Fish bones and scales, their structure and dielectric properties gojaev em.m., sh.v. alieva, n.b. nadirova. Common representatives of fish without scales What scales do bony fish have

Fish scales are always a derivative of the skin itself (corium), and only sometimes, in addition to the corium, the epidermis also takes a secondary part in its formation.

There are four main types of fish scales: placoid, cosmoid, ganoid and bone.

placoid scale the most primitive and of exceptional comparative anatomical interest, since it gives rise not only to ganoid and bone scales, but also to teeth. In the shark, as already indicated, the teeth represent true placoid scales. These teeth are quite homologous to the teeth of all higher classes, up to mammals, in which the teeth also consist of dentin, are covered with an ectodermic substance - enamel and contain an internal cavity filled with pulp.

Cosmoid Scale- a special type of scale that is found in some fossil bony fish and is found in modern coelacanth.

It is devoid of ganoin and its surface layer consists of cosmin, which in its structure consists of many individual dentin teeth fused with each other.

ganoid scale It is characteristic only of a very few modern fish (multifinned and caiman), but in fossil fish it was very widespread. In a typical case, ganoid scales have the form of flat rhombic plates, which are arranged in oblique rows and are connected to each other using special joints, so that a continuous shell is formed that covers the entire body of the animal.

The outer layer of the ganoid scales consists of a special very solid substance - ganoin, the lower one is made of bone tissue. Ganoid scales are formed in the connective tissue and therefore are never covered with enamel. The lower, bony layer of the ganoid scale appears to be formed from dentin into which bone cells penetrate. In contrast to the placoid scale, the ganoid scale does not change, being formed for life. The evolution of the scales of fossil fish undoubtedly proves that the ganoid scales arose by the fusion of the main plates of individual placoid scales with the underlying bone plates. From above, these scales are covered with ganoin.

bone scales characteristic of all modern bony fish (Osteichthyes), with the exception of multifinned, coelacanth and caiman fish. In a typical form, bone scales are bone plates of various sizes, overlapping each other in a tile-like manner with their edges. They are constantly growing, forming growth rings along the periphery of the plate. Ichthyologists use these annual rings to determine the age of fish. Percids are characterized by ctenoid scales with spines along the posterior edge of the scales, while cyprinids and salmonids are characterized by smooth cycloid scales without teeth. In many bottom fish (catfish, eels), the scales are completely reduced. Sturgeons have special bony scales that form five longitudinal rows of scutes with small star-shaped scales between them. In many fish, bony scales form bony spikes on the fins.

(according to Goodrich):

1 - outer surface, 2 - ganoin layers, 3 - tubules in the cosmine layer, 4 - isapedin layers

The color of fish depends on a number of reasons. For example, the silvery sheen, characteristic not only of scales, but also of many internal organs of fish (swim bladder, peritoneum), is due to the presence of guanine. Guanine from the scales of some fish (bleaks) is used for technical purposes (for example, for making artificial pearls). In addition, the color of fish, like other animals, is due to the presence in the skin of special densely colored pigment cells - chromatophores. Under the influence of nervous stimulation, chromatophores can contract and expand, which determines the ability of many fish to change their color to match the color of the surrounding background.

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Material and equipment. A set of fixed fish - 20-30 species. Preparations: scales of various fish species. Tables: The structure of various types of fish scales; The structure of the lateral line of fish; Photographs of the scales of various fish species. Tools and equipment: MBS-9; glass slides; bath; tweezers; dissecting needles (one set for each student).

Exercise. When doing work, you need to consider using a set of fish: the lateral line: complete and incomplete, located on the back and passing along the belly; and also indicate fish with several lateral lines; identify the heads of herrings with seismosensory channels and gobies with genipores.

Compose and write down the lateral line formula for the type of fish indicated by the teacher.

Examine placoid and two types of bone scales under binoculars on training preparations, ganoid scales on the upper lobe of the caudal fin of sturgeons, find fulcra and write down the names of fish whose bodies are completely covered with ganoid scales

Sketch the placoid scales of a shark, the ganoid scales of an armored pike, the tail fin of a sturgeon fish with fulcra; cycloid scales of a representative of salmon, carp and cod fish, ctenoid perch fish. Mark the center of the scale, front and back.

Find fish with small and large scales, devoid of scales; pay attention to the shape of their body; link the size of the scales with the nature of the movement of the fish. Find fish with bony scutes and plates.

Lateral line(Linealateralisll) - a kind of sensory organ of fish that perceives low-frequency vibrations of water, is a subcutaneous canal lined with sensitive epithelial cells with nerve endings suitable for it. The channel communicates with the external environment through openings penetrating the scales or integuments of the body. The lateral line is of systematic importance. Her appearance is very diverse. In most fish, the lateral line runs in the form of a straight line along the sides of the body from the head to the caudal fin (bream, carp, perch, etc.). Such a lateral line is called complete. In some fish species, the lateral line forms a sharp bend above the pectoral fins (sabrefish, halibut). In smelt and crownfish, the lateral line is incomplete, it occupies several scales. The lateral line can be located on the belly (garfish) or on the back (gerbils). Greenlings have 4-5 pairs of lateral lines, but Toteniaceae have 1-3 pairs. Herring, goby and some other fish do not have a lateral line. Its function is performed by a highly developed system of sensory channels on the head or genipores. Fish with a lateral line (cod, navaga) also have sensory canals and genipores (Fig. 21). The characteristic of the lateral line can be written by the formula. To draw up the lateral line formula, the number of scales along the lateral line, above and below it is calculated. So, the formula of the lateral line of the ide:, which means: 56 - the smallest number of scales for the species along the lateral line; 61 - the largest number of scales for the species along the lateral line; 8-9 - the number of scales above the lateral line to the dorsal fin; 4-5 - the number of scales under the lateral line to the ventral fins. It is not always possible to accurately calculate above and below the lateral line, therefore, sometimes they are limited to calculating the scales only along the lateral line. In this case, the ide formula will look like this: ll=56-61.

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Figure 21 - Genipores and sensory channels:

1 - on the head of a cod; 2 - Navaga on the head.

Types of fish scales. One of the characteristic features of fish is the presence of skin formations in them - scales. Three main types of scales are distinguished in fish, differing both in shape and in the material from which they are built. These are placoid, ganoid and bone scales (Fig. 22).

http://www.livejournal.com/users/bapbap/

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Figure 22 - Types of scales:

A- placoid; b- ganoid; V– cycloid; G- ctenoid; 1 - the center of the scale; 2 - forward radius; 3 - back radius; 4 - power channels.

The placoid scales, called skin teeth, consist of a plate lying in the skin and a spike sitting on it, covered with a layer of enamel; the tip of the spike extends outward through the epidermis. The basis of the placoid scale is dentin, a solid organic substance with calcium salts. Inside the scales is a cavity with blood vessels and nerve endings. The placoid scales are located on the body of the fish in diagonal rows, with each scale lying freely in the skin and not connected with the neighboring one, which does not prevent the lateral mobility of the fish.

The spikes of most sharks are directed towards the tail with their tips, which creates a streamlined body. Placoid scales are characteristic of cartilaginous fish. Modifications of the placoid scales are the teeth of sharks and rays, spines in the dorsal fins of horned and prickly sharks, and various kinds of spiny plates on the body of rays. During life, the placoid scale undergoes repeated changes.

Many fossil lobefins, modern coelacanths, and fossil lungfish have cosmoid scales. In origin, cosmoid scales are fused and highly modified placoid scales. In the living coelacanth, the scales consist of four layers: surface (enamel-like) with teeth and pores; spongy-bone; bone spongy; lower, consisting of dense bone plates.

Ganoid scales arose from the cosmoid. It consists of a bone rhombic-shaped plate with a lateral hook-shaped protrusion, thanks to which the scales are tightly connected to each other, forming a shell on the body of the fish. From above, the scales are covered with a dentin-like substance - ganoin. Such scales were characteristic of fossil paleonisks and performed a protective function. Of the living fish, such scales are multi-feathered (they have cosmoid-ganoid scales), shell-shaped (they have ganoid scales). In sturgeons, the remains of ganoid scales are preserved on the upper lobe of the tail. Modifications of the ganoid scales are fulcra - saddle-shaped formations located along the outer edge of the fins of armored pikes and multifins, and in sturgeons - along the outer edge of the upper lobe of the caudal fin.

Bone scales are characteristic of most modern bony fish. Phylogenetically represents a modification of the ganoid scale. It has the appearance of thin rounded plates lying on the body of the fish in skin pockets; one end of it is rounded, the other freely rests on the neighboring scales. The appearance of bony scales contributed to the development of lateral mobility of fish, a decrease in their mass, and maneuverability of movement. In addition, the tiled arrangement eliminates the possibility of vertical folds in the skin during lateral movements, thus contributing to the maintenance of a smooth, well-streamlined body surface. The scales consist of a basal lamina of bony origin, consisting of parallel fibers and a hard, mineralized upper hyalodentin layer. The hyalodentine layer has irregularities in the form of concentrically located rollers - sclerites. The scales grow as a lower underlying layer: under the first plate, which is laid in the fry, a new, larger diameter appears. With further growth for the next year, another plate of a larger diameter is laid from below. On the edges of the newly formed plates protruding from under the old plate, there is a hyalodentin layer in the form of sclerites. The smallest plate on top is the central one, the oldest, the largest in diameter; below is the youngest. As a result of growth, the central part of the scale becomes denser than its edges. During the period of slow growth (in autumn and winter), sclerites on the outer surface of the scales are laid close to each other or not at all. During the period of intensive growth (spring and summer), sclerites are laid at a distance from each other. The boundary between the closely spaced sclerites of autumn growth and the widely spaced sclerites of spring-summer growth is the annual or annual ring. In addition to annual rings, additional rings may form on the scales during the period of slow growth. The part of the scale covered by the overlying adjacent scale is called the anterior, it differs markedly from the free uncovered - the posterior and is separated by a clearly distinguishable border. The front edge of the scales in most fish is uneven, wavy, which helps to fix the scales in the skin pocket. At the intersection of the line separating the border of the anterior and posterior parts of the scale and the middle longitudinal diagonal lies the center of the scale. Radial strips depart from it - scale supply channels (see Fig. 22). The center of the scale does not necessarily occupy a central position on the scale. It may be displaced towards the posterior margin of the scale.

Due to mechanical damage, individual fish scales often fall out, and new regenerated scales grow in their place. Its center is devoid of a regular sclerite structure and consists of cracks in the main plate extending in different directions. The correct sclerite sculpture of the upper scale layer starts from the year when the scales were newly formed. Such scales are unsuitable for age determination.

Bone scales are of two types: cycloid, with a smooth trailing edge, and ctenoid, on the back, free from the pocket edge of which there are spines (ktenii). Ctenias are visible only with magnification, but are clearly distinguishable by touch, therefore, fish with ctenoid scales have a rough body surface. Cycloid scales are characteristic of low-organized fish of the herring-like, pike-like, and other orders. Ctenoid scales are characteristic of highly organized fish (perciformes, flatfishes). However, this position is not absolute, and fish with cycloid scales are found in these orders. In some species (polar flounder), females have cycloid scales, males - ctenoid. Merow perches have ctenoid scales on their backs and cycloid scales on their belly. In an ordinary perch, the body is covered with ctenoid, and the cheeks with cycloid scales.

The size of the scales is closely related to the ways in which the fish move. In fish with eel-like and ribbon-like body shapes, swimming due to the strong bending of the body, the scales are small (acne, catfish), and in some cases this method of movement leads to its disappearance (moray eels). Small scales are characteristic of fish that move in the scombroid type due to the very high frequency of transverse locomotor bending of the body, in which the presence of scales would impede lateral bending of the body, and with an increase in the frequency of bending, the scales decrease in size. In mackerels in the anterior part of the body, at the pectoral fins and on the back, where lateral bendings are practically absent, the scales are preserved and are larger, forming the so-called corset. Fish with a tall body tend to have larger scales. The largest scales are in sedentary fish, most of which are inhabitants of stagnant waters or coral reefs (spar, bristle-toothed and many cyprinids). On the inner surface of the scales adjacent to the body of the fish, there is a layer containing crystals of guanine and lime, which gives the fish a silvery color. The layer of guanine is especially abundant on the scales of pelagic fish (herring, sabrefish, bleak). The absence of guanine determines the transparency of the scales (smelt). The outer surface of the scales is covered with a layer of epidermis, under which there is a thin layer of connective tissue with pigment cells. On the body of some fish (carp, whitefish, smelt) during the spawning period, the so-called pearl rash appears on the body and head - tubercles formed by the growth of the epidermis, which cone-shaped extends outward. From above, the tubercle is covered with horny substance. Developing during the breeding season under the influence of sex hormones, the pearl rash later disappears, leaving no traces.

The body of some fish can be covered with bony shields, plates that perform a protective function. In some cases, shields or plates, tightly adjoining each other, form a shell on the body of the fish (sticklebacks, sea needles, boxfish, sea chanterelles).

Questions for self-examination:

What are the functions of the lateral line and sensory canals in fish?

What can be the sideline? Give examples.

How is the lateral line formula of fish drawn up?

What types of scales are found in fish?

What types of scales are the most ancient?

What fish have ganoid scales?

Name the types of bone scales and how they differ.

How does bone scale grow?

What relationship can be traced in the size of the scales and the nature of the movement of the fish?

What formations are found on the body of fish?

Who is the most famous aquatic inhabitant? Of course, fish. But without the scales, her life in the water would be almost impossible. Why? Find out from our article.

Why do fish need scales

Fish without scales practically do not exist. In some species, it covers the entire body from the head to the dorsal fin, in others it stretches parallel to the spine in separate stripes. If the scales are not visible at all, this means that it is reduced. It develops in the dermis, or corium of the skin, in the form of bone formations. This forms a dense protective cover. Examples of such fish are catfish, burbot, snake fishermen, sterlet, sturgeon and lamprey.

Chemical composition

Fish scales are the bony or cartilaginous derivatives of the skin. Half of its chemical elements are inorganic substances. These include mineral salts, namely phosphates and carbonates of alkaline earth metals. The remaining 50% are organic substances represented by connective tissue.

Types of fish scales

Performing the same functions, skin derivatives differ in their origin and chemical composition. Depending on this, several types of scales are distinguished. In representatives of the class Cartilaginous, it is placoid. This species is the most ancient in its origin. The skin of ray-finned fish is covered with ganoid scales. In bone, it looks like scales that overlap one another.

placoid scale

This type of fish scale has been found in fossil species. Among modern species, its owners are rays and sharks. These are diamond-shaped scales with a clearly visible spike that protrudes outward. Inside each such unit is a cavity. It is filled with connective tissue, permeated with blood vessels and neurons.

The placoid scale is very strong. In stingrays, it even turns into spines. It's all about its chemical composition, the basis of which is dentin. This substance is the basis of the plate. Outside, each scale is covered with a vitreous layer - vitrodentin. Such a plate is similar to the teeth of fish.

Ganoid and bone scales

Loop-finned fish are covered with ganoid scales. It is also located on the tail of sturgeons. These are thick rhombic plates. Such fish scales are interconnected with the help of special joints. Their combination can be a solid shell, scutes or bones on the skin. On the body, it is located in the form of rings.

This type of scale got its name from the main component - ganoin. This is a shiny substance that is a shiny layer of enamel-like dentin. It has significant hardness. Below is the bone. Thanks to this structure, placoid scales perform not only a protective function, but also serve as the basis of the muscles, giving the body elasticity.

Bone scales, which are monogenic in composition, are of two types. Cycloid covers the body of herring, carp and salmon. Its plates have a rounded rear edge. They overlap each other like tiles, forming two layers: cap and fibrous. Nutrient tubules are located in the center of each scale. They grow with a cap layer along the periphery, forming concentric strips - sclerites. From them you can determine the age of the fish.

On the plates of the ctenoid scale, which is also a type of bone scale, small spikes, or ridges, are located along the posterior edge. It is they who provide the hydrodynamic abilities of fish.

Long time no see...

Everyone knows that annual rings on the trunk can determine the age of a tree. There is also a way to determine the age of fish by scales. How is this possible?

Fish grow throughout their lives. In summer, the conditions are more favorable, since there is enough light, oxygen and food. Therefore, during this period, growth is more intense. And in winter, it slows down significantly or stops altogether. The activation of the metabolic process also causes the growth of scales. Its summer layer forms a dark ring, while its winter layer forms a white one. By counting them, you can determine the age of the fish.

The formation of new rings depends on a number of factors: fluctuations in temperature, amount of food, age and type of fish. Scientists have found that in young and mature individuals, rings form at different times of the year. For the first, it happens in the spring. Adult individuals at this time only accumulate substances by the summer period.

The period of formation of annual rings also depends on the species. For example, in young breams this happens in the spring, and in mature breams in the fall. It is also known that annual rings are also formed in tropical fish. And this is despite the fact that the seasons of the year, fluctuations in temperature and the amount of food are absent here. This proves that annual rings are the result of a combination of several factors: environmental conditions, metabolic processes, and humoral regulation in the body of fish.

Most most...

It would seem that what could be unusual in scales? In fact, many fish have unique characteristics. For example, coelacanth scales on the outside have a large number of bulges. This makes the fish look like a saw. No modern view has a similar structure.

A goldfish is called so because of the scales. In fact, this is a decorative form of silver carp. The first goldfish were bred in the 6th century in China by Buddhist monks. Now more than 50 breeds of this species are known with red, golden and yellow coloring.

At first glance, the eel is a fish without scales. In fact, it is so small that it is almost invisible. It is also difficult to feel it to the touch, as the skin of the eel secretes a large amount of mucus and is very slippery.

So, the scales of fish is a derivative of the skin. It is one of the features of the structure, which provides adaptation to life in the aquatic environment. Depending on the chemical composition, placoid, ganoid and bone scales are distinguished.

"Scaly world" - so we lovingly call the fish. But which of us has been more closely involved in these remarkable external signs of many fish, from pike to carp? Is the structure of scales in fish of all species the same? Are there fish without scales? What does scales tell us about fish and what is its role?

Based on the scientific definition, scales are the skin of most fish, which is formed in the subcutaneous layer and consists of bone plates. So, in any case, it is written in zoological books. The scales of our local fish have a complex structure. Basically, it consists of a transparent integumentary layer and an underlying bony layer of the base. It is reinforced with cartilage fibers and is characterized by so-called growth rings, which are interrupted in the radial direction so that the scales remain flexible.

There are different types of scales. We are primarily interested in large groups of round and comb scales. Shark placoid scales are not true scales. The so-called ganoid scale consists of a ganoid layer covered with bony plates, which is therefore not a true fish scale.

Characteristic features

In ichthyology, round scales are divided into six types.

1. herring scales(small, tender, easily separated).
2. Trout scales(small, round, without radial stripes).
3. carp scales(large, hard, from silvery to golden-shiny, in lines - small, inconspicuous).
4. pike scales(hard, typically folded).
5. acne scales(very small, buried deep in the skin, almost invisible).
6. Burbot scales(small, delicate).

The scales of some fish are formed so characteristically that they can be used to identify their owner. In the eructation of cormorants, for example, along with fish bones, undigested scales are encountered. Her research provides fairly accurate information about the food spectrum of fish-eating birds. The large, silvery, shiny scales of the “white” fish are noteworthy. In fish of some species, it is very thin and, like bleak, falls off very easily when touched. The scales of such fish, which have a silvery sheen, are used to make artificial pearls. Characteristic is the hard golden-shiny round scales of the carp or the large “mirror” scales of its breeding forms. The reticulated pattern of scales in the chub is an important identification feature of this species.

Ganoid scales are found in perch fish such as river perch, or walleye. It is small, firmly attached to the skin and has small teeth. The side of the scales sticking out from under the skin is jagged, so these fish seem rough to the touch. Round and ganoid scales form a tiled covering of the surface of the body of fish. Thanks to its ideal position, it does not impede the movement of fish when swimming and is also sufficient protection against damage. Under the scales is the integumentary skin. It contains mucous cells that form a smooth, closed mucous layer. If the scales are very small, like eels or tenches, the mucous layer is strengthened. Scaleless fish like catfish are very slimy. Their skin is tight. And the color cells are located here on top of the scaly layer. When the scales are removed, the fish lose their beautiful coloration, only the main tone under the skin, gray or green, remains.

Growth and regeneration

In summer, fish grow (and scales grow with them) faster than in winter, so that distinct annual rings form on the scales, which can be used to determine the age of the fish. By the time of spawning, growth slows down, which leaves traces on the scale rings. From an enlarged image of a single scale, experts can learn a lot about the life history of a fish.

Scale formation occurs in fish at a young age. The number of scales during her life remains the same. The scales grow evenly with the fish. The scales lost as a result of wounds are quickly restored. The newly formed scales grow very quickly, but often the harmonious original scaly appearance is no longer achieved. In the scar tissue of the skin, scales most often grow at random.

Some scales, especially those located along, are striking. There they have clearly visible openings, thanks to which the sense organs lying under the scales make contact with water. In fish of some species, similar scales are located outside the lateral line. Outwardly very similar cyprinids, such as the Danube roach and ide, whitefish (madder) or golden and silver carp can be accurately distinguished by the number of scales along their lateral line.

Scales in some areas also have a mystical meaning. Some people put a Christmas carp scale in their wallet every year so that it never gets empty.

fish scales- These are bone or cartilage formations located in the skin of fish.

The degree of development of scales in different fish is different, and in some fish (catfish, goby) a reduction has occurred.

The size of the scales can be varied in one family of fish and even in one species.

The structure of fish scales:

Placoid (it is very ancient);

ganoid;

Cycloid;

Ctenoid (the youngest).

placoid fish scale

placoid fish scale(photo above) is characteristic of modern and fossil cartilaginous fish - and these are sharks and rays. Each such scale has a plate and a spike sitting on it, the tip of which goes out through the epidermis. In this scale, the basis is dentin. The spike itself is covered with even harder enamel. The placoid scale inside has a cavity that is filled with pulp - pulp, it also has nerve endings.

Ganoid fish scale

Ganoid fish scale has the form of a rhombic plate and the scales are connected to each other, forming a dense shell on the fish. Each such scale is made of a very hard substance - the upper part is made of ganoin, and the lower part is made of bone. This type of scales have a large number of fossil fish, as well as the upper parts in the caudal fin in modern sturgeons.

Cycloid fish scale

Cycloid fish scale found in bony fish and does not have a layer of ganoin.

Ctenoid fish scale

Ctenoid fish scales also found in bony fish and does not have a layer of ganoin, it has spikes on the back. Usually the scales of these fish are tiled, and each scale is covered in front and on both sides by the same scales. It turns out that the back end of the scale comes out, but it is also lined with another scale from below, and this type of cover retains the flexibility and mobility of the fish. Annual rings on fish scales allow you to determine it