River crayfish: description, lifestyle, fishing methods, value and breeding

Appearance

The crayfish is a higher crayfish, an order of decapods that unites highly organized crayfish, as well as crabs and shrimp. In all representatives of this order, the body consists of a constant number of segments: there are 4 head segments, 8 thoracic segments and 6 abdominal segments.

If you look at the crayfish, you can easily notice that its body is made up of two parts: the cephalothorax (representing fused head and thoracic segments, the fusion seam is clearly visible from the back) and a segmented abdomen ending in a wide tail. The cephalothorax is hidden under a hard shell made of chitin, a polysaccharide, and in addition is covered with calcium carbonate, which increases its strength.

The shell is the skeleton of a crustacean. It performs a protective function; the internal organs of the crayfish are securely hidden under it, and the muscles of the arthropod are also attached to it. On its head there are two pairs of antennae or antennae, covered with bristles and very long, so the name “antennae” is more suitable for this organ. They perform the function of smell and touch, so crayfish can’t live without them. In addition, at their base there are organs of balance. The second pair of antennae is shorter in length than the first, and is needed only for touch.

There is a sharp spike on the front of the cephalothorax; on its sides, in recesses, there are black bulging eyes. They are located on long movable stalks, thanks to which the cancer can turn them in all directions. This helps the animal to clearly see the space around itself. The eye has a complex facet structure, that is, it consists of a large number of small ocelli (up to 3 thousand).

Claws are attached to the chest - these are the forelimbs. With them he protects himself from enemies, catches and holds the victim, and he also uses them to enter the female during the period of fertilization in order to detain her and turn her over on her back. From this it becomes clear that romance in intersexual relationships is alien to Cancers.

To move, the animal uses four pairs of long, walking legs. In addition, it has small legs that are located on the inner surface of the abdomen and are called abdominal legs. They perform a significant function by helping crayfish breathe. They are used by arthropod representatives to push oxygenated water to the gills. They are covered with a thin shell and located under the cephalothoracic shield, the latter creates a cavity for them.

Female and male - who is in front of us?

The female crayfish is significantly smaller in size than the male; she is more miniature and graceful in contrast to the male. The same can be said about the size of its claws - they are more modest in size. Its belly is noticeably wider than the first part of the body - the cephalothorax, whereas in the male it is narrower. And also a distinctive feature is the condition of two pairs of abdominal legs. In the female half of crayfish they are underdeveloped, while in the males they are well developed.

Their color depends on their habitat and water composition. The color of the crayfish blends with the bottom of the reservoir and “dissolves” among the stones and snags. Therefore, they are usually brown in color, brown with a greenish or bluish tint.

They grow up to 6-30 cm in length. But how long they live, there is still no exact answer to this question. Experts cannot determine their life expectancy. Some believe that crayfish live up to 10 years, others give them a much longer lifespan, talking about a 20-year life expectancy.

Description

Freshwater crayfish
Like all higher crustaceans, the crayfish has a developed, hard chitinous cover as its external skeleton. The color of crayfish covers is variable and largely depends on the habitat. Most often, crayfish are colored greenish-brown and brown, as well as blue-brown (“cobalt”). The body of the crayfish consists of a cephalothorax and a strong, segmented abdomen. Males are much larger than females, have a wider cephalothorax and larger claws. Crayfish breathe through gills. The circulatory system is of an open type (oxygen dissolved in water penetrates into the blood, and carbon dioxide accumulated in the blood is released through the gills into the water). Crayfish live on average about 8 years, but often live up to 10 years.

Area

Some crayfish prefer fresh water, while others require brackish water. Many representatives of these crustaceans live in crystal clear water. Therefore, if crayfish are found in a reservoir, then we can safely assume that everything is in order with the ecological situation in this place. But the narrow-toed species, which is less picky than its fellows about pollution, sometimes inhabits waters of low quality, which misleads people.

Crayfish need a sufficient concentration of oxygen in water and lime. If they are starved of oxygen, they die, and if there is a lack of lime, their growth slows down. They prefer a bottom that is muddy or contains little of it.

The temperature of the water affects their life activity, this is understandable - the warmer the water, the less dissolved oxygen it can hold, therefore, the gas concentration drops.

They settle at a depth of 1.5–3 meters, near the coastline, where they dig their minks. Crayfish of the same species usually live in a reservoir, but exceptions are rare when representatives of different species coexist in the lake.

Crayfish diseases

Most often, crayfish are affected by parasites, shell diseases, mycosis, plague, porcelain disease or rusty spot disease.

Parasites are most often introduced with snails and are treated with salt baths.

Shell disease can be caused by insufficient water hardness and low calcium content.

Plague is a contagious disease and most often cancer dies in convulsions. Plague can be recognized by the appearance of black, white or red spots on the shell or tail.

Kinds

There are 4 types of crayfish:

An endangered species is the thick-clawed crayfish , its numbers are so small that today it is on the verge of extinction.
They live in the adjacent territories of the Black, Caspian and Azov Seas in clean, brackish water. They cannot withstand sudden increases in water temperature. It should not rise above 22-26 °C. It grows up to 10 cm in length. Its body is colored brownish-green. The claws are blunt, slightly forked. A characteristic feature of the thick-clawed crayfish is a sharp notch on the stationary part of the claw, which is limited by cone-shaped tubercles. Does not live in polluted places.
The broad-toed species is found in many clean, fresh water bodies in the European part of the country. They can be found in any flowing body of water, where the water warms up to 22 °C in the summer months. This olive-brown or brown with a bluish tint grows up to 20 cm in length. Its claws are short and wide. It cannot be found in ponds with dirty water. Recently, its population has been declining and is under protection.
The narrow-clawed crayfish thrives in fresh and brackish water; it lives in the regions of the Black and Caspian Seas, slow-flowing rivers, and low-lying reservoirs. The length of its body reaches 16-18 cm, and thirty-centimeter specimens are also caught. The chitinous shell is brown in color - from light to dark. Its claws are very elongated - narrow and long. It is more resistant to pollution, so it can colonize polluted water bodies.
The American signal crayfish has spread to many water bodies in Europe, displacing other species. It was introduced to European countries after the population of local crayfish declined due to the “crawfish plague.” If we talk about Russia, its appearance was registered only in the Kaliningrad region.

Thick-clawed crayfish

Broad-fingered crayfish

Narrow-clawed crayfish

American signal crayfish

In appearance, the “American” looks like a broad-toed representative of crustaceans. A distinctive feature is a white or blue-green spot, which is located on the claw joint. It reaches a length of 6-9 cm, although some individuals can grow up to 18 cm. Their color is brown with a red or blue tint. It is resistant to crayfish plague, a mycotic disease from which crayfish die en masse, but is a carrier of infection.

External structure of crayfish

The body of the arthropod is covered with greenish-brown chitin, which protects the soft parts of the animal. The body consists of a massive cephalothorax and belly, which is narrow in males and wide in females. The head of the crayfish is cone-shaped, elongated, and ends with a sharp awl. It has movable eyes on both sides. A pair of short antennae act as organs of touch.

The olfactory organs are two long whiskers. The mouth opening is located at the bottom of the head, and at the top it is surrounded by the lip and jaws, which are necessary for digesting food. Crayfish have eight pairs of limbs. The front three are short jaws that help the arthropod feed. The rest are used for movement, three pairs of them with claws, which are the most important weapon. Thanks to them, the cancer defends itself or, conversely, attacks the victim.

Nutrition

Freshwater crayfish are omnivores, their diet is varied - it contains both plants and animals. For most of the season, their menu is dominated by food of plant origin. Of the plants he likes, he likes algae and the stems of water lilies, horsetail, pondweed, elodea, and water buckwheat. In winter they eat fallen leaves.

But for normal development they need food of animal origin. They love to eat snails, worms, plankton, larvae and water fleas. They do not disdain carrion, eating dead birds and animals at the bottom of the reservoir, hunting sick fish, that is, in their own way, they are orderlies of the aquatic ecosystem.

Crayfish do not kill their prey, nor do they inject poison into them to paralyze it. Like real hunters, they sit in ambush and instantly capture the unwary prey with their claws. Holding it tightly, they gradually bite off small pieces of it, so the crayfish’s lunch stretches out for a long time. Experts have also observed cases of cannibalism when there is a shortage of food in the reservoir or overpopulation.

After wintering, mating and molting, crayfish prefer food of animal origin, the rest of the time they feed on vegetation. This article describes feeding aquarium and pond crayfish.

Reproduction of crayfish

Like shrimp, females immediately after molting release special pheromones that are very attractive to males. The mating ritual of crayfish comes down to touching their mustaches and peculiar dances. When mating, the male turns the female onto her back and holds her with his claws.

Within 20 days after the peculiar dances, the female lays eggs. Just like shrimp, the female crayfish lays eggs under her abdomen and carries them with her until the crustaceans appear. The crustaceans become completely independent only after the second molt, when they stop hiding under the female’s abdomen.

For feeding small crustaceans, brine shrimp, chopped tubifex, or simply food that is usually used for fish fry are suitable.

Lifestyle

Crayfish are usually active in the dark or at dawn, but in cloudy weather they also get out of their burrows. These are hermits. Each arthropod lives in its own burrow, which is dug according to the size of its occupant. This helps to avoid the invasion of uninvited guests and penetration into the home of a relative or enemy.

During the day, they spend all their time in their shelters, closing the entrance hole with their claws. At the moment of danger, the crayfish move back and go deeper into the hole, some of which are up to 1.5 meters long. When they go in search of food, they do not go far from their home, moving along the bottom slowly, with their claws extended forward. If the prey is within reach, they act with lightning speed. He has the same quick reaction in moments of danger.

In summer, crayfish usually lives in shallow water areas, and with the onset of cold weather it moves to depth. Females overwinter separately from males, since at this time they bear eggs and hide in burrows. The male half of the crustacean “huddles”, gathering together several dozen individuals, overwintering in pits or burying itself in silt.

Places where you can find arthropods

Mastering the knowledge of where crayfish are found is a prerequisite for a rich catch. There is an opinion that they live in rivers with standing water, as well as in swamps. However, these arthropods prefer clean flowing water bodies with gentle currents.

In each of them there are areas that these animals have chosen for permanent residence:

Coastline with stones. This is the most attractive place for crayfish to be found, as they can live near the surface of the earth under cobblestones. They build burrows at the bottom of the reservoir and hide in them during the molting period.
Coast with cliffs. In cases where the depth in the river varies, and under the coastline can reach two meters, crayfish settle in these places. A prerequisite is the presence of peat or silt on the bottom surface of the reservoir.
Backwaters with snags are places where crayfish are found in large numbers. It is there that you can find quite large specimens.
Sandy bottom of the reservoir. In these places, hunting crayfish is very easy. There is little algae, the bottom is transparent and clearly visible. A successful hunt awaits everyone in these bodies of water.
Shell rock. The bottom dotted with them and the presence of areas with reeds indicate the presence of crayfish in these places.
Holes and holes in the ground. In places with steep banks, small holes with a diameter of about five centimeters can be observed. Crayfish live in them.
Banks in water. The presence of beer bottles and other containers in the water are places where crayfish are found, they hide in them. When fishing, you should check each of them.

Reproduction

Males are ready to reproduce when they reach 3 years of age; females reach puberty by 1 year longer. By this time, the crayfish grow up to 8 cm in length. Among sexually mature individuals, there are always 2-3 times more males than females.

Their mating occurs in the cold season and occurs in October - November. Dates may change due to weather or climatic conditions. A male can only fertilize 3-4 females. If for most representatives of the fauna this process usually occurs by mutual consent, then in the case of arthropods, mating resembles an act of violence.

Already in September, males noticeably become very active and show aggression towards individuals swimming past them. The male, seeing a female nearby, begins to pursue her and tries to grab her with his claws. That is why crayfish are much larger than females, since she can throw off a frail gentleman without much difficulty.

If the male managed to catch up with the female, then turning her over on her back, he transfers his spermatophores to her abdomen. Such forced fertilization sometimes ends in the death of the female, and the fertilized eggs die along with her. On the other hand, the male spends a lot of energy on the chase and practically does not eat during this period; often he simply eats the one who has caught the last female in order to strengthen his strength.

After 2 weeks, the fertilized female lays eggs, which are attached to the abdominal legs. She has a hard time all this time - she protects future offspring from enemies, provides the eggs with oxygen, and cleans them of silt, algae and mold. Most of the clutch dies; the female usually retains about 60 eggs. After 7 months, in June-July, crustaceans hatch from the eggs, only 2 mm in size and remain on the mother’s abdomen for 10-12 days. Then the crustaceans begin to swim freely, settling throughout the reservoir. At this point they reach a length of 10 mm and weigh about 24 g.

Features of behavior

The crayfish actively hunts mainly at night, and during the day it hides in a wide variety of natural shelters (float, stones, crevices, etc.). Artificial shelter for crayfish are holes dug or occupied by them, which are usually located along the coastline in soft soil or clay. The length of crustacean burrows reaches an average of 30-35 cm, and often reaches half a meter. In the summer, crayfish prefer shallow water areas of reservoirs, and in winter they prefer strong soil (clay, sand, etc.). Crayfish move in a peculiar way, that is, they move backward, but in case of danger they swim due to sharp and strong strokes of the caudal fin, like shrimp and some other crustaceans. Among crayfish, researchers often note cases of cannibalism, and this phenomenon mainly occurs with a sharp increase in population density or lack of food. In relationships between the sexes, male crayfish dominate, since they are larger than females, and in the event of conflicts between males, the larger and stronger crayfish usually wins.

Nutrition

In search of food, crayfish never move far from their burrows, and on average the distance they travel from the burrow ranges from 1 to 3 meters. The diet of crayfish is mainly dominated by plant foods (~90%) and some portion is occupied by animal foods (~10%). The plant food of crayfish includes a variety of algae and fresh aquatic or moisture-loving plants - nettle, water lily, horsetail, elodea, and pondweed. The range of animal food consumed by crayfish mainly includes a variety of mollusks, tadpoles, worms, insects and their larvae. The diet of animal food of crayfish also includes various types of carrion as a constant component of food - the corpses of animals and birds, which crayfish often eat clean. In winter, crayfish also feed on fallen tree leaves. According to the researchers' calculations, it was noticed that female crayfish consume more food, but eat less often than males.

Reproduction and development

Males of crayfish reach puberty 3 years after birth, and females 4 years. At the very beginning of autumn, male crayfish become much more active, mobile and even aggressive, and very often attack passing individuals. As soon as the male notices the female, he immediately attacks her and, grabbing her by the claws, turns her over onto her back. As a rule, the male must be much larger and stronger than the female, otherwise she will simply break out of his “embraces.” Having captured and turned over the female, the male transfers his spermatophores to her abdomen and then leaves her. It is estimated that a male crayfish is able to fertilize about 3-4 females in this way during the breeding season. Fertilized females then carry up to 200-250 eggs on their abdomen for 2 weeks. It has been noted that the incubation period for the development of fertilized eggs into young crustaceans largely depends on the water temperature. The breeding season for crayfish is October.

At the end of the development of the eggs, young crustaceans emerge from them, measuring about 2 mm in size. After the appearance of young crustaceans, they remain on the female’s abdomen for approximately another 10-12 days, and then, having left her, they proceed to independent feeding, development and settlement in the reservoir. Two weeks after birth, the size of the young crustacean reaches about 10 mm, and the weight is about 23-25 mg. It is known that in the first summer of their life, young crustaceans go through 5 stages of molting. At the same time, their length increases by 2 times, and their mass by 5.5-6 times. It has been noticed that the growth in size of young crayfish occurs quite unevenly, and depends on the temperature conditions of the water and the presence of a particular amount of food. Over the next year of life and development, the crustaceans go through another 6 stages of molting, and by the end of the year, the length of young crayfish reaches about 35 mm, and the weight often reaches 1.7-2 grams. By the fourth year of their life, crayfish reach a length of 90-95 mm, and from this point in time the number of molts decreases to twice a year.

Shedding

As mentioned above, a durable chitinous shell reliably protects the crayfish from the sharp teeth of the enemy, but on the other hand, it restrains its growth. However, nature has taken care of solving this problem, and it has the ability to periodically completely shed its old shell. Not only the chitinous coating of the cancer is renewed, but also the upper layer of the retina and gills, and part of the digestive tract.

In young crustaceans, already in the first summer, the shell changes up to 7 times; with age, the number of molts decreases and an adult gets by with one molt per season. The shell change occurs only in the summer, when the water in the lake or river warms up.

You should not think that this process of “rebirth” is easy and quick. It can last from a few minutes to a day. The arthropod first frees its claws with great difficulty, then the rest of its legs. Often, when molting, limbs or antennae break off, and the cancer lives for some time without them. Over time, the lost parts grow back, but have a different appearance. Therefore, crayfish fishermen often catch animals with claws of different sizes; one of them may have an ugly or underdeveloped shape.

Under the old “skin” before molting, a new soft cover has already formed until it hardens, and this will take about a month, sometimes more, the arthropod grows in length and is an ideal food for predatory fish and its larger relatives. And since he molts not in a shelter, but in an open space, he needs to get unharmed to his place of residence, where he sits out for up to 2 weeks without food, and waits until the cover more or less becomes keratinized.

Habitat and lifestyle

Cancers are more picky about their environment than many people think. The water where they live must be fresh; crayfish cannot reproduce in salt or salt-fresh sea water. Crayfish need the same oxygen content in water as salmon fish.

For normal life of crayfish in the warm season, the water should contain oxygen above 5 mg/l. Crayfish can live in both light and dark water, as long as it does not have too much acidity. The pH value of ideal water for crayfish should be above 6.5. The growth of crayfish in waters depleted of lime slows down. Crayfish are very sensitive to water pollution. If living conditions are favorable, then crayfish can live in a wide variety of fresh water bodies - lakes, rivers, oxbow lakes and streams. However, it seems that the favorite habitat of crayfish is still rivers.

In crayfish habitats, the bottom of the reservoir should be solid and free of silt. On a muddy bottom, as well as on rocky or sandy shores, as well as in shallow water with a flat, clean bottom, crayfish are not found, since they cannot find shelter for themselves or dig it out. Crayfish love rocky bottoms where they can easily find shelter, or bottoms suitable for digging holes. Crayfish burrows are found in coastal holes or on coastal slopes. Most often they are located on the border of a hard and soft bottom. The exit from the burrow, the corridor of which can be more than a meter long, is usually hidden under the trunk of a fallen tree, tree roots or under stones. A crayfish's burrow is quite narrow, dug according to the size of the inhabitant, which makes it easier for crayfish to organize protection from attacks by larger brothers. It is difficult to pull the crayfish out of the hole; it tenaciously clings to its walls with its limbs. That the hole is inhabited is indicated by fresh soil at the entrance. Cancer lives at a depth of 0.5 to 3.0 m. The best places for housing are captured by large males, less suitable ones are left for weak males and females. Juveniles stay in shallow water near the very shoreline, under stones, leaves and twigs.

Cancer by its way of life is a hermit. Each individual has some kind of shelter that protects it from its relatives. During daylight hours, the crayfish is in a shelter, closing the entrance with its claws. Sensing danger, he quickly backs away, going deeper into the hole. The crayfish comes out to search for food at dusk, and in cloudy weather - in the afternoon. It usually moves in the water at night with its claws extended forward and its tail held straight, but if startled it will quickly swim back with the help of strong tail strokes. It is usually believed that cancer stays in one place. However, after a few weeks, tagged crayfish end up in gear hundreds of meters from the places where they were tagged.

Height

The growth rate of crayfish depends primarily on the temperature and composition of the water, the availability of food and the density of crayfish in the reservoir. The growth rates of crayfish in different reservoirs are different. But even in one body of water it is not the same from year to year; much depends on the temperature of the water. In the first and second summers of life, males and females have the same growth rate, but at the end of the third summer, or second year of life, males are on average larger than females. In the conditions of southern Finland, crayfish reach a length of 1.4–2.2 cm by the end of the first summer, 2.5–4.0 cm by the end of the second summer, and 4.5–6.0 cm by the end of the third summer. Minimum Males reach the permitted size for fishing (10 cm) at 6-7 years of age, females at 1-8 years of age. In waters with sufficient food for crayfish and under other favorable conditions, crayfish can reach the size allowed for fishing two years earlier than the specified period, but under unfavorable conditions - several years later.

People often ask how big crayfish can grow. Fisheries advisor Brofeldt noted in 1911 that in the town of Kangasala there were specimens 16-17 cm long, although later such crayfish were caught less and less often. Suomalainen reported that the 12.5-13 cm long crayfish caught in 1908 were medium-sized specimens. These evidences seem like fairy tales to us - crayfish do not have to be so large. In 1951, the magazine Seura organized a competition to see who could catch the largest crayfish over the summer. The winner was a participant in the competition who caught a crayfish 17.5 cm long, 28.3 cm to the tip of the claw, weighing 165 g. The crayfish had only one claw, which explains its relatively low weight. It can be considered a surprise that the giant crayfish turned out to be a female. In second place was a male, whose length was 16.5 cm, and to the tips of the claws - 29.9 cm. This specimen weighed 225 g. Other examples of caught crayfish with a length of 17.0-17.5 cm are known from the literature. It is interesting to note that, according to the Estonian scientist Jarvekulgin, male crayfish over 16 cm long and weighing 150 g, and female crayfish over 12 cm long and weighing 80-85 g, are exceptionally rare. Obviously, the female caught in Finland in 1951 can be considered a giantess.

What about the age of the crayfish? How long do crayfish live? There is not yet a sufficiently accurate method for determining the age of crayfish, similar to how the age of fish is determined. The lifespan of crayfish individuals is forced to be determined by comparing age groups or groups of crayfish of the same length. Because of this, it is impossible to accurately determine the age of single large specimens. There is information in the literature about cancers reaching 20 years of age.

Shedding

Crayfish grow as if in leaps and bounds - as they replace their shells. Molting is an important moment in the life of crayfish; at this time, a thorough renewal of their organs occurs. In addition to the chitinous cover, both the upper layer of the retina and gills, as well as the protective upper layer of the oral appendages and parts of the digestive organs, are renewed. Before molting, the crayfish hides in its burrow for several days. But the molting itself occurs in an open place, and not in a hole. Replacing the shell only takes about 5-10 minutes. Then the defenseless cancer is huddled in a shelter for a week or two, while the shell hardens. At this time, he does not feed, does not move and, naturally, does not get caught in the gear.

Calcium salts enter the new shell from the blood and permeate it. Before molting, they accumulate in two oval solid formations located in the stomach of crayfish. Sometimes they can be detected when crayfish are eaten.

Molting occurs only in the warm season. In the first summer of life, the crayfish molts 4-7 times, depending on growth conditions, in the second summer - 3-4 times, in the third summer - 3 times and in the fourth summer - 2 times. Adult males molt 1-2 times a season, and females that have reached sexual maturity, as a rule, once. Closer to the northern border of the distribution of crayfish, some females molt every second year.

Molting of males, as well as females who do not have eggs under the tail, occurs at the end of June; females carrying eggs - only when the larvae emerge from the eggs and separate from the mother. In southern Finland, such females usually change their shells at the beginning of July, and in northern Finland their molting begins in August.

If the start of summer is cold, shedding may be delayed by several weeks. In such cases, when the fishing season begins (from July 21), the shell may not yet harden, and the crayfish will not be caught in the gear.

Reproduction

Male crayfish reach sexual maturity at approximately 6-7 cm, females at 8 cm. Sometimes there are females 7 cm long, carrying caviar under their tail. Males in Finland reach sexual maturity at 3-4 years (corresponding to 4-5 year seasons), and females at 4-6 years (corresponding to 5-7 year seasons).

The sexual maturity of a crayfish can be determined by carefully lifting its dorsal shell. In a male that has reached sexual maturity, curls of white tubes are visible in the tail part under the thin “skin”. The white color of the tubes, which are sometimes mistaken for parasites, is given by the liquid in them. Under the shell of the female, eggs are visible, which range from pale orange to brownish-red, depending on the degree of their development. The sexual maturity of the female can also be determined by the white veins running across the lower shell of the tail. These are mucous glands that secrete a substance with which the eggs are then attached to the tail limbs.

Mating of crayfish occurs in the fall, in September-October. Crayfish do not gather, like fish, to spawning grounds; their fertilization occurs in their usual habitats. The male uses large claws to turn the female onto her back and attaches spermatophores at the female's genital opening in the form of a white triangular spot. A few days later, or even weeks, the female, lying on her back, lays eggs. In Finnish conditions, the female usually lays from 50 to 150 eggs, and sometimes up to 400. The eggs are not separated from the female, but remain in a gelatinous mass secreted by her glands.

Under the female's tail, the eggs develop until the beginning of next summer. During the winter, the number of eggs is significantly reduced due to mechanical loss and fungal infection. In the southern part of Finland, the larvae emerge from the eggs in the first half of July, in the northern part of the country - in the second half of July, depending on the water temperature at the beginning of summer. When emerging from the eggs, the larvae are already 9-11 mm long and are very similar to small crayfish. But their back is more convex and relatively wide, and their tail and limbs are less developed than those of young crayfish. The larvae stay under the mother's tail for about 10 days until they completely suck out the transparent reddish yolk. After this, they separate from their mother and begin an independent life.

Nutrition

Cancer is an omnivore. It feeds on plants, bottom organisms, and even devours its relatives, especially those that are moulting or have just moulted and are therefore defenseless. But the main food is still plant food, or rather, in the first years of life, the crayfish feeds more on benthic organisms and gradually switches to plant food. The main food is insect larvae, especially mosquito larvae, and snails. Fledglings readily eat plankton, water fleas, etc.

The cancer does not kill or paralyze its prey, but, holding it with its claws, gnaws it, biting off piece by piece with the sharp parts of its mouth. A young crayfish can eat a mosquito larva several centimeters long for about two minutes.

There is an opinion that crayfish, eating eggs and fish, harms fisheries. But this information is based more on assumptions than facts. At the beginning of the current century, T. X. Yarvi pointed out that in those reservoirs where crayfish were released, the number of fish did not decrease, and in reservoirs in which the plague destroyed crayfish, the number of fish did not increase. Not a single one of the 1,300 crayfish from the two rivers caught by the research ate fish, although there was a lot of it and a wide variety of it. It's not that cancer can catch fish. Its slow movements are deceptive; it is able to quickly and accurately grab prey with its claws. The small portion of fish in the crayfish’s diet is apparently explained by the fact that fish simply do not swim close to the crayfish’s habitat. Cancer is certainly capable of eating sedentary, sick or wounded fish in large quantities and effectively clears the bottom of the reservoir of dead fish.

Enemies of crayfish

Crayfish has many enemies among fish and mammals, although it is well protected by its shell. Eel, burbot, perch and pike readily eat crayfish, especially during their molting. The eel, which can easily penetrate the crayfish burrow, is the most dangerous enemy of large individuals. For young crustaceans living in coastal waters, the most dangerous predator is perch. Larvae and juveniles of crayfish are also eaten by roach, bream and other fish that feed on bottom organisms.

Among mammals, the most famous enemies of crayfish are muskrat and mink. In the feeding areas of these animals, near the shores of reservoirs, you can find quite a lot of waste from their food - crustacean shells. And yet, what destroys crayfish the most is not fish and mammals, but the crayfish plague.

Catching and hunting crayfish

They catch crayfish all year round; they refuse to hunt them during the molting period, since the taste of the meat deteriorates. But this rule applies in those regions where it is quite common.

In some areas where the arthropod population is on the verge of extinction, fishing is completely prohibited, for example, in the Moscow region, or is allowed only during a certain period, as in the Kursk region. Usually, catching crayfish is prohibited during the period of fertilization and gestation of eggs by females.

When going for a catch, you need to find out what size and how many crayfish you can catch. Catching smaller arthropods may result in an administrative fine. The commercial size of crayfish, each region sets its own, but usually it is 9-10 cm.

Each country and each region may have its own standards for the production of crayfish that are allowed to be caught. Research the legality of this issue before you go catching crayfish!

How to catch?

There are 3 main and permitted methods of catching crayfish:

On the shoe . The method was invented a long time ago, but it is less effective. An old shoe, it is better to take a large one, is filled with bait and thrown to the bottom. They check it from time to time.
On a cancer fishing rod . The crayfish fishing rod has a simple structure. A fishing line is tied to a stick with a pointed end, which is stuck into the ground, and bait is tied to its end. Fresh fish or frog are used as bait. The bait is placed in a nylon stocking and a pinch of bloodworm is added. And to make the smell stronger, the fish should be “spread out”. The cancer clinging to the “victim” can be seen by the movement of the stick, fishing line, or felt by the shocks of the rod, which are carefully pulled out. However, the catch could be lost at any moment.
Using a crayfish. Crayfish have various designs of open or closed type and allow you to catch several pieces of crayfish at once. They are filled with bait and lowered to the bottom of the reservoir. Every 20 minutes they are raised and checked, after pulling out the catch, the crayfish is sent back to the bottom. It is more practical to use closed structures, since it is difficult for crayfish to crawl back out of them.
It is allowed to use up to 3 crayfish traps per person, with a mesh size of less than 22 mm and a device diameter of more than 80 cm.

Catching crayfish by hand, by diving (with or without scuba diving), or using a spear is prohibited by law.

When to catch?

Crayfish are best caught in the fall, when the water becomes cool and the days shorten, therefore increasing the hunting time, as they are caught in the dark or early at dawn. Select flowing reservoirs with a clay or rocky bottom, on the banks of which reeds, cattails or reeds grow.

How and when to catch crayfish is described in this article.

Catching crayfish

It is known that crayfish were caught already in ancient times. Until the Middle Ages they were used for medicinal purposes. It was recommended to sprinkle the ashes of live burnt crayfish on wounds from bites from rabid dogs, snakes and scorpions. Eating boiled crayfish was also prescribed for medicinal purposes, for example for exhaustion.

From historical literature it is known that at the royal court of Sweden already in the 16th century. gave a decent assessment of the taste of crayfish. Naturally, the nobles in Finland began to imitate the royal nobility. The peasants caught and supplied crayfish to the nobles, but they themselves treated the “shell-beast” with great distrust.

The crayfish fishing season in Finland begins on July 21 and lasts until the end of October. Starting from the second half of September, catches have been declining. In practice, crayfish fishing is stopped several weeks before the ban, since in late autumn the crayfish meat loses its taste and the shell becomes harder and harder.

Crayfish catches at the beginning of the season depend primarily on water temperature. If May and June are warm and the water temperature remains high, then the molting of both males and females ends before the onset of the fishing season. In this case, the catches are good from the very beginning. In cold summers, molting may be delayed, and crayfish begin to move after the shell hardens only at the end of July. As a rule, in the south of Finland the crayfish are always better caught at the beginning of the season than in the north, where the crayfish molt occurs later.

Chemical composition of cancer

Crayfish are caught for tasty, healthy and tender meat. The lion's share in it comes from proteins - 82%, fats - 12%, and carbohydrates - 6%. There are only 76 kcal in 100 g of edible part.

Meat contains many different vitamins: almost all representatives of group B, fat-soluble vitamins A and E, nicotinic and ascorbic acid. The mineral composition is also diverse - potassium, phosphorus, sodium, sulfur, calcium, magnesium, iodine and iron.

The benefits of crayfish meat are explained by the fact that the vitamins and minerals in it are balanced. Low calorie content and a lot of easily digestible protein make it indispensable for dietary nutrition. Experts also advise its use by people with cardiovascular diseases and liver diseases, with disorders of the nervous system and blood circulation. However, crayfish are strong allergens; if you are intolerant to the product, you should immediately discard it.

Spawning

Crayfish become sexually mature at the age of 3-4 years. Fertilization in crayfish is internal; due to the anatomical structure and aggressiveness of males, several conditions must be met for successful reproduction. First of all, the male must be larger than the female, otherwise the female may escape. Females are afraid of males and avoid contact with them, so males behave very aggressively and can be very rough on females. Large males copulate several times; after several fertilizations, the male, due to hunger, can devour the last female. After mating, females may not leave their burrows or shelters for a long time, fearing males, which disrupts the aeration of the eggs, and they may die. Three weeks after successful fertilization, spawning occurs. The eggs are attached to the female's pseudopods and will remain there until the larvae hatch. The larvae begin independent life only after two months.

Breeding

Crayfish farming is widely practiced throughout the world. Each country has its own technology for growing arthropods, but they all follow the rules:

the bottom of reservoirs with a small amount of silt;
It is necessary to have clean fresh water rich in oxygen;
compliance with temperature conditions;
compliance with the composition of the water.

One of the most economical breeding methods is considered to be pond breeding. It consists of setting up several ponds (usually 3-4 pieces), in which crustaceans are grown.

If you really want, crayfish can be grown at home - in an aquarium. The main thing is to find females with eggs that are attached to their abdomen. They are released into the water and the eggs are incubated; it is necessary to monitor water circulation and aeration of the water.

It is worth taking care of the food supply in advance. When the water is heated above 7 °C, the crustaceans are fed with boiled or fresh food, placing it on special trays.

Small crustaceans that have shed a second time are moved to the mother pond, and then sent to a new one or left in the same pond, provided that it is suitable for their wintering. Crayfish that are one year old are released into the feeding pond; here it is necessary to reduce the stocking density. They reach commercial size in the 2nd or 3rd year.

Population and species status

Photo: Broad-toed crayfish in nature

To track the change in the number of broad-clawed crayfish, you need to turn to history. Until the advent of the twentieth century, this crayfish was a numerous species, distributed throughout many fresh European water bodies. But everything changed starting in 1890, when one influential German, Max von dam Borne, brought about a hundred signal American crayfish to the United States, which he settled in the reservoir of his village.

These emigrants crossed the river into other bodies of water, where they settled firmly. American crayfish were carriers of crayfish plague; they themselves had immunity to this disease, which, unfortunately, was absent in broad-toed crayfish. The infection affected a huge number of river arthropods; they disappeared completely from many places. This situation has led to a large reduction in the population of broad-clawed crayfish.

Thus, from being a numerous species, the broad-toed crayfish has migrated to the category of the most vulnerable species. In many places it was replaced not only by its American counterpart, but also by the most unpretentious narrow-toed crayfish. Now the situation with the size of the crayfish population is also not very favorable; it continues to decline. This is due not only to disease, but also to massive fishing and the poor ecological situation in many water bodies, so the broad-toed crayfish needs special protection measures.

As already mentioned, the broad-toed crayfish is considered a small, vulnerable species, the population of which continues to decline, which causes concern among environmental organizations that are taking all possible measures to save it.

Various factors led to a strong decrease in the number of crayfish:

epidemic of crayfish plague;
displacement of the broad-clawed crayfish by other crayfish species that are unpretentious to external conditions;
mass fishing of crayfish for gastronomic purposes;
human pollution of water sources.

Interesting fact: It is recorded in writing that crayfish began to be eaten at the turn of the Middle Ages; among Swedish aristocrats, their meat was considered a great delicacy. Later, due to their abundance, crayfish became frequent guests on the tables of all segments of the population. Jews do not eat them because... they are considered non-kosher animals.

Crayfish protection

In the natural environment, due to the deterioration of the ecological situation, widespread pollution of water bodies and unlimited fishing, their numbers are declining every year. Of the crayfish, the thick-fingered species is on the verge of extinction, and the population of the broad-fingered species is also “striving” for this. They are listed in the Red Book of Ukraine and Belarus, and fishing with them is strictly prohibited.

Interesting Facts

There are several interesting facts about crayfish that you should know:

crayfish have blue blood;
in the true Olivier salad recipe, one of the ingredients was boiled crayfish, in the amount of 25 pieces;
Jews are forbidden to eat crayfish, as they are considered “non-kosher” food;
when cooked, all the pigments that are responsible for the color of the crayfish disintegrate, except for carotenoids, which is why after heat treatment it turns red;
Previously, it was believed that these arthropods were insensitive to pain, experts proved that this was not true; by boiling crayfish alive, people doomed them to a painful death;
The largest crayfish is caught on the island of Tasmania, its length is 60 cm.

In conclusion, it is worth noting that crayfish meat is rich in microelements that have a beneficial effect on the human body as a whole. However, it is not only healthy, but also tasty. That is why crayfish is one of the most popular representatives of arthropods.

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Variety of crayfish

Lobsters (sea crayfish)

American (Homarus americanus) and European (Homarus gammarus) lobsters are distinguished by an enlarged first pair of legs; in the Norwegian lobster (Nephrops norvegicus) they are longer and thinner. Usually one larger claw is the pressing claw; the other, smaller one is a cutting claw. The head has two pairs of antennae and a pair of compound eyes. The tail is fan-shaped. The female lays many thousands of eggs. Lobsters typically live up to 15 years, but one European record holder lived to 50.

Other crayfish families

Reef crayfish (genus Enoplometopus) live on coral reefs; their claws are only on the first pair of legs (in lobsters and crayfish, on the first three pairs). Glypheids consist of dozens of fossil species and two living species found in the Pacific Ocean.