Tips on how to determine the age of a fish. Children's experimental project “How to determine the age of a fish

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Everyone knows that the age of a tree can be accurately determined by the annual layers (rings), clearly visible in the cross-section. But only by cutting the root end of the trunk can one find out the true age of the tree. Using this, foresters learn both the age of individual trees and the average age of an entire group of trees. In mollusks, reptiles and other groups of animals, everything is spelled out exactly the same. In mammals - on teeth and bones, in birds - on bones, etc. In addition to the number of years lived, bones, teeth, trunks and other organs also carry more detailed information about many life parameters and even collisions (hunger and feeding periods, spawning, diseases, etc.). In livestock and crop production, foresters and livestock breeders actively use all this data when calculating plantings, planning herd numbers, and in many other cases.

It's the same with fish. Based on scales, it is possible to learn in detail the past of a given individual and even predict the near future. By using sclerite rings (summer and winter rings on the scales of cyprinids), a scientist can determine at what age a given fish becomes capable of reproduction, whether it is growing well, what age groups are found in the catch and which should be expected in the future. This is important because fish of a certain age are prohibited from being caught. From a research feasibility perspective, this is the easiest way to conduct an ecological analysis of any population.

Physiology of the occurrence of annual rings in fish

To correctly determine how old a fish is and what has happened to it over the years, it is necessary to understand the principle of formation of annual rings. If you look closely at the rings, you can see their alternation: wide light ones, followed by narrow dark ones, and so on. A wide light ring means that during the formation of this sclerite the fish was eating well and growing actively. That is, this happened in spring, summer or early autumn. Moreover, the most significant growth in the annual ring of all fish in our reservoirs begins in April. A narrow and dark ring is formed during the cold period, when there is no food. In some fish, in some years the winter rings are not visible at all.

Ring-sclerites arise in fish as a result of the fact that their scales and bones are capable of forming layers in the form of alternating rings, belts, planes and sclerites-ridges (or ridges). Each year of a fish's life corresponds to a specific ring on its scales or bones. Not all fish have an exact time for the appearance of scales on their bodies. In some, the first scales are noticeable 30-40 days after the larva emerges from the eggs, in others - much later. At first, the scale has the appearance of a thin transparent plate. About a year later, under the scale of the first year, a second, larger one grows, the outer edge of which protrudes beyond the edge of the first plate. In the third year, a third appears, etc. In an adult fish that is, for example, five years old, each scale consists of five plates (scales). This is somewhat reminiscent of a child’s pyramid: on top is the smallest scale, which is also the oldest plate, on the bottom is the largest, which is also the youngest.

How are sclerites formed?

As the fish grows, the size of its scales also increases. And since fish, depending on living conditions and physical condition, grow unevenly, scale growth also occurs unevenly, which either slows down or accelerates. This unevenness is reflected on the scales in the form of scars of varying thickness, ridges called sclerites (obviously from the Greek word “skleros” - hard, hard), which are arranged in circles or arches. The width of the sclerites is unequal, and the spaces between them are also unequal. When fish grow rapidly (in summer), more sclerites grow and the distance between them becomes wider. When the fish grows slowly, the sclerites are brought closer together. This happens in the fall. It is believed that sclerites do not form at all in winter. Bands of wide and narrow sclerites formed within one year constitute the annual growth ring. The number of such annual rings on the scales is the same age as the fish.

In addition to annual rings, there are additional rings on the scales that reflect periods of changes in fish growth throughout the year, depending on the nature of nutrition, water temperature, and spawning time. There is also a juvenile ring, which is often noticeable in the area of the first annual ring.

The shape and pattern of scales varies from fish to fish, so recognizing growth rings requires good observation and research skills. Of practical importance is the determination of the growth of fish for each year of its life, that is, the determination of the growth rate of the fish. The age and annual growth in length and weight of the fish can be determined quite accurately.

Where exactly is the age of the fish written?

It would be ideal to take large scales from a fish, blot them, hold them up to the light and after a couple of seconds proudly announce that this pike is already seven years old, that it has grown evenly, has not yet had time to spawn and now will not have time. And also find out that she was not sick with anything, did not go hungry and easily endured her six winters, so you can fearlessly eat her. But this is ideal. When you try to reproduce this on a pond, it turns out that all the scales are damaged, or small, or unreadable. An experienced fish farmer, of course, will say that the scales are simply wonderful and will quickly describe the characteristics of the life of a given individual. But what should less experienced anglers do? Let's start with the fact that all fish have different scales and are divided into several main types.

But how can one determine the age of a fish if it has no scales or if they are small and damaged? In this case, the so-called flat bones come to the rescue. First of all - auditory otoliths, gill covers, jaw bones, shoulder girdle, skull or bony skeleton of pectoral fins, sections of fin rays and other bone formations.

How can you see the annual rings of fish?

Now let's move on to practice. After acquiring a stable skill, you can determine the age of the fish with an accuracy of several months. Then, armed with some equipment, pen, paper and a calculator, it is possible to calculate many other vital parameters of the trophy. Find out how he grew up, ate, wintered, spawned, and whether he was sick or exposed to stress, how his infancy, childhood and adolescence went. If the fish is migratory, then you can find out how much time it spent in the river and how much time in the sea.

If you are going to conduct research on a pond, you need to take with you a magnifying glass with 8, 10, or even better, 20x magnification. Although any scientist will advise taking a portable binocular with you rather than a magnifying glass. You will also need a flat white surface, tweezers, a scalpel or a thin knife, ammonia or regular ethyl alcohol and a thick cloth. The part of the fish selected for research: scales, otolith or vertebrae must first be thoroughly cleaned of dirt, mucus, and blood. If the scales and vertebrae are very dirty, then you should put them in alcohol for five minutes, then wipe them, or better yet, blot them and dry them. It is best to remove 10-15 scales from the middle of the body of each fish, from the lateral line to the base of the dorsal or adipose fin. It is not recommended to take scales from the area of the lateral line and the bases of the fins, as they are difficult to see. Choose whole scales that are ideally shaped and characteristic of this species. If you are doing this at home, it is better to use a microscope if you have one. The so-called scaled eyepiece with divisions will help you calculate different parameters using the formula, with which you can calculate the absolute and relative width of different sclerites, and then use these numbers to obtain the necessary information about the age of the caught fish.

Dip the vertebrae, flat bones of the skull, auditory otolith pebbles, and gill covers selected for examination into boiling water for 3-5 minutes or rinse in diluted alcohol (gasoline, ammonia). Then wipe with a flannel cloth or soft brush, dry and make a thin cut. If one doesn't work out, do another. For such cases, always leave enough material to study. Annual rings are examined according to the same principle as on scales.

How is age calculated?

Scientists rarely say, “This carp is seven years old.” Having examined the scales or bones, they notice that there was more growth this year and derive a more accurate figure; 7+, that is, seven full years, and plus is the increase in the last year. If you caught carp in winter or spring, you will get a whole number. And call it correctly - seven-year-old (or two-year-old, three-year-old, etc.). And if you catch the same carp in summer or autumn, then a plus is added, and this carp is correctly called “seven-year-old”. And other fish caught during this period will be fingerlings, one-year-olds, two-year-olds, three-year-olds, etc. Be careful, because fish that have survived prolonged hunger and cold develop another small ring, so you can miscalculate. If the scales are clear, and you have the device and necessary tools at hand, you will be able to learn a lot of interesting things about the trophy. Using simple formulas, you can calculate what size a three-year-old pike perch was last winter or the summer before last. The Scandinavian scientist Einar Lea, who proposed one of these formulas, studied the age and growth rate of Norwegian herring and came to the conclusion that the growth of scales is proportional to the growth of the fish, that is, the annual increase in scales is also related to the length of the scales, as the annual increase in body length is to the total length bodies. For example, if it is found that in a certain year the scales have grown by 1/10 of the entire length of the scales taken, then we can assume that over the same year the fish’s increase in length was also 1/10 of its body length. That is, by determining the ratio of annual scale growth for each year, you can determine the body length of the fish in each year it lives. Based on the scales, one can also determine what happened with spawning in a given individual. In many fish, during spawning, the edges of the scales break off, become deformed, and an uneven ring is obtained. By counting the crooked rings, it will become clear how many times this fish has spawned in its life.

Next, we will explore favorable and unfavorable periods in the life of a trophy. The fish grows throughout its life, but unevenly. In winter it hardly grows, but even in spring and summer its growth can be uneven. In feeding and warm years it grows intensively, so its sclerite is wide and light. And in a hungry spring the sclerite is narrower and darker.

Sometimes you can see several light rings in a row. This most often occurs when the dark ring is so narrow that it cannot be detected by the eye. Based on the exact size of these rings, using simple formulas, you can calculate what size (height and weight) the fish had in the summer of the year before last or in the winter five years ago.

The work of Russian scientists played a significant role in the development of methods for studying the age of fish. Works by V.K. Soldatov on studying the age composition of Amur sturgeons based on bones, studies by I.N. Arnold, N.L. Chugunov, E.K. Suvorov, G.N. Monastyrsky, N.I. Chugunova and others. They gave a lot both for the theoretical development of the issue and in the direct application of the method to solve practical problems.

The great importance of determining the age of fish for resolving fishery issues has led to the fact that recently a lot of material has accumulated in this area, both in foreign and Soviet literature, and there are many methodologically interesting studies (review of methods for determining age and rate fish growth is given in the book by N.I. Chugunova, 1959).

The main object for age determination Most fish have scales.

Collecting scales is simple. The scales are easily processed and in many species of fish - almost all salmon, herring, carp, cod and others - allow one to reliably determine age. Scales used for age determination fish, is usually taken under the base of the first dorsal fin and placed between sheets of notepad made of unglued paper; on the page on which the scales were placed, data is recorded about the fish specimen from which the scales were taken (length, weight, sex, place of capture, fishing gear, etc.). To determine the age, the scales, previously washed in a weak solution of ammonia, are placed between two glass slides and viewed under a magnifying glass or microscope, depending on their size. Delicate scales, such as those of cod, are sometimes best placed in glycerin-gelatin. It is not recommended to put scales into Canada balsam to determine age, because it becomes very bright and the annual rings become difficult to see.

In perch, burbot and some other fish, flat bones, such as the operculum and cleithrum, are good objects for determining age. The visibility of the growth layers on bones is often no less distinct than on scales. The most reliable is to determine the age of the same fish, simultaneously carried out using both scales and bones, which serve as good control material. The method of preparing bones to determine age is very simple: the bone is cleared of meat, degreased and dried. As a rule, it is impossible to determine age based on bones collected from rotten fish or those lying in formaldehyde, since such bones usually become cloudy.

In cod and flounder, age determination is often made by otoliths - ear stones (Fig. 88), which are removed from the skull by opening the labyrinth. To determine age, otoliths must be degreased and, in some cases, slightly polished to make them more transparent. Relatively large otoliths (at least 0.5) are usually broken transversely, the otolith is inserted with its pointed end into a piece of wax or black plasticine with the break pointing upward and, moistened with a clearing liquid (xylene, transformer oil, etc.), examined with the necessary magnification.

In sturgeons, catfish and some sharks (Acanthias), age is determined by the fin ray: in sharks - gypsy, in sturgeons and catfish - pectoral. Moreover, in sharks, rings are visible on the fin ray immediately after cleaning the ray; in sturgeon and catfish, it is first necessary to prepare a cross section of this ray, which is polished until transparent, and then glued to a glass slide with Canadian balsam, and in this form can be used to determine age. To prepare sections, a special machine has been designed, consisting of two parallel machines; fixed round files driven by an electric motor. By adjusting the distance between the files, you can make cuts of varying thickness. Beam cuts can also be made using a regular jigsaw with metal files or an electric jigsaw.

Since the formation of the annual mark occurs as a result of changes in the growth rate, the question naturally arises whether “annual rings” could form several times a year, not only as a result of cessation of nutrition in winter, but also as a result, for example, of a hunger strike in winter. the time of spawning, transition from one type of food to another, more nutritious, etc. The main method of determining whether the number of rings on the scales corresponds to the age of the fish is to study the scales of fish whose age is known, or fish that have lived a certain time after their the first time scales were taken. As shown by the study of fish living for a certain number of years in ponds and aquariums, as well as the capture of fish previously tagged in open water bodies (salmon, cod, roach), the number of rings on the scales and layers on the bones corresponds, as a rule, to the number of years lived by the fish . True, sometimes additional rings do appear on scales and bones, the appearance of which is often natural and associated with a certain moment in the life of the fish. So, for example, some fish (dace, roach, etc.) have a so-called fry ring inside the first year ring, which is associated with the moment of transition of the juveniles from feeding on plankton to feeding on bottom organisms.

Often the accessory rings are not expressed in a circle, but only on one side of the scales, which makes them easy to distinguish from annual ones.

Many fish have spawning rings and marks on their scales, which are the result of cessation of feeding and exhaustion during spawning.

Spawning marks are of two types: Type I is observed in Atlantic and Caspian herring and salmon. It is formed by destruction of mainly the lateral sides of the scales and their subsequent restoration. Type II is observed in roach, bream and some other fish. It is formed in those species in which spawning weight loss is less pronounced. Destruction of the scales does not occur during spawning, only a slight change in the structure of the sclerites is observed, a “dark” sclerite or omission of sclerite is formed, and in its place a white shiny strip appears. Spawning marks in males are more clearly expressed than in females (especially salmon). Quite often they coincide with annual rings. For example, during spawning, the scales of Caspian herring begin to deteriorate, which leads to the formation of a certain deep mark on it. In salmonids, spawning marks are also clearly visible on the scales, having the shape of rings, but of a slightly different nature than annual ones. Moreover, in male salmon S"almo salar L. spawning marks are usually more clearly expressed than in females.

In the Cassius roach, by studying the scales of marked and re-caught fish, in addition to spawning and fry, three more types of additional spots were established, namely the 1st type, which appears when the growth of the fish is accidentally delayed, the 2nd type, which appears in case of change the nature of scale growth, and the 3rd type, formed along the break line on scales that regenerate after mechanical damage.

The formation of annual and additional rings, as well as spawning marks, on the scales of fish is an adaptation that makes it possible to maintain the correspondence of the scale cover with the body shape that changes as a result of weight loss; Since the scales usually overlap each other in a tiled manner, the correspondence between changes in the shape of the body and the scale cover is achieved to a large extent due to the sliding of one scale over another. The rings and markings on the anterior and posterior edges of the scales are less clearly defined than on the sides, where the scales are adjacent to each other without overlapping and where, for example, during spawning, the greatest destruction of the scales takes place.

Naturally, the question arises whether the presence of additional rings on the scales, bones and otoliths of fish does not make the entire method of determining age using annual marks generally flawed, and what are the methods for distinguishing annual rings from additional ones?

Rice. 89. Scales of a three-year-old carp, treated with chloral hydrate and divided into plates corresponding to individual years of growth

nykh. A lot of work has been done to resolve this issue. In particular, V.V. Petrov and G.K. Petrushevsky (1929) tried to macerate carp scales and divide them into separate plates, each corresponding to a specific year of growth (Fig. 89). O. Vinge (1915) measured the width of individual sclerites on cod scales and plotted these values on graphs. From the number of apexes corresponding to the size of the widest sclerites, he obtained the number of annual rings; Although the additional rings gave some change in the size of the sclerites, it was less significant than the annual ones. Usually, to check the correctness of age determination, they use not just one object, but several, for example, if the determination is made by scales, then from some control specimens, in addition to scales, the bones of the gill cover are taken.

Along with the study of rings on scales and bones, it is also absolutely necessary to study the lifestyle of fish to identify patterns of its growth that could affect the growth of scales.

Knowing the moments in the life of a fish that can affect the growth of scales will allow, if there are corresponding rings on the scales, to treat them with great caution and it will be easier to identify their nature. The greatest difficulty is recognizing the fry ring. Usually, in order not to confuse the fry ring with the first annual, in the fall several samples of fry of the species under study are taken, analysis of the size of which makes it possible to establish with certainty which ring we were dealing with - an annual or a fry. In general, as a rule, additional rings and marks of all types are less pronounced than annual ones, and with some skill they can usually be identified without much difficulty.

We examined cases when the number of zones on scales and bones is greater than the number years, lived by the fish, but it may also be that the number of rings on the scales and marks on the bones, on the contrary, is less than the number of years lived by the fish. This question is of particular importance when determining age by scales. Regenerated scales have fewer annual rings than normal scales. In addition, in some fish, such as the eel, scales are formed only in the third or fourth year of life, and, naturally, the number of annual rings on the scales is obviously less than the number of years the fish has lived and the number of marks on the bones.

As can be seen from the above, the listed deviations from the norm in no way reduce the overall value of the method of determining the age of fish by scales and bones. When using this method, all that is required is a careful analysis of the nature of the rings and an individual approach to each object being studied, and most importantly, taking into account the specific features of the ecology of the fish.

There are many professions in the world directly related to the breeding and research of various types of fish. Knowing the age of an individual, you can detect any diseases and other deviations from the norm. This is why it is important to know how to determine the age of a fish.

Ways to calculate how old a fish is

There are several ways to do this:

Examine scales
Examine the bones
Study external signs (color, etc.)

How to determine age by examining scales

Perhaps the most universal way to determine the age of a fish is scale analysis. To do this, you will need a microscope or magnifying glass that provides tenfold magnification.

Such an analysis can be compared to determining the age of a tree by its growth rings, but when examining fish, it is not necessary to saw it. When looking at the scales, you can notice small rings. Each of them is equal to one year. Very often they are called winter, despite the fact that they can appear at other times of the year, for example, in spring or summer. The habitat does not affect their appearance, so the age of any individual, be it river or sea, can be determined in this way.

Using magnifying devices It is also possible to determine the size of an individual in different years of its life. Let's imagine a fish one meter long with a scale radius of one centimeter. Let's say the segment running from the first ring to the center of the scales is six millimeters. Thus, it can be understood that at the age of one year the length of the fish was sixty centimeters.

Thanks to this you can also see rates of growth. If rings are close to each other - the fish grew slowly during this period of time. This also allows you to determine the presence of any diseases that have affected growth. Growth rates can also indicate how well the individual ate.

Identification by bones and cartilage

Thanks to the rapid development of ichthyology, scientists have managed to dispel many legends about giant, long-lived fish. For example, one of the most popular tales among scientists and fishermen was the story of a pike that allegedly lived for more than two hundred years and weighed about one hundred and thirty kilograms. Her skeleton was even displayed at scientific exhibitions. A more detailed study showed that in fact the skeleton was assembled from the bones of two representatives of the pike species. The purpose of the deception was to make a profit.

This is why it is necessary to have other options in stock for determining the life length of a fish. In a situation where determining age by scales is impossible, several other methods can serve as a solution. For example, conduct a study of auditory pebbles and gill cover.

Even if only bones remain, the number of years she lived can still be known. For each year that the fish swims, a stripe appears on its gill covers. In cartilaginous species They also have their own annual rings. They are located on the rays at the base of the pectoral fins.

The lifespan of some species can be determined by cutting the otoliths. They are durable formations that appear at places experiencing mechanical irritation. At the cut site, all the rings are very clearly visible.

How to determine the age of an aquarium fish

A farmer who personally breeds fish is unlikely to encounter problems when determining age. In the end, it is he who must monitor their birth. As for aquarium fish, the situation is much more complicated. It is impossible to determine age by eye - scales are too small. Coloring and size are also not very suitable, since they are greatly influenced by environmental conditions such as temperature, food and much more. The following signs are characteristic of old fish:

Dull scales;
Lethargy;
Weak appetite
Reduced movement speed.

However, even these signs may indicate a completely different cause - illness. Over time, the color may become bright again, and the fish itself will return to its former prowess and appetite.

It is extremely important for ichthyologists to know the exact answer to the question “ how to find out the age of a fish" Knowing it, you can make many different predictions. For example, when to expect a population increase (many species reproduce every few years). For particularly interesting samples, for example, those who is listed in the Red Book, scientists have been observing for years to determine exactly when the fish will lay eggs.

It is especially difficult to say something about the age of long-lived species, of which there are many in nature. For example, the above pike can live up to ninety years. Another good example is Kamchatka perch. The life record of this giant reached one hundred and forty years. There are also many rumors about catfish. It is rumored that they can live more than a hundred years, but in fact there has never been an individual who has lived more than forty.

The age of a fish is reflected not only on its scales, but also on all its bones - “documents” that are stronger than scales. After all, there are fish without scales. Many catfish do not have scales. Some gobies also have no scales. In sharks, rays and other lower fish, instead of ordinary scales, the body is covered with plates with teeth (such plates are called placoid scales). In sturgeon fish, scales are replaced by five longitudinal rows of strong cone-shaped spines - bugs.

They have not yet learned to determine the age of fish from shark plates and sturgeon bugs, since the annual rings are not visible on them. But sturgeon fish have bones in their heads (as strong as those of bony fish), on which annual rings or planes are visible, which make it possible to determine the age of the fish.

Ichthyologists have found that the cuts in the rays of the fins also have annual stripes, and from them the age of the fish can be determined.

If the fish has a bony spine, then the age can be easily determined by the vertebrae.

Finally, the age of fish is also determined by otoliths - calcareous stones located in the auditory capsule of fish.

A long time ago it was noticed that there are stripes on the bones of fish. These stripes were sketched and reproduced in ancient books, but for a long time no one thought of linking these stripes with the age of fish. Only at the beginning of this century did they begin to study the age of fish from bones. The bones of flounder, cod and other commercial fish of the North and Baltic seas were studied, as a result of which they came to the conclusion that it is more convenient to determine age by flat bones similar to plates. Russian scientists E.K. Suvorov, V.K. Soldatov, V.O. Kler and others worked a lot in this direction.

If you remove the skin or muscles from the gill bones, slightly cook the bones and clean them with a toothbrush, then the annual stripes will be visible even with the naked eye. When viewed through a magnifying glass (5-10 times magnification), they are visible even more clearly. The picture shows two gill bones of a roach: on the left - the subopercular, on the right - the operculum. Both have 8 growth stripes and one narrow strip along the outer edge of the bones. Age - ninth year. The lower end of the gill operculum is thick and the first annual ring is difficult to find. The bones of the shoulder girdle and collarbone are removed through the gill openings, but this operation must be done carefully so that they remain intact. On bones, annual stripes are usually clearly visible, but in large fish older than 10 years, the first annual stripes (one or two) are often barely noticeable.

To determine age, vertebrae are ground vertically.

Ichthyologists have learned to determine the age of fish not only by flat thin bones, but also by bones that have a compact structure. A strong, thick ray of the pectoral fin of sturgeon or catfish is taken and an incision is made at its base. Then a plate is cut out, on which, after grinding, the annual planes can be found. The figure shows such a plate from a cut of the ray of the pectoral fin of a sterlet. 10 stripes are clearly visible - the sterlet was 10 years old.

Annual stripes are visible on sections of the rays of many, probably all fish. The age of cod can be easily determined by the rays of the dorsal fin; the age of catfish, whitefish, asp and other fish - by the rays of the pectoral fin.

However, it is not yet known how to determine the age of lampreys. This animal is very special: it has neither gill covers nor vertebrae, and the rays of its fins are completely soft. However, over time, ichthyologists will learn to determine the age of such fish. Ichthyological science is penetrating deeper and deeper into the secrets of the life of fish. If it is impossible to determine the age of a lamprey by its body structure, then direct observations of it in nature and in an aquarium must be used for this purpose.

This is a very interesting question that worries many anglers. Although, on the other hand, this is not entirely important if there are no restrictions on fishing. Some of them determine the approximate age of the fish by size. But the size and weight of the fish may depend on a number of factors, including the availability of food in the reservoir. Therefore, this approach gives only approximate results, although quite satisfactory.

There is another way by which you can find out a more accurate age of a fish, just as you can calculate the age of a tree from a cut using its annual rings. You can find out about this by the scales, if you look at them carefully, by the bones and gills. Specialists involved in this field know almost everything about fish: what age they are, how intensively they grew, how many times they spawned, etc. In other words, fish scales are like a business card, or more precisely, like a passport.

If you look at the scales with a microscope, you can see peculiar rings on it, very similar to those observed on a cut of a tree. Each ring is a witness to another year lived. Based on the scales, it is possible to determine both the age of the fish and its length by which it has grown over the previous year.

Specimens up to 1 meter long have scales with a radius of up to 1 centimeter. The distance from the annual ring (initial) to the central part of the scale is about 6 mm. Using this information, it can be determined that the fish has grown by 60 cm over the year.

If you look at the scales under a microscope, you will notice another, but very important feature - the unevenness of the surface. On the scales you can see ridges and depressions, which are also called sclerites. Over the course of one year of life, 2 layers of sclerites appear - large and small. A large sclerite indicates a period of active growth of the fish, and a small one indicates that the fish has experienced the autumn-winter period.

If you accurately determine the number of double sclerites, you can simply determine the age of the fish. But, even in this case, you need to have certain skills.

But this is not a problem if the fish has large scales. At the same time, there are species of fish that have rather small scales and this method is not suitable, since it is not possible to calculate how long the fish lived. That is, it is possible to calculate it, but this will require special equipment. In this case, to calculate the age of the fish, the skeleton is taken as a basis. Based on this, we can conclude that it is not at all easy for an ordinary person to cope with this task, since the process requires special tools.

How do annual rings appear in fish?

To correctly and accurately determine the age of a fish, it is necessary to know the physiology of growth of annual rings.

If you look closely, you will notice that the rings are distributed in certain stages: after the wide and light rings there are narrow and dark rings. A wide ring indicates moments when the fish was actively growing and developing. As a rule, this is spring, summer and autumn. The dark ring forms when the fish is in cold water and with little to no food. Sometimes it is difficult to identify dark rings on fish, which indicates difficult wintering conditions.

Such rings are formed because the bones of the fish and its scales are endowed with such a feature as the appearance of layers, depending on living conditions. On the other hand, uniform development of scales or skeleton is only possible if the fish is in ideal conditions, which never happens.

Each year of a fish's life does not remain unmarked on the scales or fish bones. At first, the scale consists of a transparent plate. A year later, a second plate forms under it, which extends beyond the edge of the first. Then the third, then the fourth, etc. If the fish is about 5 years old, then its scales consist of 5 plates, one after the other. This arrangement is reminiscent of a layer cake, when the smallest but oldest plate is on top, and the largest but youngest plate is below.

How can you see the annual rings of fish?

It is very problematic to count or detect annual rings in fish, especially with the naked eye. Therefore, you need to have a magnifying glass or binoculars if everything happens on a pond. If you decide to deal with this problem at home, then it is better to arm yourself with a microscope. Before the process itself you need:

Prepare the scales for inspection and, if necessary, wash them with alcohol.
For inspection, it is better to take the largest scales, which are located on the sides.
The scale should not have mechanical damage.

For more accurate calculations, it is necessary to take into account the absolute and relative size of sclerites. Under a microscope, annual rings, ridges and depressions will be visible. After several such approaches, it is possible to determine the age of the fish realistically and with great accuracy.

How is the age of a fish calculated?

Using scales and bones, you can determine with some accuracy the age of the fish or its growth a year earlier. To do this you will need a microscope and some tools. Based on the state of the scales, it is possible to determine what happened to the fish during spawning periods, for example. In some species of fish, when they go to spawn, their scales break off. Based on this factor, you can determine how many times the fish has already spawned in its life.

It is always easier to determine the age of a fish if it has thin but long scales. Thus, it is much easier to determine the age of pike, taimen, grayling, herring and many other species of fish.

It is much more difficult to determine the age of perch, burbot or eel. In this case, you will have to take flat bones as a sample. The age of sturgeon is determined by the large rays of the dorsal fins. To do this, take the largest beam and cut it at its widest point. Then the cut area is polished until transparent, after which the annual rings can be seen. After this, the age is calculated using the generally accepted method, which is applied to scales. This approach is used to determine the age of other fish species, such as catfish.

In addition to these methods, there is another method, which is based on the study of gills. Marks similar to those on the scales remain on the gill covers after each year. Scientists have determined that even fish that do not have a skeleton have their own annual rings. Such rings are formed on the thick rays of the pectoral fins.

To determine the abundance of a particular fish species, it is necessary to understand how dynamically a particular fish species develops. There are species that spawn quite late. If you take Amur salmon, they only begin to spawn at the age of 20. And so, if you go through individual species, you can understand that each species develops absolutely independently of one another and each species lives for a certain period of time. It is very important for science to know how long a particular species of fish can live in order to control the populations of certain species of fish. As for fishermen, for them the approximate age of the fish does not mean anything significant.