Many people know the broad-toed crayfish not only in appearance, but also in taste. But few people know that this mustachioed is very ancient, he has survived to our times since the Jurassic period, so he even saw dinosaurs with his mobile eyes. It should be noted that since ancient times, cancer has not changed outwardly, retaining its prehistoric individuality. Let's analyze the various stages of his life, describe the characteristic external features, talk about the habits and disposition of this amazing inhabitant of fresh waters.
View origin and description
The broad-toed crayfish is a representative of the order of decapod crayfish from the crustacean family under the Latin name Astacidea. Decapods can be called the most extensive order of the class of higher crayfish, which contains 15 thousand modern varieties and 3 thousand fossils. As already noted, crayfish inhabited our planet 130 million years ago (in the Jurassic period), which makes it even more amazing and interesting to study. It would be more correct to call it freshwater, because. It is in this water that he lives. It was nicknamed broad-toed because of its wide massive claws, thereby denoting its difference from its narrow-toed river counterpart.
Video: Broad-toed crayfish
In addition to differences in the width of the claw, the broad-toed crayfish has a notch with sharp tubercles on the inside of the immovable finger, which is absent in the narrow-toed relative. The female is smaller than the male crayfish. Her claws are also noticeably smaller, but she has a wider abdomen. In addition, two pairs of ventral legs in the female are in an underdeveloped state, unlike the same legs in males.
In general, the broad-toed crayfish have a rather large, massive, jointed body, which covers the strong shell of their chitin. It is easy to guess from the name of the detachment that the crayfish has five pairs of walking legs. The first two pairs are represented by claws. If we talk about the dimensions of this crustacean, then it can be called the largest of the freshwater crayfish that live in our country. The average size of females is about 12 cm, and males are from 15 to 16 cm. Extremely rare, but there are males up to 25 cm long and weighing about two hundred grams. Crayfish of a very advanced age, which are about twenty years old, reach such sizes and weights, therefore such specimens are rarely found.
Appearance and features
If everything is clear with the size of the cancer, then its color is different, it all depends on the places of permanent crustacean deployment.
It can be:
- dark olive;
Crayfish have an excellent camouflage talent, so they competently merge with the color of the bottom of the reservoir where they have a permanent residence permit. Looking at the crayfish, it is immediately noticeable that its body consists of two main parts: the cephalothorax, consisting of segments of the head and sternum (the place where they are fused can be observed on the dorsal part) and the jointed abdomen, which ends with a wide tail part. The cephalothorax, like armor, protects a strong chitinous shell.
The shell plays the role of a crustacean skeleton, under which all the internal organs are hidden, it also serves as a mount for the muscles of the crustacean. Immediately striking are the long antennae, which are very sensitive and perform olfactory and tactile functions. At their base are the organs of crustacean balance. The second pair of whiskers is much shorter than the first, it is used only to touch. The crayfish head begins with a sharp protrusion called the rostrum. On both sides of it there are bulging eyes-beads of black color in the recess. It seems that the eyes of cancer grow on thin stems that have mobility, so the mustachioed person has a decent view, nothing can be hidden from him. .e. consist of several thousand small eyes (about 3000 pieces).
The mouth of a cancer is a rather complex apparatus, which consists of various limbs:
- one pair of mandibles, which are the upper jaws;
- two pairs of maxillae, acting as the lower jaws;
- three pairs of maxillipeds, otherwise they are called leg jaws.
The most anterior legs of cancer are called claws, they act as a grasping, holding and defensive apparatus. To move, the crayfish needs its long walking legs in the amount of four pairs. The arthropod also has smaller-sized limbs, called abdominal ones. They are essential for the respiratory system. Their crayfish are used to drive oxygenated water to the gills. Females are endowed with another pair of biramous limbs necessary for holding eggs
The crayfish tail is immediately noticeable, because it is quite long and large. Its last flatter segment is called the telson, it is very helpful in swimming, which is done backwards. No wonder they say that crayfish, namely, back away. Raking its tail under itself with vertical movements, the crayfish retreats with lightning speed from the place where it felt threatened.
Where does the broad-clawed crayfish live?
The broad-toed crayfish has chosen Europe, the only exceptions are Greece, Spain, Portugal and Italy, it is not found on the territory of these states. People artificially settled it in the reservoirs of Sweden, where it perfectly settled down and settled down, perfectly adapting to new places of existence. These arthropods settled in water bodies located in the Baltic Sea basin. Cancer lives in such countries of the former Soviet Union as Lithuania, Estonia and Latvia. This crayfish species is found in the territories of Belarus and Ukraine. As for our country, here cancer is found mainly in the northwest.
The broad-toed crayfish loves flowing fresh water. The mustache feels at ease and at ease where the water warms up to 22 degrees in summer. Cancer avoids polluted water bodies, so its settlement in one place or another indicates the purity of the water, which distinguishes this species from its narrow-toed relative, which can also live in dirty waters. The broad-clawed crayfish lives not only in flowing reservoirs, it can be found both in a pond and in a lake, the main thing is that the environmental conditions there are favorable. For permanent residence, the crayfish chooses depths from one and a half to five meters.
Interesting fact: Crayfish need water bodies that are sufficiently concentrated with oxygen, the lime content should also be normal. With a lack of the first factor, cancers cannot survive, and a small amount of the second leads to a slowdown in their growth.
Crayfish are very sensitive to any kind of water pollution, especially chemical ones. They do not like the bottom, richly covered with silt. For permanent deployment, underwater places are chosen, where there are a lot of all kinds of snags, depressions, stones and tree roots. In such secluded corners, the mustachioed equip themselves with reliable shelters. Where the water temperature does not reach even 16 degrees, crayfish do not live, because in such cool conditions they lose their ability to reproduce.
Now you know where the broad-toed crayfish lives. Let's see what he eats.
What does the broad-toed crayfish eat?
Broad-toed crayfish can be called omnivorous, their menu consists of both plant and animal food. Of course, vegetation predominates in the diet, if calculated, then in percentage terms, its indicator is 90.+-
Cancer bites with great pleasure on various aquatic plants:
- water buckwheat;
- water lily stalks;
- charophytes containing a lot of calcium.
In winter, cancer eats fallen leaves that have flown from coastal trees and fallen into the water. To develop fully and in a timely manner, crayfish need animal food that contains a lot of protein. Whiskers are happy to eat all kinds of worms, larvae, snails, plankton, water fleas, tadpoles, amphipods. It should be noted that mollusks are used along with their strong shells. Do not bypass crayfish and carrion, which they smell from afar, its smell attracts them. Crustaceans eat the corpses of animals and birds that have fallen to the bottom, eat dead fish, hunt for sick or injured fish, acting as underwater cleaners or orderlies.
Crayfish feed at night and twilight, and during the day they hide in their secluded burrows. Their sense of smell is well developed, so they smell their potential prey from afar. Crayfish do not like to go far from their holes, therefore they find food nearby. Sometimes, if there is nothing to eat nearby, they have to move, but no further than 100 – 250 meters. The hunting of crayfish is quite peculiar, they prefer to catch prey directly from the shelter, grabbing it with powerful claws. They are not able to kill with lightning speed, dooming those caught to long death torments. Crayfish, like a vise, hold soybean prey in strong claws, biting off a small piece of flesh, so their meal is quite long.
Interesting fact: With a lack of food or an increase in crayfish numbers in the reservoir, crayfish are able to eat their own kind, i.e. they have such an unpleasant phenomenon as cannibalism.
It has been noticed that when the crayfish wintering ends, the molt ends and the mating process comes to an end, they prefer to snack on animal food, and the rest of the time they eat all kinds of vegetation. Crayfish kept in aquariums are treated with meat, bread products, and various vegetables are included in the diet. Breeders have found that mustachios are partial to turnips and carrots. It is worth noting that females eat more food, but snack much less often.
Character and Lifestyle Features
The broad-toed crayfish can be called a twilight inhabitant of the water depths, because it is active at night and during predawn twilight, sometimes in cloudy weather. Each mustachioed is the owner of its own hole, where it stays during the day, putting out mobile eyes and long antennae, and placing powerful claws at the entrance. Crayfish love peace and solitude, so they carefully guard their lair from intruders.
Interesting fact: The length of cancer burrows can reach up to half a meter.
When cancer feels threatened, it retreats deeper into its dark sanctuary. Crayfish search for food not far from the hole, while they move slowly, putting their large claws forward. The movement is carried out in the usual way, but during a threatening situation, the crayfish really move backwards, paddling with their powerful tail, like an oar, swimming away in swift jerks. It should be noted that the reaction when meeting prey and at the moment of threat in crayfish is simply lightning fast.
In the summer, the crayfish moves to shallow water, and with the onset of autumn it goes deeper, where it hibernates. Females hibernate separately from males, during this period they are busy carrying eggs. For wintering, crustacean cavaliers gather in dozens and plunge into deep-sea pits or bury themselves in a layer of silt. Conflicts often occur between cancers, because each of them jealously guards his refuge from any encroachment from the outside. If a controversial situation has matured between representatives of different sexes, then the male always acts as a dominant, this is not surprising, because he is much larger. When the interests of two mature males clash, a fight breaks out, the winner of which, usually, is the one who has larger dimensions.
It is worth paying special attention to the process of crustacean molting, which occurs throughout his life. In young animals in the first summer period, this happens up to seven times. The older the cancer, the less shedding becomes. Mature specimens are subject to this procedure once a year during the summer season. By the time the molt begins, a new cover of soft tissues forms under the shell. Molting for many crustaceans is a painful, difficult process of releasing from the old shell. Often, at the same time, claws and antennae can break off, then new ones grow, which differ in size from the previous ones. Crayfish wait about two weeks in their shelters until the skin hardens, during which time they are on a strict diet. So, being in the skin of a crustacean is not at all easy.
Social structure and reproduction
Male crayfish become sexually mature at the age of three, and females closer to four years of age. During this period, their length varies within eight centimeters. Among mature crayfish, there are always two to three times more cavaliers than partners. The mating season for crayfish takes place in autumn in October or November, it all depends on the climate of a particular area. Each male fertilizes about three to four females. Already with the advent of September, the activity and aggression of males increases.
The process of intercourse in crayfish is very peculiar, it doesn’t even smell of mutual consent, the male forcibly forces the female to copulate, behaving very harshly towards her. He pursues his partner, grabs her with strong claws, lays her on the shoulder blades and transfers his spermatophores to the female's abdomen. No wonder male cancer is much larger, otherwise he would not have coped with the obstinate partner. Sometimes such barbaric intercourse can lead to the death of both the female and the fertilized caviar.
An interesting fact: a male, exhausted by mating races and battles, who practically does not eat during this turbulent time, can dine with the last partner he caught so as not to weaken at all.
This is such an unenviable lot for female crayfish, which is why they try to hide from the male as soon as possible immediately after fertilization. Egg laying occurs after two weeks, they are attached to the abdominal legs of the female. She has to protect future children from all sorts of dangers, provide oxygen to the eggs, clean them from various contaminants, and make sure that they are not affected by mold. Most of the eggs die, leaving only about 60 pieces. Only after a seven-month period, microscopic crustaceans appear from them, about two millimeters long.
Babies continue to exist on the mother's abdomen for about twelve more days. Then the kids go to an independent life, looking for their shelter in the pond, during this period their weight does not exceed 25 g, and the length does not go beyond one centimeter. They are waiting for a whole series of links and transformations over the years. Only elderly crayfish are not subject to molting. And their life expectancy is considerable and can reach up to 25 years, but crayfish rarely live to such a deep old age, their average life is about ten years. cancer
Despite the fact that cancer, like a knight in armor, is covered with a strong shell, it has many enemies in its natural environment. The most malicious of them is the eel, it poses a threat to mature large individuals, penetrating into the very depths of their secluded dwelling. Crayfish are eaten by burbots, pikes, perches. The mustachioed is especially vulnerable during the molting process, when the old shield has already been thrown off, and the new one has not gained sufficient hardness. The situation is aggravated by the fact that crayfish are in open water during the molting process, therefore they often become victims of various predators, not swimming in soft skin to their lair.
Young crustaceans are eaten in large quantities by voracious perches. Crayfish larvae and newborn babies can be eaten by bream, roach and other fish species that collect food from the bottom of the reservoir. Among mammals, minks, otters and muskrats are the enemies of crustaceans. In those coastal zones where these predators eat, you can find crustacean shells left over from dinner. Do not forget that cannibalism is characteristic of crayfish, so they themselves can easily gobble up their relatives.
Crayfish plague also acts as the most dangerous enemy of these arthropods, we will dwell on it in more detail a little later. Of course, people are enemies of broad-toed crayfish, because their meat is considered a delicacy, so new ways are being invented to catch these aquatic inhabitants, and poaching often flourishes. By polluting water bodies, a person also does a disservice to crayfish, because this species does not take root in waters with poor ecology.
Population and species status
To follow 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 that settled in many fresh European waters. But everything changed, starting in 1890, when one influential German, Max von dem Borne, brought about a hundred American signal crayfish to the United States, which he settled in the reservoir of his village.
These emigrants crossed the river to other water bodies, where they firmly established themselves. American crayfish were carriers of crayfish plague, they themselves had immunity to this disease, which, unfortunately, was absent in broad-toed crayfish. The infection struck a huge number of river arthropods, they disappeared completely from many places. This situation has led to a large reduction in the number of broad-toed crayfish.
So, from a numerous species, the broad-toed crayfish 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-clawed crayfish. Now the situation with the size of the crayfish population is also not very favorable, it continues to decline as before. This is due not only to diseases, but also to the massive catch, the poor ecological situation in many reservoirs, so the broad-toed crayfish needs special protection measures.
As already mentioned, the broad-toed crayfish is considered a small vulnerable species, whose population continues to decline, which causes concern among environmental organizations that are taking all possible measures to save it. :
- an epidemic of crayfish plague;
- the displacement of broad-toed crayfish by other unpretentious crayfish species;
- massive catch of crayfish for gastronomic purposes;
- human pollution of water sources.
An 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, crayfish, due to their abundance, became frequent guests on the tables of all segments of the population. Jews do not eat them, because. they are considered non-kosher animals.
Broad-toed crayfish protection
Internationally, the broad-clawed crayfish is listed on the IUCN Red List, Annex II of the Berne Convention, as a vulnerable species. This cancer is listed in the Red Books of Ukraine and Belarus. On the territory of our country, it is in the Red Book of the Leningrad Region.
The following actions can be classified as protective measures:
- constant monitoring of the state of surviving populations;
- assigning the status of protected areas to territories where a large number of broad-toed crayfish live;
- introducing strict quarantine for catching crayfish where crayfish plague has been detected;
- implementing licenses for catching a certain number of crustaceans;
- banning the discharge of various chemicals and pesticides into water bodies;
- treatment of fishing gear with special disinfectant solutions when moving to another body of water.
In the end, it is worth noting that it remains to be hoped that all these protective measures will bring a positive result, even if they do not increase the number of livestock cancer, at least make it stable. Do not forget that the broad-toed crayfish acts as a natural cleaner of various reservoirs, because it saves them from carrion. People also need to be more careful with water sources, keeping them clean, then the crayfish will feel at ease and wonderful.