These small relatives of lobsters are representatives of the ancient world, since they appeared back in the Jurassic period. From the name it becomes clear that they inhabit rivers and rivulets. They are also found in lakes, streams, ponds, estuaries and even swamps.
Appearance
Crayfish is the highest cancer, a decapod squad that brings together highly organized crayfish, as well as crab and shrimp. In all representatives of this detachment, 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 cancer, you can easily notice that its body consists of two parts: the cephalothorax (which is the fused head and chest segments, the fusion seam is clearly visible from the back) and the jointed abdomen ending with a wide tail. The cephalothorax is hidden under a solid 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 cancer are safely hidden under it, and the muscles of the arthropod are attached to it. On his head are two pairs of antennas or antennae, covered with bristles and having a very long length, so the name “antenna” is more suitable for this organ. They perform the function of smell and touch, so the crayfish are nowhere without them. In addition, at their base are the organs of balance. The second pair of antennae is inferior in length to the first, and is needed only for touch.
On the front of the cephalothorax there is a sharp spike; black convex eyes are located on its sides in the recesses. They are located on long movable stems, so that their cancer can rotate in all directions. This helps the animal to view the space around it well. The eye has a complex facet structure, that is, it consists of a large number of small-sized eyes (up to 3 thousand).
Claws are attached to the chest - these are the forelimbs. With them, he defends himself from enemies, catches and holds the victim, and he also lets them in during the fertilization period of the female, in order to detain her and turn her on her back. From this it becomes clear that romance in inter-sexual relations is alien to the crayfish.
For movement, the animal uses four pairs of long, walking legs. In addition, he has small legs that are located on the inner surface of the abdomen and are called abdominal. They perform a significant function, helping the cancers breathe. They arthropod representatives drive oxygenated water to the gills. They are covered with a thin shell and are located under the cephalothorax shield, the latter creating a cavity for them.
Crayfish have to constantly work with their legs and pump fresh water through the cavity. Cancer females still have a pair of miniature bifurcated legs on which she holds eggs with developing crustaceans.
The last pair of limbs is lamellar tailed legs. In a tandem with a thickened telson (this is the last segment of the abdomen), they play an important role in swimming, thanks to them, cancer has the ability to quickly make “legs” backwards. Frightened, the cancer instantly leaves the place of danger, making sharp vertical movements of the tail, raking it under itself.
An arthropod also has a no less complex structure. He has 3 pairs of jaws. Each of which has a specific task - one grinds food, the other two work as sorting stations. They sort food particles and transfer them into the mouth.
Sexual dimorphism, that is, the anatomical difference between the female and male individuals of the same species, is present in these arthropods, although it is not pronounced.
Female and male - who is in front of us?
The female cancer is significantly inferior in size to the male, it is more miniature and elegant in contrast to the male. The same can be said about the size of its claws - they are more modest in size. Her belly is noticeably wider than the first part of the body - the cephalothorax, whereas in the male it is already his. And also a distinctive feature is the condition of two pairs of abdominal legs. In the female half of the cancers, they are underdeveloped, in males they are well developed.
Their color depends on the habitat, the composition of the water. By color, the crayfish merge with the bottom of the reservoir, and "dissolve" among the stones and snags. Therefore, they are usually brown, brown with a greenish or bluish tint.
In length, they grow to 6-30 cm. But how much they live, there is still no exact answer to this question. Experts cannot decide on their life expectancy. Some believe that cancers live up to 10 years, while others give them a much longer life span, speaking of a 20-year life expectancy.
Area
Some crayfish prefer fresh water, others need brackish water. Many representatives of these crustaceans live in crystal clear water. Therefore, if crayfish were 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 counterparts to pollution, sometimes populates waters of poor quality, which misleads the person.
Cancers need a sufficient concentration of oxygen in water and lime. With oxygen starvation, they die, and with a lack of lime - their growth slows down. The bottom they prefer non-clay or with a small content.
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.
Kinds
There are 4 types of crayfish:
- Endangered Species - Fat Cancer, its number is so small that today it is on the verge of extinction. They live in the adjacent territories of the Black, Caspian and Azov Sea in clean, brackish water. Do not withstand a sharp increase in water temperature. It should not rise above 22-26 ° C. In length, it grows up to 10 cm. His body is painted in brownish-green color. Claws are dull, slightly forked.
A characteristic feature of thick-clawed cancer is a sharp notch on the fixed part of the claw, which is limited by tubercles in the shape of a cone. Does not live in contaminated areas.
- Wide-toed view found in many clean, fresh waters in the European part of the country. They can be found in any running body of water where the water warms up to 22 ° C during the summer months. In length, this olive-brown or brown with a bluish tint representative grows up to 20 cm. Its claws are short and wide. In reservoirs with dirty water can not be found. Recently, its population is declining, is under protection.
- Narrow-toed cancer feels good in fresh and brackish water, lives in the areas of the Black and Caspian Sea, slow-flowing rivers, low-lying reservoirs. The length of his body reaches 16-18 cm, thirty-centimeter specimens are also caught. Chitin shell is painted brown - from light to dark. Its claws are very elongated - narrow and long. It is more resistant to pollution, therefore, it can populate contaminated water bodies.
- American signal cancer spread in many reservoirs of Europe, displacing other species. It was introduced to European countries after a decrease in the population of local types of crayfish due to the "Crustacean plague." If we talk about Russia, then its appearance was registered only in the Kaliningrad region.
Fat crayfish
Wide-toed cancer
Narrow-toed cancer
American signal cancer
In appearance, the "American" looks like a wide-toed representative of crustaceans. A distinctive feature is a white or blue-green spot, which is located on the claw joint. In length, it reaches 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 the plague of cancers - a mycotic disease from which river cancers massively die, but is a carrier of infection.
Nutrition
Freshwater crayfish are omnivorous, their diet is diverse - it has both plants and animals. For most of the season, their menu is dominated by plant foods. From plants, it tastes like algae and stalks of water lilies, horsetail, pond, elodea, water buckwheat. In winter, they eat up fallen leaves.
But for normal development, they need food of animal origin. They like to eat snails, worms, plankton, larvae and water fleas. They do not disdain carrion, eating at the bottom of a reservoir of dead birds and animals, prey on sick fish, that is, in a way, they are orderlies of the aquatic ecosystem.
Crayfish do not kill their victim, do not inject them with poison to paralyze it. They, like real hunters, hatch in an ambush, and instantly capture a gaping victim with claws. Holding it tightly, they gradually bite off a small piece of it, so dinner at the crayfish stretches for a long time. Experts, with a lack of food in the pond or overpopulation, observed cases of cannibalism in them.
After wintering, mating and molting, crayfish prefer food of animal origin, the rest of the time they feed on vegetation. Feeding aquarium and pond crayfish is described in this article.
Lifestyle
Crayfish usually show activity in the dark or at dawn, but in cloudy weather they also get out of their minks. These are hermits. Each arthropod lives in its own mink, which is dug by the size of its inhabitant. This helps to avoid the invasion of uninvited guests and the penetration into the home of their relative or enemy.
In the afternoon, they spend all their time in their shelters, closing the inlet with claws. At the time of danger, the crayfish back away and go deeper into the hole, the length of some is up to 1.5 meters. Going in search of food, they are not far from their home, moving slowly along the bottom, putting forward claws. If the prey is in range, then they act with lightning speed. He has the same quick reaction in moments of danger.
In summer, cancer usually lives in shallow areas, and with the onset of cold weather goes to depth. Females hibernate separately from males, because at this time they hatched eggs and hide in minks. The male crayfish half "heaps", gathering together several dozen individuals, overwinter in pits or burrow in the silt.
Breeding
Males are ready for breeding when they reach 3 years, puberty of the female is longer by 1 year. By this time, crayfish grow to 8 cm in length. Among sexually mature individuals, there are always 2-3 times more females than males.
Mating takes place in the cold season and falls on October - November. Timing may shift due to weather or climatic conditions. The male can fertilize only 3-4 females. If in most fauna representatives this process usually occurs by mutual agreement, then in the case of arthropods, mating resembles an act of violence.
Already in September, males noticeably become very mobile and show aggression towards individuals swimming past them. The male, seeing a female nearby, begins to pursue her and tries to grab her with claws. That is why crayfish are much larger than females, since she will easily throw off a feeble cavalier herself.
If the male managed to catch up with the female, then turning her on her back, he transfers his spermatophores to her abdomen. Such violent insemination sometimes ends with the death of the female, and fertilized eggs also die with it. On the other hand, the male spends a lot of energy chasing and practically does not eat during this period, often he catches the last female, he simply eats to strengthen his strength.
A fertilized female lays eggs after 2 weeks, which attaches to the abdominal legs. She has had a hard time all this time - she protects future offspring from enemies, provides eggs with oxygen, cleans them of silt, algae and mold. In this case, most of the masonry perishes, the female usually saves about 60 eggs. After 7 months in June-July, crustaceans peck out from the caviar, measuring only 2 mm in size and remain on the mother’s abdomen for 10-12 days. Then the crustaceans start free swimming, settling in the pond. At this point, they reach a length of 10 mm and weigh about 24 g.
Molting
As mentioned above, a durable chitinous shell reliably protects cancer from the sharp teeth of the enemy, but on the other hand, it inhibits its growth. However, nature has taken care of solving this problem, and it has the ability to periodically completely reset the old carapace. Not only the chitinous coating of cancer is updated, but also the upper layer of the retina of the eyes and gills, part of the digestive tract.
In young crustaceans, in the first summer, the carapace changes up to 7 times, with age, the number of molts decreases and the adult individual costs one molt per season. The change of the shell occurs only in the summer, when the water in the lake or river warms up.
Do not think that this process of “rebirth” proceeds easily and quickly. It can last from several minutes to a day. Arthropod with great difficulty first releases the claws, then the rest of the legs. When molting, the limbs or antennae often break off, and the cancer lives without them for some time. Over time, the lost parts grow back, but have a different look. Therefore, often rakolovy catch animals with different claws in size, one of them may have an ugly or underdeveloped shape.
Under the old “skin”, a new soft cover is already formed for the molt until it hardens, and for this it takes 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 neither in the shelter, but in the open space, he needs to safely get to his place of residence, where he can sit up to 2 weeks without food, and wait until the cover is more or less keratinized.
Crayfish fishing and hunting
Crayfish are caught all year round, they refuse to hunt them during molting, because the taste of meat is deteriorating. But this rule is valid in those regions where it is quite common.
In some areas where the population of arthropods is on the verge of extinction, fishing is completely prohibited, for example, in the suburbs or only allowed for a certain period, as in the Kursk region. It is usually forbidden to catch crayfish during the period of fertilization and gestation by females.
Going for a catch, you need to find out what size and how many cancers can be caught. If you catch smaller arthropods, you may face an administrative fine. The market size of the crayfish, each region sets its own, but usually it is 9-10 cm.
How to catch?
There are 5 main ways to catch crayfish:
- Hand fishing. This is the most primitive way. The crayfish hunter must observe silence, carefully moving along the river, and look under every stone, driftwood, fallen trunks. As soon as the cancer is detected, immediately grab it and pull it out.
- On the shoe. The method was invented for a long time, but it is less effective. The old shoe, it is better to take it in large size, is filled with bait and thrown to the bottom. It is checked from time to time.
- With scuba gear. Some cancers practice scuba diving. This method is quite rare, if not exotic.
- On a cancer rod. The cancer rod has a simple device.They attach a fishing line to a stick with a pointed end, which is stuck into the ground, and a bait to its end. Fresh fish or a frog are used as bait. The bait is folded into a nylon stocking and a pinch of bloodworm is added. And to make the smell stronger, the fish should be “flattened out”. Clinging to the "victim" of cancer, this can be seen by moving the sticks, fishing line or feeling the tremors of the rod, carefully pulled out. However, at any time, the catch may break.
- Using rakolovki. Shells 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 pond. Every 20 minutes they are picked up and checked, having pulled out the catch, the rakolovka is sent back to the bottom. It is more practical to use closed structures, since it is difficult for crayfish to climb out of them.
The last two ways are considered more athletic.
When to catch?
Crayfish are best caught in the fall, when the water gets cool and the day is shortened, therefore, the time for hunting increases, 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, cattail or reeds grow.
How and when to catch crayfish is described in this article.
The chemical composition of cancer
They catch cancer for the sake of tasty, healthy and tender meat. The lion's share in it falls on proteins - 82%, fats - 12%, and carbohydrates - 6%. In 100 g of edible part, only 76 kcal.
There are many different vitamins in meat: almost all representatives of group B, fat-soluble ones - A and E, nicotinic and ascorbic acid. The mineral composition is also diverse - potassium, phosphorus, sodium, sulfur, calcium, magnesium, iodine and iron.
The benefit of cancer meat is due to the fact that the vitamins and minerals in it are balanced. Low calorie content and a lot of easily digestible protein makes it indispensable for dietary nutrition. And also experts advise it to be used by people with cardiovascular diseases and the liver, with disorders of the nervous system and blood circulation. However, cancers are strong allergens, in case of intolerance to the product they immediately refuse it.
Cooking Application
The tender and nutritious meat of the crayfish could not leave the cook unattended. And although only 150 g of meat is obtained from 1 kg of crayfish, the number of delicious recipes with it is huge. They are added to salads and soups, stewed, boiled, baked with Parmesan cheese, simply fried in oil. The meat goes in side dishes with seafood, from which they cook aspic.
The value of crayfish for the environment
It should be noted the benefits of crayfish for the ecosystem. They do not allow carrion and organics to decompose at the bottom, thereby inhibiting the development of pathogenic microorganisms. On the other hand, some experts believe that eating fish caviar, they have a negative impact on the population of the latter, although this is not proven by facts and is more relevant to the assumptions.
Breeding
Breeding crayfish is widely practiced worldwide. Each country has its own technology for growing arthropods, but they all follow the rules:
- bottom of reservoirs with a small amount of silt;
- the presence of pure fresh water, rich in oxygen;
- compliance with the temperature regime;
- compliance with the composition of water.
One of the most economical breeding methods is considered pond. It consists in arranging several ponds (usually in the amount of 3-4 pieces), in which crustaceans are grown.
With a great desire, crayfish can be grown at home - in the aquarium. The main thing is to find females with caviar, which is attached to their abdomen. They are released into the water and eggs are incubated, it is necessary to monitor the water circulation and aeration of the water.
It is worth taking care of the feed base in advance. Crustaceans are fed when the water heats above 7 ° C heat, boiled or fresh food, placing it on special trays.
Small crustaceans, which were shed for the 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. The crayfish, which turned one year old, are released into the feeding pond, here it is necessary to reduce the density of planting. They reach marketable size in the 2nd or 3rd year.
Crayfish conservation
In the natural environment, due to environmental degradation, general pollution of water bodies and unlimited fishing, their numbers are declining annually. From crayfish on the verge of extinction there is a thick-toed species, and the population of wide-toed species also "aspires" to this. They are listed in the Red Book, and fishing on them is strictly prohibited.
Interesting Facts
There are several interesting facts about crayfish that you should know:
- river cancer has 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 to be “non-kosher” food;
- during cooking, all the pigments that are responsible for the color of the cancer decay, except for carotenoids, which is why after heat treatment it turns red;
- previously it was believed that these arthropods are insensitive to pain, experts have proved that this is not true, when people make crayfish alive they doom them to a painful death;
- the largest crayfish are caught on the island of Tasmania, its length is 60 cm.
In conclusion, it is worth noting that the meat of crayfish is rich in trace elements that have a beneficial effect on the human body as a whole. However, it is not only healthy, but also delicious. That is why crayfish is one of the most popular representatives of arthropods.