Green crayfish. Biology: external and internal structure of crayfish. Female and male - who is in front of us

Crayfish / Astacus fluviatilis

These are the organs of touch and smell. The structure of the eyes is complex, mosaic (they consist of separate eyes united together). Modified limbs are located on the sides of the mouth: the front pair is called the upper jaws, the second and third - the lower. The next five pairs of thoracic single-branched limbs, of which the first pair are claws, the remaining four pairs are walking legs. Crayfish use claws for defense and attack.
The abdomen of cancer consists of seven segments, has five pairs of biramous limbs that serve for swimming. The sixth pair of abdominal legs, together with the seventh abdominal segment, forms the caudal fin. Males are larger than females, have more powerful claws, and in females, the segments of the abdomen are noticeably wider than the cephalothorax. When a limb is lost, a new one grows after the molt.
The stomach consists of two sections: in the first, food is ground with chitinous teeth, and in the second, crushed food is filtered. Further, the food enters the intestines, and then to the digestive gland, where it is digested and absorbed. Undigested residues are excreted through anus located on the middle lobe of the caudal fin. Circulatory system in crayfish it is not closed.
Oxygen dissolved in water penetrates through the gills into the blood, and carbon dioxide accumulated in the blood is excreted through the gills. Nervous system consists of the peripharyngeal nerve ring and the ventral nerve cord.

Color: varies, depending on the properties of the water and habitat. Most often, the color is greenish-brown, brownish-greenish or blue-brown.

Size: males - up to 20 cm, females - somewhat smaller.

Lifespan: 8-10 years.

Habitat: fresh pure water: rivers, lakes, ponds, fast or flowing streams (3-5 m deep and with depressions up to 7-12 m). In summer, the water should warm up to 16-22 "C.

Food / food: vegetable (up to 90%) and meat (mollusks, worms, insects and their larvae, tadpoles) food. In summer, crayfish feeds on algae and fresh aquatic plants(weed, elodea, nettle, water lily, horsetail), in winter - fallen leaves. At one meal, the female eats more than the male, but she also eats less often. The crayfish looks for food without moving far from the hole, but if there is not enough food, it can migrate 100-250 m.

Behavior: crayfish hunt at night. During the day, it hides in shelters (under stones, tree roots, in burrows or any objects lying on the bottom), which protects it from other crayfish. It digs holes, the length of which can reach 35 cm. In summer it lives in shallow water, in winter it moves to a depth where the soil is strong, clay or sandy. There are cases of cannibalism. Creeps, crayfish, moving backwards. In case of danger, with the help of the caudal fin, it stirs up silt and swims away with a sharp movement. In conflict situations between a male and a female, the male always dominates. If two males met, then the larger one usually wins.

Reproduction: in early autumn, the male becomes more aggressive and mobile, attacks the approaching individual even from the hole. Seeing the female, he starts the pursuit, and if he catches up, he grabs her by the claws and turns her over. The male must be larger than the female, otherwise she may break out. The male transfers the spermatophores to the female's abdomen and leaves her. In one season, he can fertilize up to three females. After about two weeks, the female spawns 20-200 eggs, which she carries on her abdomen.

Season / breeding season: October.

Puberty: males - 3 years, females - 4.

Pregnancy/incubation: dependent on water temperature.

Offspring: newborn crustaceans reach a length of up to 2 mm. For the first 10-12 days they remain under the belly of the female, and then move on to independent existence. At this age, their length is about 10 mm, weight 20-25 mg. In the first summer, the crustaceans molt five times, their length doubles, and their weight six times. The next year they will grow to 3.5 cm and weigh about 1.7 g, shedding six times during this time. The growth of young crayfish occurs unevenly. In the fourth year of life, crayfish grow to about 9 cm, from that moment they molt twice a year. The number and timing of molts are highly dependent on temperature and nutrition.

Benefit / harm to humans: crayfish is eaten.

Crayfish

Like all higher crustaceans, crayfish has a developed, hard chitinous cover as an external skeleton. The color of the integument of crayfish is variable, and largely depends on the habitat. Most often, crayfish are greenish-brown and brown tones, as well as blue-brown ("cobalt"). The body of cancer consists of a cephalothorax and a strong jointed abdomen. Males are much larger than females, have a wider cephalothorax and larger claws. The breath of crayfish is gill. The circulatory system is of an open type (oxygen dissolved in water enters the blood, and carbon dioxide accumulated in the blood is excreted through the gills into the water). Crayfish live on average for about 8 years, but often live up to 10 years.
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Head (front)

The cephalothorax of cancer consists of the head (anterior) and thoracic (rear) parts fused with each other. Under the shell of the cephalothorax are the gills. There is a sharp chitinous spike on the top of the head section, and two stalked, bulging black eyes are located on the sides in the recesses. The eye of a crayfish is of a mosaic type, and it is rather complicated - it consists of a large number of individual "eyes" that perceive light. In the anterior part, near the eyes, there are long chitinous stalked antennae: two pairs of long and two pairs of short ones. The antennae are densely innervated and play important role in the touch of this animal. In the lower, front part of the cephalothorax is the mouth of the crayfish. The oral apparatus is quite complex and consists of two pairs of “jaws”, which are forelimbs modified in the process of evolution. The limbs of crayfish are single-branched, and are represented by five pairs: the first pair are claws, and the remaining four pairs are walking legs. Crayfish claws are designed to capture and hold prey, protect and attack. In males, pincers play an important role as a means to capture and hold the female during the mating season. The limbs of crayfish are capable of regeneration at the end of the molt.
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Abdomen (back)

The segmented abdomen of crayfish consists of seven segments, on which there are five pairs of small biramous limbs (ventral legs) intended for swimming. The sixth pair of abdominal legs together with the seventh abdominal segment (member) forms the caudal fin.
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Digestive system

The crayfish stomach is two-chambered, and consists of two specialized sections: in the first section, the food is carefully ground (chopped) with hard chitinous “teeth”, and in the second section, it is finely filtered (filtered). Finely ground food then enters the intestines, and into the digestive gland, in which its final digestion and absorption of all nutrients. All the remnants of undigested food are then sent to the excretory system located at the back of the cancer. Removal of the remains (feces) of crayfish is carried out through the anus located in the central part of the caudal fin.
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Nervous system

The nervous system of crayfish is simple, and consists of the peripharyngeal ganglion and the ventral nerve circuit.
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Range and habitat

Reservoirs in which these invertebrates can live should have a depth of 3-5 meters and depressions with a greater depth - from 8 to 15 meters. The optimum water temperature in summer is 16-22°C.
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Behavioral Features

The crayfish actively hunts mainly at night, and during the day it hides in a wide variety of natural shelters (bog, stones, crevices, etc.). Artificial shelter for crayfish are burrows dug or occupied by them, which are usually located along the coastline in soft soil or clay. The length of the crustacean burrows reaches an average of 30-35 cm, and often reaches half a meter. In the summer, crayfish prefer shallow areas of reservoirs, and in winter period they prefer strong soil (clay, sand, etc.). Crayfish move in a peculiar way, that is, move backward, but in case of danger they swim due to sharp and strong strokes of the caudal fin, like shrimps 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 starvation. In relations between the sexes, male crayfish dominate, since they are larger than females, and in the event of conflicts between males, as a rule, the larger and stronger cancer wins.
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Nutrition

In search of food, crayfish never move far from their holes, and on average, the distance they travel from the hole ranges from 1 to 3 meters. The diet of crayfish is mainly dominated by plant food (~90%) and animal food (~10%) occupies a certain proportion. 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 molluscs, tadpoles, worms, insects and their larvae. The diet of animal food of crayfish also includes, as a constant component of food, different kind carrion - the corpses of animals and birds, which crayfish often eat "clean". In winter, crayfish also feed on fallen leaves of trees. According to researchers, it was noticed that female crayfish consume more food, but eat less often than males.
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Reproduction and development

Adult blue crayfish. Front view

Male crayfish reach puberty 3 years after birth, and females 4 years later. At the very beginning of autumn, crayfish males 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 on her back. As a rule, the male must be much larger and stronger than the female, otherwise she will simply break out of his "embrace". After quatting and turning 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 is noticed that incubation period The development of fertilized eggs in young crustaceans largely depends on the water temperature. The breeding season for crayfish is October. At the end of the development of eggs, young crustaceans with a size of about 2 mm emerge from them. After the appearance of young crustaceans, they remain on the female's abdomen for about 10-12 more days, and then, after leaving her, they switch to independent feeding, development and resettlement in the reservoir. Two weeks after birth, the size of a young crustacean reaches about 10 mm, and its 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 of the size of young crayfish occurs quite unevenly, and depends on the temperature conditions of the water and the presence of one or another amount of food. During the next year of life and development, the crustaceans go through 6 more 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 two times a year.
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Use in the food industry

Since ancient times, crayfish have been widely used as human food. The remains of crayfish shells were found in the so-called "kitchen heaps" of the Neolithic. Basically, crayfish are processed by boiling in salted water, and having acquired a peculiar red hue and appetizing smell, they are served seasoned with herbs (dill, parsley, celery, etc.). When cooking crayfish (and crustaceans in general), they turn red. The change in the color of the integument of crustaceans is explained by the fact that they contain a very large amount of carotenoids. The most common pigment found in crustaceans is astaxanthin, which in its pure form has a rich bright red color. Before heat treatment, and in live crayfish, carotenoids are associated with various proteins, and the color of the animal is usually bluish, greenish and brown tones. When heated, the compounds of carotenoids and proteins easily break down and the released astaxanthin gives the body of the animal a rich red color. The bulk of the nutritious meat of crayfish is in the abdomen, and a slightly smaller amount of it is in the claws. The meat of the crayfish is white with rare pink streaks, nutritious and has an excellent taste. In terms of composition, it contains a large amount of protein, and a low fat content. The percentage of the volume of crayfish meat in comparison with other crustaceans eaten by people becomes

it is obvious that crayfish is not a champion, although it exceeds a number of food crabs. In other words, there is little meat in adult crayfish. If a kilogram of whole shrimp has a meat content of about 400 grams, then a kilogram of crayfish is barely 100-150 grams (belly and claws), while crayfish are approximately 3-4 times more expensive. Probably the very consumption of crayfish is mainly based on the rather attractive appearance of all kinds of dishes decorated with boiled crayfish, and partly on old traditions.

Crayfish are found in almost all rivers, and larger specimens live in reservoirs with a sandy bottom. They are very tasty, and they are also used as bait for fishing.

The following types are known:

• thick-fingered;
• narrow-toed (this species has long and narrow claws);
• broad-fingered (has powerful and short claws).

The 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 in males is narrow, and in females - wide. 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 acts as organs of touch.

The organs of smell are two long whiskers. The mouth opening is located at the bottom of the head, and at the top it is surrounded by a lip and jaws, which are necessary for the digestion of food. The crayfish has eight pairs of limbs. The front three are short mandibles that help the arthropod feed. The rest - serve for movement, three pairs of them with claws, which are the most important tool. Thanks to them, cancer defends itself or, conversely, attacks the victim.

reproduction

The period of caviar gestation in crayfish is long. Two pairs of anterior abdominal legs participate in reproduction. Fertilized eggs are attached to them. Starting from autumn, the female wears it all winter and spring, and only in June-July does the offspring appear.

Moult

At this time, the chitinous cover is replaced, the gills and digestive organs are updated. Juveniles change their appearance more often than adults. The molt takes place in summer time when the reservoir warms up. In the first and second years of life of arthropods, it is carried out several times. This process lasts several minutes, usually no more than 15, in an open place. After the change of cover, the arthropod hides in a mink so that the shell hardens and gets stronger.

What do crayfish eat?

Both soft and hard plants are eaten. A favorite delicacy is the rhizome and stalk of reeds, sedges, reeds. During the day, they eat food, the mass of which is equal to 2.5% of the total weight of the arthropod. Crayfish are happy to absorb animal food:

• water worms;
• insect larvae;
• small snails;
• tadpoles;
• small fish.

Arthropod nutrition depends on age. The larvae prefer mainly animal food, which occupies about 80% of the diet. Young growth, which has reached a length of 2 mm, loves chironomids and daphnia. When they reach two years of age, daphnia leave the diet. Crayfish, body length 2 cm, begin to absorb the larvae. In the future, as the growth increases, the use of amphipods increases. They do not swallow their prey, but bite off in small pieces and slowly send it into the oral cavity.

Habitat

For comfortable living crayfish require certain conditions:

• fresh water;
• oxygen concentration should be at least 5 mg per liter of water;
• pH 6.5 and above;
• a sufficient amount of lime in habitats (otherwise, the growth of crayfish is significantly reduced);
• hard rocky bottom with low silt content.

Where do crabs live? River counterparts prefer to live on the borders of hard and soft bottom, in coastal pits or slopes of coastlines at a depth of one and a half to three meters. Best Places large and strong males are captured for permanent housing. Females and weak males live in less adapted conditions. Juveniles - in shallow water near the shore, under snags and stones. Crayfish are hermits and each of them has a shelter in which he hides from his relatives.

Arthropod hunting

Where is the best place to catch crabs? In clean rivers warm water enriched with oxygen. In some reservoirs, you can catch crayfish at a shallow depth (50 cm), while in others - from two to three meters. In rivers with a clay bottom, they dig holes, about a meter long. And also many shelters are found by arthropods in places with a rocky bottom. In the first month of summer, crayfish with a strong shell can be found on condition of a warm spring. In the case of a cool or cold summer, hunting should be postponed until autumn. Where is it useless to catch crayfish? In shallow water, in reservoirs with a sandy or muddy bottom covered with dense algae.

The best time to fish

In some regions of the country, crayfish fishing is limited or completely prohibited. They cannot be hunted during the period of bearing future offspring. In some areas, the allowable size of cancer is set, after which they can be caught.

A complete ban on these actions exists in the Moscow region and directly in Moscow itself. Therefore, you may not be interested in the question of where crayfish are found in the Moscow region. During the fishing period, no more than three traps or traps with a diameter of 80 cm and a mesh pitch of about 22 mm can be used per person. Hunting by hand by diving or wading is prohibited. For illegal fishing in each region, a fine is provided, the amount of which is different in the regions.

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 stagnant water, as well as in swamps. However, these arthropods prefer clean flowing water bodies with a gentle current.

Each of them has areas that these animals have chosen for permanent residence:

1. Coastline with stones. This is the most attractive place where crayfish are found, as they can live near the surface of the earth under the cobblestones. At the bottom of the reservoir, they build burrows and hide in them during the molting period.
2. Cliff coast. In cases where the depth in the river varies, and under the coastline it can reach two meters, crayfish settle in these places. A prerequisite is the presence of peat or silt on the bottom surface in the reservoir.
3. backwaters with snags- these are the places where crayfish are found in in large numbers. It is there that you can find quite large specimens.
4. Sandy bottom of the reservoir. It is very easy to hunt for crayfish in these places. There are few algae, the bottom is transparent and well visible. Successful hunting awaits everyone in these reservoirs.
5. shell rock. The bottom dotted with them and the presence of areas with reeds indicate the presence of crayfish in these places.
6. 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.
7. Banks in the 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.

Conditions for a quality catch

• Well ventilated and illuminated pond. In a cloudy and dark environment, crayfish will move very quickly and be difficult to catch. When hunting in such conditions, special traps are placed at noon, which are checked in the morning.
• Certain times of the day. And how to catch crayfish in the summer? In the daytime, arthropods hide and are not active. During this period, you can find those individuals that are not very well hidden, and catch them with your hands. After sunset, crayfish begin to peak activity. This time is considered ideal for setting traps. Some prefer to hunt them at night, using lanterns to search for them. When hunting in the warm season, a rich catch awaits you. In late autumn and winter, crayfish live in their burrows and do not come out until hot days.

Arthropod hunting

How to catch crayfish in the summer or in another period? First you need to find the reservoir in which they live.

• Most of the beaches have places where reeds grow, where, as a rule, people do not swim and do not scare crayfish. Slowly swim along the reeds and carefully inspect the bottom, as they hide perfectly in the reeds.
• Catching crayfish in quiet places with tree roots and snags is a real pleasure, the main thing is to know the bottom. Hunt them, it is necessary resolutely without making sudden movements. In such places, as a rule, large individuals live. They are quite slow and are not difficult for experienced catchers.
• In rivers with a rocky bottom, there are many natural burrows for crayfish, in which they often hide from danger. It is better to grab them by the whiskers than by the claws. Do not stick your hands into the holes, there is a chance of injuring them. There are cases when large stones pressed down the upper limbs of the catchers.
• In reservoirs, where the bottom is strewn with remnants of reeds, as well as river mollusks, crayfish are frequent guests. It is necessary to swim carefully, inspecting the bottom. Be careful, as you can easily injure yourself on shellfish shells.
• The most successful place for both beginners and professionals is the sandy river bottom.
• Catch crayfish in a hole must be very careful. If you find a place where the depth is two to three meters near the shore, then you can see several passages under the water. Live crayfish in such holes are very rare, these holes belong to musky rats. In crayfish, the houses are small, up to five centimeters in height and eight in width, depending on the size of the arthropod.
• Favorite place is broken bottles, in which the whole bottom remains. Most jars and flasks contain crayfish. There are a lot of such containers in almost any reservoirs.

In case you are not interested in independent hunting for cancer, then you can buy it. When choosing, pay attention to the tail. In a living crayfish, it is tightly pressed to the body.

Every time they meet with crayfish, few people know that this representative dates back to ancient times, when many crustaceans began to form. Crayfish is the same age as many dinosaurs.

This crustacean appeared and formed as separate view back in the Jurassic period, and this is about 130 million years ago. During this period of time appearance crayfish has practically not changed, and vice versa, and its population is actively growing and settling in almost all water bodies of Europe.

In general, it should be noted that the name crayfish is not entirely correct, and it would be more correct to call this representative freshwater crayfish, since it settles and lives exclusively in fresh water.

What does crayfish look like?

Like all crustaceans, crayfish has an external skeleton, which is a hard chitinous cover.

As for the color, it can vary, depending on the age of the crustacean itself and on the conditions of its habitat. But the most common combination of green, brown and brown colors.

The cephalothorax, abdomen and pincers - that's actually the whole structure of the crayfish, which breathes with the help of gill slits.

On average, crayfish live from 6 to 8 years.

Where does crayfish live?

“Where crayfish hibernate” everyone can only guess, but they naturally live in reservoirs, moreover, exclusively with fresh water. The depth of the reservoir should be at least 3 meters, it is desirable that at its bottom there are depressions up to 5 - 6 meters, and the most favorite water temperature for crayfish: 16 - 22 degrees.

Features of the behavior of crayfish

Crayfish are nocturnal. During the day, he prefers to sleep or just relax, hiding in the recesses at the bottom of the reservoir, snags, or simply in the bottom debris and silt.

Many of them build burrows for their living, which are usually located near the coastal soil, on the side of the reservoir. At the same time, the depth of the hole sometimes reaches 40 cm.

Crayfish really move in an unusual way - they move backwards. But they are able to swim in case of danger, and quite quickly, using their tail fin for this, which is capable of making powerful strokes, in fact, ensuring movement in the water.

The relationship is always dominated by the male cancer, and the more impressive his size, the more likely he is to establish control over the territory.

Also interesting is the fact that at a time when the population of crayfish in one reservoir increases dramatically, cases of cannibalism begin to gain momentum. This is probably one of the ways to keep the population at the same level, thereby preventing food shortages and starvation.

What does crayfish eat

As for the nutrition of crayfish, the basis of their diet is aquatic plants and all kinds of freshwater small inhabitants, which they get for dinner already in the form of carrion.

As for reproduction, it occurs only after the males reach the age of three, and the females even older - four years.

The active breeding season for crayfish is September - October. It was at this time that the female bears eggs fertilized by the male, from which, after two weeks, small crustaceans appear, the number of which can vary from 200 to 330 pieces, but less than half of them will survive and reach maturity. Most of the same will be the prey of freshwater fish.

Starting from the second half of the 20th century, broad-toed crayfish have been forced out of their natural habitats by another type of freshwater crayfish, introduced from the New World and disease-resistant American signal crayfish ( Pacifastacus leniusculus).

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Structure

External structure

The body length of the broad-clawed crayfish can reach 20 cm. The color varies depending on the habitat from greenish-brown to blue-brown.

Body sections

The body consists of two main sections (tagmas) - cephalothorax, or cephalothorax, and abdomen ( pleona, abdomen). On the dorsal side, the cephalothorax is covered with a massive carapace bearing a sharp outgrowth at the front end - rostrum. On the surface of the carapace there is a transverse cervical suture and two longitudinal cardiogill grooves. The lateral parts of the carapace - branchiostegites - delimit the gill cavity lying under the carapace. The anal lobe, the telson, is attached to the last segment of the abdomen.

limbs

On the sides of the rostrum are two pairs of sensory antennae - antenna I and antenna II- and a pair of compound eyes on movable stems. The oral apparatus consists of six pairs of limbs: mandible(upper jaws), two pairs maxill(lower jaws) and three pairs maxliped(jaws).

The pereon (chest), like that of other decapod crayfish, consists of eight segments and carries eight pairs of limbs - three pairs of mandibles included in the oral apparatus and five pairs of pereopods (thoracopods). First pair of pereopods ( chelipeds) is different large sizes and bears pincers, larger in males. The remaining four function as walking legs; the first two pairs carry small pincers used to clean the body and capture food. Epipodites transformed into branched gills extend from the outer side of the mandibles and pectoral legs into the cavity under the carapace.

The pleon consists of six distinct segments and an anal lobe, the telson. In females, this part of the body is wider than in males. The extremities of the first segment in males are transformed into a copulatory organ, while in females they are partially reduced. The next four bear swimming limbs - pleopods (in males, the limbs of the second segment are also modified). On the last segment are uropods and a telson, forming a caudal fin similar to an open fan.

Internal structure

The stomach consists of two sections: cardiac and pyloric. In the first, food is ground with calcified chitinous teeth, and in the second, it is differentiated with the help of a complex filtering apparatus. At the same time, too large food particles are excluded from digestion, and those that have passed through the filter enter the digestive gland, a complex system of outgrowths of the midgut, where digestion and absorption actually take place. Undigested residues are brought out through the anus located on the telson.

The circulatory system in crayfish is not closed. Oxygen dissolved in water penetrates through the gills into the blood, and carbon dioxide accumulated in the blood is excreted through the gills. The nervous system consists of the peripharyngeal nerve ring and the ventral nerve cord.

Habitat

Fresh clean water: rivers, lakes, ponds, fast or flowing streams (3-5 m deep and with depressions up to 7-45 m). In summer, the water should warm up to 16-22 °C. Crayfish are very sensitive to water pollution, so the places where they are found speak of the ecological purity of these reservoirs. It also lives in Chagan, the Urals.

Nutrition

Vegetable (up to 90%) and meat food (mollusks, worms, insects and their larvae, tadpoles, carrion). In summer, crayfish feeds on algae and fresh aquatic plants (weed, elodea, nettle, water lily, horsetail), in winter - fallen leaves. At one meal, the female eats more than the male, but she also eats less often. The crayfish looks for food without moving far from the hole, but if there is not enough food, it can migrate 100-250 m. vegetable food and also dead and living animals. Active at dusk and at night (during the day, crayfish hide under stones or in burrows dug at the bottom or near the coast under tree roots). The smell of food can be felt at a great distance, especially if the corpses of frogs, fish and other animals have begun to decompose.

Like other scavengers, crayfish can often be carriers of diseases dangerous to humans, such as: typhoid and group A hepatitis [ ] .

Behavior

Crayfish hunt at night. During the day, it hides in shelters (under stones, tree roots, in burrows or any objects lying on the bottom), which protects it from other crayfish. It digs holes, the length of which can reach 35-120 cm. In summer it lives in shallow water, in winter it moves to a depth where the soil is strong, clay or sandy. There are cases of cannibalism. Contrary to popular belief, cancer moves in its natural environment in a quite usual way - head forward, and not back at all. He can back up on land, for example, a crayfish caught and laid on the ground will back up, trying to hide. But the crayfish really swim backwards, raking in the tail plate. In case of danger, with the help of a caudal fin, it stirs up silt or swims away with a sharp movement. In conflict situations between a male and a female, the male always dominates. If two males met, then the larger one usually wins.

Reproduction and development

At the beginning of autumn, the male becomes more aggressive and mobile, attacks the approaching individual even from the hole. Seeing the female, he starts the pursuit, and if he catches up, he grabs her by the claws and turns her over. The male must be larger than the female, otherwise she may break out. The male transfers the spermatophores to the female's abdomen and leaves her. In one season, he can fertilize up to three females. After about two weeks, the female spawns 20-200 eggs, which she carries on her abdomen.

Puberty: males - 3 years, females - 4.

Pregnancy/incubation: dependent on water temperature.

Lifespan: 20-25 years.

Offspring: newborn crustaceans reach a length of up to 2 mm. The first 10-12 days they remain under the belly of the female, and then move on to independent existence. At this age, their length is about 10 mm, weight 20-25 mg. In the first summer, the crustaceans molt five times, their length doubles, and their weight six times. The next year they will grow to 3.5 cm and weigh about 1.7 g, shedding six times during this time. The growth of young crayfish occurs unevenly. In the fourth year of life, crayfish grow to about 9 cm, from that moment they molt twice a year. The number and timing of molts are highly dependent on temperature and nutrition.

To belong to the order of arthropods, the animal is quite ancient, which appeared about 130,000,000 years ago, back in the Jurassic period. Over the past period, the appearance of this crustacean has practically not changed. This arthropod is also called the European freshwater or noble crayfish. The population of this animal continues to grow, it actively breeds in almost any European reservoirs. The name "crayfish" is not entirely true: these arthropods, in addition to rivers, live in lakes and ponds, for this reason it is much more rational to call them freshwater.

Appearance and characteristic features of the structure of crayfish

Crayfish have a body reaching a length of 15-30 cm, covered with a hard, chitinous shell, forming a strong skeleton that can withstand predator attacks. The shell of this animal can be colored brownish, greenish-brown, or black, with a bluish tint. The color depends on the composition of the water and other living conditions. Such shell colors allow crayfish to successfully hide at the bottom of the reservoir.

The body of this animal is formed by a powerful cephalothorax and an abdomen consisting of 6 segments. A sharp chitinous spike can be seen at the top of the head, and on both sides of the side there is a pair of eyes sticking out on moving stalks. The functions of touch and smell are performed by the antennae located near the eyes. This inhabitant of freshwater reservoirs breathes with the help of gill slits.

Located on the sides of the mouth, the upper and lower jaws, in fact, are modified limbs. Each of the parts of the thoracic region is equipped with two single-branched limbs. In total, this animal has 5 pairs of limbs, one of which is a claw used for food and protection from enemies. The rest of the limbs are used for movement.

A powerful shell reliably protects against enemies of cancer. But at the same time, he does not allow him to fully develop, for this reason, the cancer periodically sheds a hard chitinous cover during the molting period. The approach of this period can be determined by the shell, which acquires a matte hue. At the same time, molting occurs more often in young individuals than in adults.

Male and female individuals of this animal in a certain way differ in the structure of the body. Females are noticeably smaller than males, which also differ from them in more impressive claws and rather narrow abdominal segments. Females have a wider “tail”, under which, during spawning, eggs are located and hatch until the crustaceans are fully formed. Life cycle of these arthropods is approximately 6-8 years old, but in some cases they live up to 10.

crayfish habitat

Contrary to popular belief, crayfish are not so unpretentious in choosing a reservoir. Most of all, they like to settle in reservoirs with a hard and not very muddy bottom, preferring to be located at a depth of 1.5 to 3 m, at the bottom and in holes near the shore. Young individuals can be found in shallow water, at a slight distance from the coastline. In a dense clay bottom and on cliffs, they are able to dig holes up to 1 meter deep, which is carefully guarded.

These animals cannot tolerate high levels of acidity, the ideal pH for their habitat should be between 6.5 and above. These crayfish cannot live in the salt water of the sea. If a lime deficiency is found in a reservoir, the crayfish living in this place will grow much more slowly. The most suitable water temperature for these inhabitants of freshwater reservoirs is 16-22˚С. They prefer to lead a nocturnal lifestyle, hiding under snags during the day, hiding at the bottom, in various depressions, or digging into the silt.

Types of crayfish

In total, it is customary to distinguish 3 types of arthropod data:

• Thick-toed (Astacus pachypus). It can live in both fresh and brackish water. This species is endangered. Its numbers are gradually moving towards a critical level, which can eventually lead to extinction.

• Broad-toed (Astacus leptodactylus). In the last century, it almost died out due to an epidemic of crayfish plague. characteristic feature is an impressive life expectancy (about 25 years). Lives exclusively in clean waters.

• Narrow-toed (astacus astacus). It has a more elongated body and much more elongated claws. Unlike the broad-toed, it can easily live in not very clean water.

Features of cancer nutrition

Crayfish is a twilight inhabitant of water bodies. It feeds most actively at dawn and after sunset. In cloudy weather, he can engage in obtaining food not only at night. Crayfish are not in the habit of moving a long distance from their home, even in search of food. The distance traveled by these animals from the holes is, in most cases, 1-3 meters. Crayfish prefer predominantly plant foods, which make up 90% of their diet, but sometimes animals are not neglected. Plant foods include: various algae and certain types of plants (in particular, horsetail, pondweed, elodea, as well as water lilies and nettles). In winter, crayfish can also feed on fallen leaves. Animal food includes: insects and their larvae, worms, tadpoles and various mollusks. Do not disdain crayfish and carrion, which is a constant component of their diet. Often crayfish completely eat the corpses of animals and birds.

There are several methods for catching crayfish. Most people prefer to catch these bottom dwellers with their hands. Some use special devices for this: crawfish, crayfish of various designs.