Structural feature of all bony fish. The external and internal structure of the fish
Fish are cold-blooded vertebrates that belong to the multicellular subkingdom, the Chordata type. They were able to adapt to a variety of environmental conditions. They live both in freshwater and saltwater reservoirs, up to 10 thousand meters deep, and in drying riverbeds with water from 2 to 50 degrees, etc. Their body temperature is practically equal to the temperature of the water in which they live, and does not exceed it by more than 0.5 - 1 C (the species of tuna fish can have a difference much larger 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 dwellers ( stingrays, flounders);
- streamlined, torpedo-shaped in individuals that spend most of their lives in the water column ( mullet, tuna);
- swept ( pike);
- globular ( bodywork).
Despite the external and internal differences formed by the habitat, the structure of the fish has common characteristics. Like all vertebrates, they have a skeleton with muscles, skin, excretory system, organs of reproduction, senses and respiration, digestive, nervous and circulatory systems.
Skeleton and muscles
Most fish have a bone or cartilage-bone skeleton, but there are also individuals with a cartilaginous skeleton. For example, shark, stingray. This leads to a logical question: How is the structure of bony fish different from cartilaginous?
The structure of bony fish
Structural features of bony fish include the presence of a spine, a brain skull, a skeleton of the limbs and their belts. The basis of the spine is a considerable number of individual bones, the so-called vertebrae. They have a very strong connection, but mobile, because. between them is a cartilaginous layer. The spine is divided into the caudal and, of course, the trunk. The ribs of the 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 caudal region, for obvious reasons, and on the dorsal side of the body. Thanks to the contraction of the muscles, the fish reproduces the movement.
The structure of cartilaginous fish
The cartilaginous skeleton is impregnated with calcium salts, due to which it retains its strength. In particular, the structure of cartilaginous fish can be attributed to the fact that their skull fuses with the jaws (hence the name whole-headed), or creates one or two joints with them (laminabranch). The mouth with enamelled teeth is on the ventral side. There are a pair of nostrils in front of the mouth. The notochord persists throughout life, but gradually decreases in size.Fins
The external structure of the fish has a difference in the fins. Some consist of soft (branched), while others of hard (prickly, may look like a serrated saw or powerful spikes) rays. The fins are webbed or free. They are divided into two groups - paired (abdominal and thoracic) and unpaired (anal, dorsal, caudal and fatty, which not all species have). The bony rays of the fins are aligned with the bones of the limb girdle.Many bony fish according to the nature and presence of rays in the fins, a formula is drawn up. It is widely used in the identification and description of fish species. In the formula, the abbreviation of the fin designations is given in Latin:
BUT- (from lat. language pinna analis) anal fin.
D1, D2 – (pinna dorsalis) dorsal fins. Roman numerals denote prickly, and Arabic numerals denote soft.
P – (pinna pectoralis) pectoral fin.
V – (pinna ventralis) ventral fin.
In cartilaginous fish there are paired pectoral, dorsal and ventral fins, as well as a caudal fin.When swimming fish, the driving force falls on the tail and caudal fin. It is they who push the body of the fish forward with a powerful blow. The tail swimmer is supported by special flattened bones (for example, urostyle, which is translated from Greek as a stick, support, etc.). The anal and dorsal fins help the fish keep its balance. The rudder is the pectoral fins, which move the body of the fish when swimming slowly, and together with the caudal and ventral fins, help to keep balance when the fish is not moving.
In addition, fins can perform completely different functions. For example, in viviparous individuals, the anal, modified fin has become a mating organ. Gourami have thread-like ventral 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. In other individuals, burrowing into the ground, very often fins are completely absent.
Tail fins have the following types:
- Truncated;
- Round;
- Split;
- Lyre-shaped.
The swim bladder allows the fish to be at one or another depth, but here it is already without muscle effort. This important formation is laid as an outgrowth on the dorsal edge of the intestine. Only bottom fish and good swimmers, which for the most part belong to cartilaginous fish, do not have a swim bladder. Due to the absence of this outgrowth, they are forced to constantly be on the move so as not to drown. Skin covering
Fish skin consists of a multi-layered epidermis (or epithelium) and a connective tissue dermis located underneath. In the epithelial layer are numerous glands that secrete mucus. This mucus performs a number of functions - it reduces friction on the water when the fish swims, protects the body of the fish from external influences, and disinfects superficial wounds. The epithelial layer also contains pigment cells, which are responsible for the color of the body of the fish. In some fish, the color varies depending on the 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 the number of scales in different species. Some may be practically without scales at all. Others with large scales. For example, in some carps they can reach a couple of centimeters. However, in general, the body size of a fish is directly proportional to the scales and is determined by the linear equation:
Ln=(Vn/V) |
L- the length of the fish;
ln is the estimated length of the fish in age;
V- length of the scale from the center to the edge;
Vn- distance from the center of the cover (scales) to the annual ring (aged).
Of course, the environment and lifestyle directly affect the structure of the scales. So, for example, swimmer fish, which spend most of their lives in motion, have developed, strong scales, which helps to reduce the friction of the body on the water, and also gives speed.
Specialists highlight three types of scales:
- bone (divided into cycloid - smooth, round and ctenoid, which is characterized by small spikes along the posterior edge);
- ganoid,
- placoid.
bony scales characterized by the presence in its composition of only bone substance. The following types of fish have it: herring, carp, perch.
ganoid scale has the shape of a rhombus and is connected to each other with the help of special joints, which makes it look 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 scale found in fossil fish. It is the most ancient and is, like the ganoid, the shape of a rhombus, but with a spike that protrudes outward. In the chemical composition, the scales have dentin, and the spike is covered with a special enamel - vitrodentin. A special feature is that this type of scale is characterized by a cavity that is filled with loose connective tissue with nerve fibers and even blood vessels. Altered placoid scales are also possible, for example, spines in rays. In addition to rays, sharks also have placoid scales. It is typical for cartilaginous fish.
The scales are located on the body in a row, the number does not change with age, therefore it sometimes serves as a species sign. For example, the lateral line of a pike has 111-148 scales, and a crucian has 32-36.
excretory system
On both sides of the spine, above the swim bladder, the fish have ribbon-like 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 a tortuous renal urinary canal, in which one end increases in the Malpighian body, and the other goes to the ureter. The products of nitrogen decomposition, namely urea, enter the lumen of the tubules and secrete the glandular cells. In the same place, the reverse absorption of microelements and all kinds of vitamins from the filtrate of Malpighian bodies (a glomerulus of arterial capillaries, which is covered by enlarged walls of the tubule and creates a Bowman's capsule), sugars and, of course, water takes place.
The filtered blood flows back into the vascular system of the kidneys, 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, ammonia (NH3) is the final breakdown product.
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 gonads, or gonads, are represented in males by paired milky-white testes, in females by saccular ovaries, the ducts of which open outward through the urogenital opening or genital papilla behind the anus. Fertilization in bony fish, as a rule, external, but in some species, the anal fins of males have been transformed into a copulatory organ - gonopodia, 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 at first feed on the yolk sac.
On the structural features of cartilaginous fish consider internal fertilization. Most of them have a cloaca. Males (males) have several pelvic fins, which form the copulatory organ. By their nature, cartilaginous fish lay eggs or are viviparous.
sense organs
Important sense organs that influence the behavior of fish when searching for and eating food, as well as determine temperature and chemical changes in the water, are: vision, ear, smell, taste and lateral line.Smell and taste
A pair of small nasal pits, which are covered with olfactory epithelium, is the organ of smell. They fish feel chemical irritants from substances dissolved in water. In nocturnal inhabitants, such as carp, bream, eel, the sense of smell is better developed.Not everyone knows that fish have a well-developed taste organ. They define salty, sweet, sour and bitter taste. There are taste buds 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 the eye of fish depend on the species and directly on its habitat. For example, the ability to see in eels and catfish is secondary compared to 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 the eye of a fish, in comparison with the human, is elastic (not able to change shape) and quite hard. In an unexcited state, it is located near the cornea and allows you to see the fish 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 view up to 15 meters in the water, which is shocking. By the size of the eye, which corresponds to the head of a fish, one can determine visual acuity and the ability to see the world around.
The back 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-wave region of the spectrum, which the human eye does not perceive. Also, fish are 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 has a certain wavelength, while the vision of fish and humans is not equally sensitive to light with different wavelengths, i.e. to a variety of colors. The relative susceptibility to light from different wavelengths at low light intensity is also shown. At high, the sensitivity shifts towards longer wavelengths. The amount of daylight that penetrates below 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 much the surface of the water oscillates, i.e. agitated. Rays of light are partially absorbed by water and a fraction of them is scattered by solid microscopic particles that are suspended in water. 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 the water, due to which there are a number of differences with atmospheric visibility:
1. Objects that are under the fish, the individual does not see clearly, but exactly in the place where they actually are.
2. Objects that are in front of or above the fish, the individual sees most clearly.
3. Due to the fact that the eyes of the fish are located on the sides of the head, it can only see in a small space behind, side and front.
4. The fish sees a light cone above it, with which it observes, for example, live or dry food. At the same time, 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 this connection, when viewed from above, a person sees the fish exactly where it actually is. The fish, on the other hand, 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 can appear at the edges of this window, while items directly above the fish are placed in the middle of it.
6. Light rays travel faster in air than in water due to its dense environment. 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 the flow of water, the line of refraction of light.
Lateral line
Of particular importance for fish is the lateral line canal system, which communicates with the external environment through openings. The lateral line stretches along the body of the fish and is able to perceive water fluctuations, the presence of objects in the path of the fish, the speed and direction of currents. Even a blind fish is able to navigate quite well in space.
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 electric 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) stacked in columns that generate an 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 is hundreds of thousands, and sometimes even 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, electric discharges of such fish as eels and rays are dangerous for human life.
Respiratory system
Most fish breathe oxygen dissolved in water using gills. Gill openings are located in the anterior part of the digestive tube. The respiratory process is carried out with the help of movements of the gill covers and the mouth opening, due to which water washes the gill filaments located on the gill arches. In each gill lobe there are capillaries into which the gill artery splits, carrying venous blood from the heart. Having been enriched with oxygen and having lost carbon dioxide, the blood from the capillaries is sent to the efferent branchial arteries, which merge into the dorsal aorta, and through the arteries leaving it, the oxidized blood spreads to all organs and tissues of the fish. Oxygen can also be absorbed by the intestinal mucosa, so some fish 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 include many popular representatives of the aquarium ichthyofauna ( macrapods, gourami, laliuses), have a special organ - the gill labyrinth. Thanks to him, fish have the ability to absorb oxygen from the air. At the same time, if this family for some reason cannot rise to the surface of the water for several hours, then it dies.
The sources of oxygen in aquarium water, as in natural reservoirs, are natural gas exchange with the surrounding air. Aeration of water with microcompressors and pumps improves this gas exchange in the built environment. In natural conditions, waves, rapids, and rifts come to the rescue. Also, a large amount of oxygen in the daytime is supplied by plants, in 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 temperature of the water, the size and type of fish, as well as the degree of their activity.
It is no secret that the solubility of gases decreases with increasing liquid temperature. The oxygen content in water that comes into contact with atmospheric air is usually less than the limiting solubility:
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 favorable 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 individuals. However, some general points can also be noted.The digestive system includes: mouth and oral cavity, pharynx, esophagus, stomach, intestines (large, small and rectum, ending with anus). Some fish species have a cloaca in front of the anus, i.e. the cavity in which the rectum will be, as well as the ducts of the reproductive system and urinary.
The mouth opening of the fish is necessary for receiving, sometimes chewing and swallowing food. There are no salivary glands, but there are taste buds, which were written about earlier. Some species are equipped with tongue and teeth. Teeth can be located not only on the jaws, but also on the palatine bones, pharynx and even tongue. Usually they do not have roots and after the expiration of time they are replaced by new ones. They serve to capture and hold food, and also perform a protective function.
Herbivores mostly do not have teeth.
From the oral cavity, food enters the stomach through the esophagus, where it is processed with the help of 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 types of fish, the stomach can differ in structure, size and even shape: oval, tubes, the letter V, etc.
In some herbivorous species, symbiotic protozoa and bacteria take part in the process of digestion.
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 canal flow into it, which deliver enzymes and bile to the intestine, which break down proteins into amino acids, and fats into fatty acids and glycerol, polysaccharides into sugars.
In addition to the process of splitting substances in the intestine, due to the folded structure of the walls, they are absorbed into the blood, intensively flowing in the posterior region.
The intestine ends with an anus, which is usually located at the end of the body, immediately in front of the genital and urinary openings.
Glands are also involved in the process of digestion in fish: 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.
Autonomic nervous system - 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. Intertwining, the ganglia unite the central nervous system with the autonomic. These systems are interchangeable and independent of each other.
The central nervous system is located along the entire body: part of it, which 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 divisions: the cerebellum, middle, oblong, diencephalon and forebrain. The gray matter of the forebrain, in the form of striated 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, flock formation, territory protection and aggression) and movement.
The optic nerves branch off from the diencephalon, so it is responsible for the vision of the fish. The pituitary gland (pituitary gland) adjoins its lower side, and the epiphysis (pineal gland) adjoins the upper part. The pineal and pituitary glands are endocrine glands. Also, the diencephalon is involved in the coordination of movement and the functioning of other sense organs.
In fish, the cerebellum and midbrain are best developed.
midbrain includes the largest volume. It has the shape of two hemispheres. Each lobe is the primary visual center that processes the signals of the organs of taste, vision, and perception. There is also a connection with the spinal cord, the cerebellum.
Cerebellum has the appearance of a small tubercle, which adjoins the medulla oblongata from above. 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 balance, as well as muscle work. It is connected to lateral line receptors and synchronizes the work of other parts of the brain.
Medulla smoothly passes into the dorsal and consists of a white-gray substance. It regulates and controls the functioning of the spinal cord and the autonomic nervous system. It is also important for the circulatory, musculoskeletal, respiratory and other systems of fish. Damage to this part of the brain, the fish immediately dies.
Like many other systems and organs, the nervous system has a number of differences depending on what kind of fish. So, for example, individuals may differ in the level of formation of the lobes of the brain.
Structural features of representatives of the class cartilaginous fish (stingrays and sharks) include: olfactory lobes and a developed anterior brain. Bottom and sedentary individuals have a small cerebellum and a well-developed medulla oblongata and anterior sections of the brain, 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 for the visual lobes. But in deep-sea individuals, the visual lobes of the brain are weak.
The spinal cord is a continuation of the medulla oblongata. Its peculiarity is that it quickly regenerates and recovers when damaged. Inside it is gray matter, white - outside.
The spinal cord serves as a conductor and catcher of reflex signals. Spinal nerves branch off from it, which innervate the surface of the body, the muscles of the body, 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 work of the nervous system of fish is the reflex. For example, if the fish are fed for a long time in the same place, then they will prefer to swim there. In addition, fish can develop reflexes to light, fluctuation and temperature of water, smell and taste, and shape.
It follows from this that, if desired, an aquarium fish can be trained and certain behavioral reactions can be developed from 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 in general 10-16%.In addition, fish have low blood pressure and a low heart rate of 17 to 30 beats per minute. However, at low temperatures, it can decrease to 1-2. Fish that endure freezing into ice in the winter season do not have a heart pulsation at all during this period.
Another difference in the circulatory system of mammals and fish is that the latter have a small amount of blood. This is explained by the horizontal position of the life of fish, as well as the habitat, where the force of gravity has an effect on the body much less than in the air.
The heart of fish is two-chambered and consists of one atrium and ventricle, arterial cone and venous sinus. Fish have only one circle of blood circulation, except for brush-finned and lungfish. Blood moves in a vicious circle.
From the ventricle comes the abdominal aorta, from which four pairs of branchial arteries branch off. These arteries split in turn into capillaries, in which the blood is enriched with oxygen. Oxidized blood through the gill arteries enters the roots of the dorsal aorta, which divides into the internal and external carotid arteries, which merge into the dorsal aorta, and from it into the atrium. Thus, all tissues of the body are saturated with the most 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 ability of hemoglobin in the blood may vary. So, for example, fast-swimming individuals living in waters with a good oxygen content have cells with an excellent ability to bind oxygen. Unlike mammalian erythrocytes, fish have a nucleus.
If arterial blood is enriched with oxygen (O), then it is painted in a bright scarlet tone. Venous blood, which is rich in carbon dioxide (CO2) and poor in oxygen, is dark cherry.
It is noteworthy that the body of the fish has the ability to hematopoiesis. Most organs, such as: spleen, kidneys, gill apparatus, intestinal mucosa, vascular endothelium and epithelial layer of the heart, lymphoid organ, can create blood.
At the moment, 14 systems of blood groups of fish are noted.
The complex of progressive features in the structure of bony fishes is especially clearly and fully expressed in the youngest and most progressive branch of this class, Teleostei bony fishes, which includes the vast majority of living forms of this class.
The axial skeleton of bony fish 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 a narrow canal penetrating the center of the vertebral body are filled with remnants of a notochord (Fig. 34, 1), which has a beaded shape. The spine is divided into two sections: trunk (pars thoracalis) and tail (pars caudalis); the vertebrae of these departments differ in their structure.
Like cartilaginous fish, the skull of bony fish consists of two sections: the axial skull, or braincase (neurocranium), and the facial, or visceral, skull (splanchnocranium). But unlike the cartilaginous ones, the skull of bony fishes is almost entirely formed by bone tissue and consists of numerous individual bones.
In the internal structure of bony fish, the most striking feature is the appearance of a swim bladder - a hydrostatic organ that increases "buoyancy" and allows fish to maneuver without a significant expenditure of energy. In cartilaginous fish, this is possible only when moving, which, of course, requires a significant expenditure of energy. The swim bladder also performs some additional functions: it serves as a resonator for sounds made by fish, it can serve as a reservoir for accumulating a reserve supply of oxygen (and in some species it can also be an organ of air breathing), etc.
The lack of a spiral valve characteristic of cartilaginous fishes is compensated in bony fishes by an increase in the relative length of the intestines and by the development of pyloric appendages in many species, which also increase the total absorptive surface of the intestines. These transformations 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 the wolf channels. Unlike cartilaginous fish, bony fish have a bladder. As for the genital ducts of bony fish, they are special formations that are not homologous to either Wolffian or Müllerian canals. These features arise as a result of changes in the course of embryonic development of the gonads and, apparently, are associated with adaptation to the excretion of a large number of reproductive products; the fecundity of bony fish is much higher than that of cartilaginous ones. However, the considered features of the genitourinary system are a specific property of only bony (and some other bony) fish and have not been further developed 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 fish - the appearance of a swim bladder, the gills did not become accreted plates, but separately hanging petals, covered with a gill cover, there is a bladder.
Due to the fact that every creature is endowed with everything, we get something without which we cannot live - 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 it is much less than in the air. It is because of this that the structure of the body of this biological species is so different from all backbone terrestrial creatures. Well, let's consider all the structural features of fish, their respiratory system and other vital organs.
Briefly about fish
To begin with, let's try to figure out what kind of creatures they are, how and with what they live, what kind of relationship they have with a person. Therefore, now we begin our biology lesson, the topic is "Sea fish". 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 eaten.
It is also believed that fish were at the dawn of evolution. It is these creatures that could live under water, but did not yet have jaws, were once the only inhabitants of the Earth. Since then, the species has evolved, some of them have turned into animals, some have remained under water. That's the whole lesson of biology. 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 the study of these creatures from a more professional point of view.
General scheme of the structure of fish
In general, we can say that the body of each fish is divided into three parts - the head, trunk and tail. The head ends in the region of the gills (at their beginning or end, depending on the superclass). The body ends on the line of the anus in all representatives of this class of marine life. The tail is the simplest part of the body, which consists of a rod and a fin.
The shape of the body strictly depends on the living conditions. Fish that lives in the middle water column (salmon, shark) has a torpedo-shaped figure, less often - swept. 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 take on a more agile shape that has much in common with snakes. For example, an eel is the owner of a strongly elongated body.
Business card of a fish - 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 marine inhabitants. What are they?
So, the fins are paired and unpaired. Pairs include chest and abdominal, which are symmetrical and move synchronously. Unpaired are presented in the form of a tail, dorsal fins (from one to three), as well as anal and adipose, which is located immediately behind the dorsal. The fins themselves are composed of hard and soft rays. It is on the basis of 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 in Latin letters (A - anal, P - thoracic, V - ventral). Further, Roman numerals indicate the number of hard rays, and Arabic - soft.
Fish classification
Today, conditionally, all fish can be divided into two categories - cartilaginous and bone. The first group includes such inhabitants of the sea, the skeleton of which consists of cartilage of various sizes. This does not mean at all that such a creature is soft and incapable of movement. In many representatives of the superclass, cartilage hardens, and in its density becomes almost like bones. The second category is bony fish. Biology as a science claims that this superclass was the starting point of evolution. Once within its framework there was a long-extinct lobe-finned fish, from which, perhaps, all land mammals originated. Next, we will take a closer look at the structure of the body of the fish of each of these species.
cartilaginous
In principle, the structure is not something complicated and unusual. This is an ordinary skeleton, which consists of very hard and durable cartilage. Each compound is impregnated with calcium salts, thanks to which strength appears in cartilage. The notochord keeps its shape throughout life, while it is partially reduced. The skull is connected to the jaws, as a result of which the skeleton of the fish has an integral structure. Fins are also attached to it - caudal, paired ventral 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 terrestrial mammals.
How do cartilage breathe
The respiratory system of cartilage is represented primarily by gill slits. They number 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 is that they lack a swim bladder. That is why they are forced to constantly be in motion, so as not to go to the bottom. It is also important to note that the body of cartilaginous fish, which a priori live in salt 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 superclass of bones 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 - cerebral and visceral. The second includes the jaw and hyoid arches, which are the main components of the jaw apparatus. Also in the skeleton of bony fish there are gill arches that 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.
Respiratory apparatus of bone inhabitants of the sea
Probably, it has already become clear to everyone that the respiratory system of bony fish mainly consists of gills. They are located on the gill arches. Gill slits are also an integral part of such fish. They are covered with a lid of the same name, which is designed so that the fish can 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 under 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.
The structure of the gills
Gills are a unique organ that was previously inherent in all primary water creatures that lived on Earth. It is the process of gas exchange between the hydro-environment and the organism in which they function. The gills of the fish of our time are not much different from those gills that were inherent in 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 performs the process of gas exchange between the aquatic environment and the body of the fish. Note that this description of the respiratory system is inherent not only in fish, but in many vertebrate and non-vertebrate inhabitants of the seas and oceans. But about the fact that it is precisely those respiratory organs that are in the body of fish that are special in themselves, read on.
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 are fixed. They are presented in the form of petals that pass through themselves both air and various vital fluids that are inside each fish. In certain places, the pharynx is pierced by gill slits. It is through them that oxygen passes, which enters the mouth of the fish with the water it swallows.
A very important fact is that, compared to the body size of many marine life, their gills are quite large for them. In this regard, in their bodies there are problems with the osmolarity of the blood plasma. Because of this, fish always drink sea water and release it through the gill slits, thereby speeding up various metabolic processes. It has a lower consistency than blood, therefore it supplies the gills and other internal organs with oxygen faster and more efficiently.
The process of breathing
When a fish is just born, almost its entire body breathes. Blood vessels permeate each of its organs, including the outer shell, because the oxygen that is in sea water constantly penetrates into the body. Over time, each such individual begins to develop gill breathing, since it is the gills and all adjacent organs that 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 breathing. If everything is clear with the active one (the fish breathes “usually”, taking oxygen into the gills and processing it like a person), then we will now try to understand the passive one in more detail.
Passive breathing and what it depends on
This type of breathing is peculiar only to fast-moving inhabitants of the seas and oceans. As we said above, sharks, as well as some other representatives of the cartilaginous superclass, cannot be 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 and water automatically enters. Approaching the trachea and gills, oxygen is separated from the liquid, which nourishes the body of a 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 mackerels.
The main muscle of the fish body
A very simple fish is, which, we note, in the entire history of the existence of this class of animals, practically did not evolve. So, this body they have two chambers. 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. Blood circulates through all the capillaries of the gills, then merges in the vessels, and from there again diverges into smaller capillaries that already supply the rest of the internal organs. After that, the “waste” blood is collected in the veins (there are two of them in fish - hepatic and cardiac), from where it goes directly to the heart.
Conclusion
This is the end of our short biology lesson. The theme of fish, as it turned out, is very interesting, fascinating and simple. The organism of these inhabitants of the sea 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 unraveling 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 water stochia are quite acceptable for detailed consideration, and at the same time, all systems and formations are simple and accessible even for school-age children.
Detailed solution paragraph 21 in biology for students in grade 7, authors V. V. Latyushin, V. A. Shapkin 2014
What are the distinguishing features of fish?
Fish live only in water, have a streamlined body, swim bladder, bony scales, gills breathe, move with the help of fins.
What is the difference between cartilaginous fish and bony fish?
The skeleton of cartilaginous fish does not ossify. They have gill covers and a swim bladder. The mouth opening is transverse, located on the underside of the head.
Questions
1. What is the peculiarity of the structure of all bony fish?
Bony fish have an elongated body, a pointed head merged with the body, the skin is covered with bony scales, there are fins, a swim bladder, a specific sensory organ is the lateral line.
2. How do bony fish differ in external and internal structure from previously studied chordates?
Bony fish have a bone skeleton, a skull with jaws. They have more developed sense organs.
3. What is a sideline?
The lateral line is a kind of sensory organ that perceives the speed and direction of the flow of water.
Tasks
Helminthiases
OPISTORCHIASIS
PREVENTION MEASURES
The main cause of infection with opisthorchiasis is eating raw infected fish. Conventional cooking - boiling or frying for 25-30 minutes - allows you to completely eliminate the threat of infection with opisthorchiasis. When salting, the salt concentration should be at least 14% of the weight of the fish, the salting should be carried out for 2 weeks. Strong freezing can also destroy opisthorchiasis pathogens. The temperature must be maintained at -18 ... -20 ° C during the day.
In no case should you feed raw fish, its insides to dogs, cats and other carnivores. They not only become ill with opisthorchiasis themselves, but also become a source that supports the disease in the area, and contribute to its wider spread.
DIPHILLOBOTRIOSIS
Sexually mature helminth releases eggs, which enter the external environment with faeces. If the eggs are in the water, they develop, and after a few days the larvae emerge from the eggs. Cyclopes and diaptomuses (small crustaceans that fish feed on) swallow the larvae, and after 3-4 weeks they turn into procercoids.
Prevention measures are similar to those for opisthorchiasis. You can not eat poorly cooked and fried fish, raw caviar, stroganina. Plerocercoids of the tapeworm die during deep freezing (-20 ° C and below). Most often, people become infected with diphyllobothriasis by eating lightly salted pike caviar.
CLONORCHOSIS
It is caused by a trematode that lives in the liver, gallbladder and other organs of humans and animals. Development occurs with the participation of two intermediate hosts - a mollusk and a fish. More than 70 species of fish serve as the second intermediate host, through which the pathogen enters humans. The disease is common in the Far East, in the Amur basin.
The main measure of prevention is the refusal to eat raw, poorly dried and poorly salted fish.
METAGONIMOSIS
Human infection occurs when eating poorly cleaned, non-disinfected fish. Do not allow individual scales adhering to the hands to enter the mouth. In this regard, smokers are more likely to get metagonimiasis than non-smokers.
NANOPHYETOSIS
Nanophyetosis has been registered in the Far East.
METHORCHOSIS
DIOCTOPHIMOSIS
Prevention consists in careful culinary processing of fish. You can not drink raw water from reservoirs in the foci of dioctophymosis.
GNATHOSMOSIS
Prevention of the disease - processing of fish before its use.
DISEASE PREVENTION
In the vast majority of cases, human infection occurs when eating raw, undercooked and undercooked fish. Careful culinary processing is a reliable way to prevent diseases, the source of which is fish. For example, tapeworm larvae can be found in both lake and marine fish. If the fish is treated appropriately, then the tapeworm larvae will die. Tapeworm larvae die at a temperature of +55 ° C, i.e., if the fish is boiled or fried in the usual way, the larvae will be killed. The duration of cooking should be at least 10-15 minutes. A reliable way to avoid infection is to freeze the fish. Fish weighing less than one kilogram is frozen in ordinary home freezers in 10 hours. In large fish, tapeworm larvae are destroyed if it is kept in the freezer for one day. In other cases, disinfection of fish by deep freezing is recommended. At a temperature of -20 ° C, the fish must be kept for at least 3 days, at a temperature of -8 ... -10 ° C - 3-4 weeks. The larvae also die with abundant salting. Salt must be taken in an amount of at least 12% of the weight of the fish. Keep fish in salt for at least 5 days before eating. When frying, the size of the pieces of fish is more important than their weight. Small fish should be fried for at least 10 minutes. Fish weighing 700-1200 g or fillet 2-3 cm thick are fried for 15-20 minutes. Pieces of fish thicker than 6 cm, as well as large uncut fish that have not had their spine removed, should be fried for at least 40 minutes. Hot smoked fish, as well as carefully baked over an open fire, are harmless.
It is better not to smoke fish (cold and hot) caught from a reservoir where there is a disease, since at home it is difficult to achieve uniform and sufficiently deep heating of fish, which is obtained at industrial fish processing plants.
It is forbidden to feed raw fish from unfavorable water bodies to animals. The insides and scales after cutting the fish must be destroyed, preventing the possibility of eating them by domestic or wild animals. This simple measure allows you to stop the spread of diseases in other water bodies.
Treatment of helminthic diseases should be carried out only under the guidance of a physician. Self-medication is unacceptable. It should be remembered that alcohol in the least does not play a preventive role in helminthiasis. Surrounded by cysts and dense shells, helminths and their larvae have a very perfect enzymatic defense mechanism and withstand the action of digestive juices, even resist many potent substances, not to mention alcohol solutions. In this regard, it is forbidden to drink alcohol while fishing. An intoxicated person loses control over his actions, loses a sense of vigilance, while the risk of infection increases many times over.
Make a memo for tourists vacationing on the coast of the seas and oceans, where sharks, moray eels and other dangerous fish live.
The first and most important rule is not to swim in unfamiliar places.
Rules of conduct: The best precaution is to stay away from sharks. Do not swim in the open sea at night - sharks usually hunt at night. You can't feed the sharks! And if it suddenly happened that you found these predators in dangerous proximity - do not panic, do not hit the water with your feet and hands, do not run away! Face the shark, showing calmness and friendly intentions. If the shark attacks, approaching you in vicious circles, then it makes sense to swim towards it with rhythmic strokes. When a shark attacks, you need to strike it with a fist with your foot or with a camera right in the nose, try to grab it by the fin and swim close by until there is an opportunity to escape or the shark swims away. There were cases when even great white sharks stopped attacking a person after they received a decisive rebuff from him.
Barracuda
Rules of conduct: Do not approach, do not feed, behave calmly! If you were attacked by a barracuda, you need to disinfect the wounds and consult a doctor.
These cigar-like fish, up to two meters long, prefer to hunt in packs and often accompany sharks. The huge mouth of the barracuda is studded with large sharp teeth. In a school of fish, they feel confident, not shy and can attack a lone scuba diver. However, most cases of attacks on people were recorded in troubled waters. Most likely, they mistook the swimmer's arm or leg for a fish.
Moray eels are often found in coral reefs, and due to their long serpentine body, which can reach a length of 3 meters, and their mouths dotted with numerous needle-shaped teeth, they inspire natural fear. But, despite its appearance, the moray eel is not dangerous to humans, if it is not teased. Moray eels hunt at night, and during the day they hide in the crevices of reefs, putting out only their heads. Moray eels, as a rule, react calmly to cameras and a flash, but if you annoy the moray eel, for example, try to stick your hand into its hole, painful lacerations are guaranteed. In addition, the moray eel will not disengage the jaws as long as it is alive.
Rules of conduct: Do not get too close to the moray eel. Do not reach out to her hands, do not throw food and do not put your hand into holes and crevices.
If, nevertheless, the moray eel attacked, it is necessary to treat the wound with antiseptic agents as soon as possible. Their teeth are dirty and the bite usually causes a serious infection, so you should immediately consult a doctor.
Human skeleton: functions, departments
The skeleton is a collection of bones, cartilage belonging to them and ligaments connecting the bones.
There are more than 200 bones in the human body. The weight of the skeleton is 7-10 kg, which is 1/8 of the weight of a person.
The human skeleton has the following departments:
- head skeleton(scull), torso skeleton- axial skeleton;
- upper limb belt, lower limb belt- additional skeleton.
Human skeleton front
Skeleton Functions:
- Mechanical functions:
- support and fastening of muscles (the skeleton supports all other organs, gives the body a certain shape and position in space);
- protection - the formation of cavities (the cranium protects the brain, the chest protects the heart and lungs, and the pelvis protects the bladder, rectum and other organs);
- movement - a movable connection of bones (the skeleton, together with the muscles, makes up the motor apparatus, the bones in this apparatus perform a passive role - they are levers that move as a result of muscle contraction).
- mineral metabolism;
- hematopoiesis;
- deposition of blood.
Classification of bones, features of their structure. Bone as an organ
Bone- structural and functional unit of the skeleton and an independent organ. Each bone occupies an exact position in the body, has a certain shape and structure, and performs its own function. All types of tissues are involved 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 bone marrow is located inside. Bone contains adipose tissue, blood and lymphatic vessels, and nerves. Bone tissue has high mechanical properties, its strength can be compared with the strength of metal. The relative density of bone tissue is about 2.0. Living bone contains 50% water, 12.5% protein organic matter (ossein and osseomucoid), 21.8% inorganic minerals (mainly calcium phosphate), and 15.7% fat.
In the dried bone, 2/3 are inorganic substances, on which the hardness of the bone depends, and 1/3 are organic substances, which determine its elasticity. The content of mineral (inorganic) substances in the bone gradually increases with age, as a result of which the bones of the elderly and old people become more fragile. For this reason, even minor injuries in the elderly are accompanied by bone fractures. The flexibility and elasticity of bones in children depend on the relatively high content of organic substances in them.
Osteoporosis- a disease associated with damage (thinning) of bone tissue, leading to fractures and bone deformities. The reason is not the absorption of calcium.
The structural functional unit of the bone is osteon. Usually osteon consists of 5-20 bone plates. The diameter of the osteon is 0.3 - 0.4 mm.
If the bone plates are tightly adjacent to each other, then a dense (compact) bone substance is obtained. If the bone crossbars are located loosely, then a spongy bone substance is formed, in which the red bone marrow is located.
Outside, 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 is a cavity filled with yellow marrow.
The internal structure of the bone
Bone classification in the form:
- tubular bones- have a general structural plan, they distinguish between the body (diaphysis) and two ends (epiphyses); cylindrical or trihedral shape; length prevails over width; outside the tubular bone is covered with a connective tissue layer (periosteum):
- long (femoral, shoulder);
- short (phalanges of fingers).
- long (sternum);
- short (vertebrae, sacrum)
- sesamoid bones - located in the thickness of the tendons and usually lie on the surface of other bones (patella).
- skull bones (skull roof);
- flat (pelvic bone, shoulder blades, bones of the belts of the upper and lower extremities).