongy, flat (the thoracic vertebra has a body, an arch and processes; the bones of the base of the skull consist of a body and scales).

The complex of progressive structural features of bony fishes is especially clearly and fully expressed in the youngest and most progressive branch of this class - the bony fishes Teleostei, which includes the vast majority of living forms of this class.

The axial skeleton of bony fishes is composed of numerous bony vertebrae. The vertebral bodies are concave in front and behind - such vertebrae are called amphicoelous. The space formed between the concave surfaces of adjacent vertebrae and the narrow canal running through the center of the vertebral bodies are filled with the remains of the notochord (Fig. 34, 1), which has a beaded shape. The spine is divided into two sections: the trunk (pars thoracalis) and the caudal (pars caudalis); the vertebrae of these sections differ in their structure.

Like cartilaginous fish, the skull of bony fishes consists of two sections: the axial skull, or braincase (neurocranium), and the facial, or visceral, skull (splanchnocranium). But unlike cartilaginous fish, the skull of bony fish is almost entirely formed by bone tissue and consists of numerous individual bones.

In the internal structure of bony fishes, the most striking feature is the appearance of a swim bladder - a hydrostatic organ that increases “buoyancy” and allows the fish to maneuver without significant expenditure of energy. In cartilaginous fish this is only possible during movement, which naturally requires significant energy expenditure. The swim bladder also performs some additional functions: it serves as a resonator for the sounds produced by the fish, can serve as a reservoir for accumulating a reserve supply of oxygen (and in some species, as an organ of air respiration), etc.

The absence of a spiral valve, characteristic of cartilaginous fish, is compensated in bony fish by an increase in the relative length of the intestine and the development of pyloric appendages in many species, which also increase the total absorptive surface of the intestine. These transformations help increase the intensity and efficiency of digestion.

The structure of the genitourinary system of bony fish is peculiar. They, like cartilaginous fish, have mesonephric (trunk) kidneys with ureters corresponding to Wolffian canals. Unlike cartilaginous fish, bony fish have a bladder. As for the genital ducts of bony fishes, they are special education, not homologous to either Wolff or Müller channels. These features arise as a result of changes in the course embryonic development gonads and, apparently, are associated with adaptation to the excretion of a large number of reproductive products; The fertility of bony fish is much higher than that of cartilaginous fish. However, the considered features of the genitourinary system are a specific property only of bony (and some other bony) fish and did not receive further development in the evolution of vertebrates.

The skeleton contains bone tissue; the skull of bony fish is almost entirely formed by bone tissue and consists of numerous individual bones. In the internal structure of bony fishes there is the appearance of a swim bladder, the gills have become not attached plates, but separately hanging petals, covered with an operculum, and there is a bladder.

1) External structure and covers:

The skin is represented by a multilayered epidermis and an underlying corium. Single-celled glands of the epidermis secrete mucus, which is bactericidal and reduces friction. The epidermis and corium contain chromatophore cells with pigments that cause camouflage (cryptic coloration). Some are capable of randomly changing color. The corium contains scales of bone origin:

• 1. Cosmoid scales - bone plates covered with cosmin (dentin-like substance) (in lobe-finned fish);
• 2. Ganoid scales - bone plates covered with ganoid (in ganoid fish);
• 3. Bone scales are modified ganoid scales in which ganoin has disappeared. Types of bone scales:
  • a) Cycloid scales - with a smooth edge (carp-shaped);
  • b) Ctenoids - with a jagged edge (perciformes).

You can determine the age of a fish by its scales: over the course of a year, two concentric rings form on the scales - a wide, light one (summer) and a narrow, dark one (winter). Therefore, two rings (stripes) are one year.

• 2) Internal structure :
  • A) Digestive system:
    • - oral cavity: there are developed teeth that are replaced irregularly throughout life. Some people develop heterodontity (heterogeneity of teeth). There is no language. The glands secrete mucus that does not contain food enzymes; it only helps push through the food bolus.
    • - pharynx: gill rakers of the gill arches are involved in the movement of food. In some, they form a filtering apparatus (planktivores), in some they help push food (carnivores), or grind food (benthivores).
    • - esophagus: short, muscular, imperceptibly passes into the stomach.
    • - stomach: different shapes, some have no stomach. The glands produce hydrochloric acid and pepsin. Therefore, here it is carried out chemical treatment protein food.
    • - intestines: no spiral valve. There are pyloric outgrowths in the initial part of the intestine, increasing the absorption and digestive surface of the intestine. The intestines are longer than those of cartilaginous fish (in some, 10-15 times the length of the body). There is no cloaca, the intestine opens to the outside with an independent anus.
    • - liver: less developed (5% of body weight). Gallbladder and the duct is well developed.
    • - pancreas: unformed, scattered in islets along the walls of the intestines and liver.
  • b) Respiration and gas exchange:

Respiratory organs - gills, consisting of gill filaments, are located on 1-4 gill arches (bone). Interbranchial septa are absent. The gill cavity is covered by bony gill covers. The afferent gill artery approaches the base of the gill arch and supplies capillaries to the gill filaments (gas exchange); The efferent branchial artery collects oxidized blood from the gill filaments.

The act of breathing: when inhaling, the gill covers move to the sides, and their leathery edges with external pressure are pressed against the gill slit and prevent the exit of water. Water is sucked into the gill cavity through the oropharyngeal cavity and washes the gills. When you exhale, the gill covers come together, water pressure opens the edges of the gill covers and is pushed out.

Gills are also involved in the release of metabolites and water-salt metabolism.

In addition to gill breathing, some bony fish have developed:

• 1. Skin respiration (from 10 to 85% in respiration);
• 2. Using the oral cavity (its mucous membrane is rich in capillaries);
• 3. With the help of the epibranchial organ (hollow chambers above the gills with developed folding of the internal walls);
• 4. With the help of the intestines (the swallowed air bubble passes through the intestines, releasing O2 into the bloodstream and taking CO2);
• 5. Swim bladder in open-vesical fish (swim bladder is connected to the esophagus). The main role is hydrostatic, baroreceptor and acoustic resonator;
• 6. Pulmonary respiration (in lobe-finned and lungfishes). The lungs develop from the swim bladder, the walls of which acquire a cellular structure and are intertwined with a network of capillaries.
• V) Circulatory system:

One circle of blood circulation, two-chambered heart, there is a venous sinus. The aortic bulb, which replaces the conus arteriosus, has smooth muscle walls and, therefore, does not belong to the parts of the heart.

Arterial part:

Heart > abdominal aorta > 4 pairs of afferent branchial arteries > gills > 4 pairs of efferent branchial arteries > roots of the dorsal aorta > carotid cephalic circle (to the head) and dorsal aorta (to the internal organs) > caudal artery.

Venous part:

Anterior cardinal veins from the head and subclavian veins from the pectoral fins > ducts of Cuvier > sinus venosus > heart.

Tail vein > renal portal veins > renal portal system > posterior cardinal veins > Cuvier's ducts > sinus venosus > heart.

From the intestine > portal vein of the liver > portal system of the liver > hepatic vein > venous sinus > heart.

Hematopoietic organs are the spleen and kidneys.

d) Excretory system:

Paired mesonephric kidneys > ureters (Wolffian canals) > bladder > independent urinary opening.

In freshwater fish, the kidneys are glomerular (Bowman's capsules with Malpighian bodies are developed). In marine animals, the glomeruli become smaller and simpler. The product released is ammonia.

• 2 types of water-salt metabolism:
  • a) Freshwater type: due to the hypotonicity of the environment, water constantly enters the body through the skin and gills, therefore, the fish are at risk of watering, which leads to the development of a filtration apparatus that allows the removal of excess water (up to 300 ml of final urine per 1 kg of body weight per day ). The loss of salts is avoided by their active reabsorption in the renal tubules.
  • b) Marine type: due to the hypertonicity of the environment, water leaves the body through the skin and gills, therefore, the fish are at risk of dehydration, which leads to the development of agromerular buds (glomeruli disappear) and a decrease in the amount of final urine to 5 ml per 1 kg of body weight per day .
  • d) Reproductive system:
    • >: Testes > seminiferous tubules > vas deferens (independent canals not associated with mesonephros) > seminal vesicle > genital opening.
    • +: Ovaries > posterior elongated sections of the ovaries (excretory ducts) > genital opening.

Most fish are dioecious. Fertilization is external. The female lays eggs (eggs), and the male waters her with milk (sperm).

f) Nervous system and sensory organs:

Similar to those of cartilaginous fish systems.

3) Skeleton and muscular system:

Cartilaginous tissue is replaced by bone tissue: the main (replacement) bones are formed. The second type of bones is formed in the corium: integumentary (cutaneous) bones, which submerge under the skin and form part of the skeleton.

a) Axial skeleton:

It is represented by well-developed bony amphicoelous vertebrae. A distinct notochord runs through and between the vertebral bodies. The vertebral column is represented by the trunk and caudal sections, the structure of which is similar to cartilaginous fish. The vertebrae are connected by articular processes located at the base of the upper arches.

• b) Scull:
  • 1. Brain skull.

Characterized by the presence of a large number of main and integumentary bones.

• - in the occipital region there are 4 occipital bones: the main occipital, 2 lateral and the superior occipital bones.
• - the lateral section is formed by 5 ear bones, 3 orbital bones (ococulosphenoid, main and lateral sphenoid), 2 olfactory bones (unpaired middle olfactory and lateral paired olfactory). All these bones are basic: they develop by ossification of cartilage.
• - the roof of the skull is formed by the integumentary bones: paired nasal, frontal and parietal bones.
• - the bottom of the skull is formed by 2 unpaired cutaneous bones: the parasphenoid and the vomer with teeth.
• 2. Visceral skull:

Maxillary, hyoid, 5 pairs of gill arches and the skeleton of the gill cover. bony fish metabolite sturgeon

• - the jaw arch is divided into primary jaws - ossification of the cartilaginous elements of the jaw arch, and secondary jaws - integumentary bones that strengthen the jaws. From the palatoquadrate cartilage (upper jaw) 3 main bones are formed: palatine (with teeth), posterior pterygoid and quadrate. Between them are the integumentary outer and inner pterygoid bones. From Meckel's cartilage (lower jaw) a replacement articular bone is formed, forming a jaw joint with the quadrate bone. Secondary jaws are represented in the upper jaw by premaxillary and maxillary bones with teeth; in the lower jaw - the dental and angular bones.
• - the hyoid arch is formed by the main bones: hyomandibular, hyoid and unpaired copula. Bony fish are characterized by hyostyly.
• - the skeleton of the operculum is represented by 4 integumentary bones: preopercular, opercular, interopercular and subopercular.
• - gill arches 5 pairs. The first 4 are formed by 4 paired elements connected at the bottom by copulas (they bear gills). The last gill arch does not bear gills and consists of 2 paired elements, to which pharyngeal teeth can be attached (in some).
• V) Skeleton of paired limbs and their girdles:

Paired limbs are represented by pectoral and ventral fins. There are 2 types of paired fins:

• a) biserial type - the fins have a central dissected axis, to which radial segments (lobe-finned and lung-finned) are attached in pairs;
• b) uniserial type - radials are attached only on one side of the central axis (lobe-finned fish).

In ray-finned fish, the basal elements of the fins are reduced, the radials are attached directly to the girdle, and lepidotrichia (cutaneous bone rays that support the fin blade) are attached to the radials.

Shoulder girdle consists of primary and secondary elements. The primary belt is represented by ossified scapulae and coracoid. The secondary belt is represented by a large cleithrum, which, through the supracleithrum, is attached to the occipital region of the skull.

Skeleton of the pectoral fins themselves represented by one row of radials, to which lepidotrichia are attached.

Pelvic girdle represented by a cartilaginous or bony plate lying in the thickness of the muscles, to which the lepidotrichia of the ventral fins are attached through a series of radials.

d) Skeleton of unpaired limbs:

Dorsal fins formed by lepidotrichia, the skeletal basis of which is pterygophores, immersed in the muscles and connected at the lower ends with the upper spinous processes of the vertebrae.

Tail fin: 4 types:

• 1. Protocercal - symmetrical structure, the notochord runs along the middle of the fin (fish larvae).
• 2. Heterocercal - similar to cartilaginous fish (sturgeons).
• 3. Homocercal - equilobed, the upper and lower lobes are the same, but the axial skeleton extends into the upper lobe (most bony fish).
• 4. Diphycercal - single-lobed. The axial skeleton runs along the middle of the fin (lungfishes and lobe-finned fish).

The skeletal basis of the caudal fin is the expanded processes of the terminal vertebrae - hypuralia; the fin blade is supported by lepidotrichia.

Muscular system similar to cartilaginous fish.