Culture technology of river crab

Eriocheir sinensis, the scientific name of Eriocheir sinensis, is a valuable freshwater product with delicious taste, rich nutrition and high economic value. River crab belongs to crustacean, mitten crab genus, is a large crustacean, the body is divided into 21 segments, because the head and chest segments heal each other, so the whole body is divided into two parts: head, chest and abdomen. The adult crab has dark green back and gray ventral face. The average length of head and chest nail is 6-7cm and the width of 7.5cm is wide.

The life history of river crab

River crabs are crabs that grow in fresh water and breed in sea water. They are all young crabs before reproductive migration. Because of their yellow shell color and vulgar second "yellow crabs", their gonads are very small and basically undeveloped, and the weight of the liver is much larger than that of the gonads. When it finished molting for the last time, it developed into a "green crab". The overbought dark green gonad developed well, the male crab had dense villi and long bristles, and the abdomen of the female crab completely covered the ventral surface of the head and chest nail, and the bristles on the edge of the abdomen were long and dense.

The life of river crab is short. In its life history, it goes through several stages, such as flea larva, big-eyed larva, young crab and adult crab. It needs larvae to molt into big-eyed larvae five times in its life, and then molts to become adult crabs after 13 minutes of molting for 15 days. It has only one reproductive cycle in its life, and the life span of river crabs ends at the end of reproduction. Generally speaking, the life span of river crabs is 3 weeks old.

The living habits of River Crab

1. Cave dwelling

River crabs like to live in caves on muddy banks or shoals of rivers and lakes, or hide in gravel and water plants. River crab burrowing is its instinct, and it is not an adaptive way for river crab to defend against enemy damage. River crabs generally choose to dig holes on steep banks with hard soil, with a slope of 0.2 or 0.3, rarely on gentle slopes below 1.5-2.5, let alone on flat ground. This provides a basis for the construction of our culture ponds.

2. Eating habits

The eating habits of river crabs are very miscellaneous. Under natural conditions, they mainly eat water plants and humus, eat animal carcasses, and also like to eat snails, clams, worms, insects, and occasionally cannibalize each other when there is a lack of food for small fish and shrimps. They even swallow the eggs they hold, and sometimes they compete for food of the same kind because of a dead fish. in general, it is easy for river crabs to obtain plant food, which often constitutes the main component of crab stomach food. There is also some sediment in the crab's stomach, which is a sign that the crab feeds on benthos and humus.

River crabs usually hide in their holes during the day and go out to look for food at night. On land, river crabs do not eat much and often drag the food on the shore to the water or to the edge of the cave before feeding. During the year, except for the low temperature jellyfish, the crabs do not eat temporarily, even if they migrate in winter, they also eat as usual. When the water quality is good, the water temperature is suitable, and the bait is abundant, the river crab has a large amount of food, and it can continuously prey on several snails in one day and night. the soft-shell crab that has just molted its skin, and the disabled individual is often harmed, but the river crab has a strong ability to endure hunger. If you don't eat for 10 days or even half a month, the river crab will not starve to death. Under the condition of artificial culture, according to the needs of the growth and development of river crab, mastering the structure of "fine-coarse-fine" in feeding feed is beneficial to the growth of river crab.

3. Molting and growth

The growth process of river crab is accompanied by the molting of larvae, young crabs or adult snails. every molting of the larvae is metamorphosis, which is divided into one stage. From the big-eyed larva molting to the first stage young crab, each time it molts its body length and weight increases by leaps and bounds. From the body weight of each big-eyed body 6-7mg to 250g, the crab needs to molt at least dozens of times, and each molting is going through a survival barrier.

During molting, the river crab needs to absorb a lot of water, so the quality increases obviously in the process of molting, but in the later growth, the loss of water is slow, and is gradually replaced by tissue growth, and the growth rate of river crab is restricted by environmental conditions, especially water temperature and bait. In general, the molting times of early young crabs are more frequent, and the big-eyed larvae that just entered the lake become the second and third stages of young crabs every 5 and 10 days after that. With the continuous growth, the molting interval is gradually prolonged. If the environmental conditions are bad, molting growth stops, which is also the reason why individuals of the same age differ greatly in body shape under different conditions.

The growth of river crab is closely related to calcium and phosphorus in water and bait. Relevant experiments have shown that the body weight of soft-shell crabs that have just molted is 30% more than that before molting, and the weight is 40% higher than that before molting. During this period, it takes as much as an hour, or a few minutes less, and relies on the gills to absorb a large amount of water and inorganic salts in the water. In natural ponds or lakes, soft-shell crabs become hard in 2 days. If the soft-shell crab is raised in distilled water, the ability of absorbing calcium ion in water is stronger than that of calcium and phosphorus in formula feed. The total amount of calcium in the shell is equal to that in the body on the eve of molting, and the total amount of phosphorus in the body is 52.2 times higher than that in the shell.

In order to cooperate with the growth and molting of river crabs, 5kg of calcium chloride was applied per mu (average water depth of 1m) per mu in intensive crab ponds. The ratio of calcium and phosphorus must be considered in the formula feed of sodium hydrogen phosphate 2.5kg (or quicklime or calcium superphosphate). The disodium hydrogen ratio of calcium chloride and phosphorus is 2:1 in order to ensure the material needs of crab growth and molting.

Juvenile crab rearing

In order to improve the survival of young crabs and increase economic benefits, we must first cultivate buckle crabs. In order to make the big-eyed larvae reach commercial crabs, the temporary culture technology in plastic greenhouse is mostly used at present. Choose ponds with good water quality, adequate water sources, convenient injection and drainage, no leakage, no water seepage and less silt, the area should not be too large, the water depth should not exceed 1.2 meters, the pond shape should be good in east-west direction and sufficient sunshine, and the construction of greenhouse can refer to the construction method of agricultural vegetable greenhouse.

For 20 days before releasing crab fry, sprinkle 75 kilograms of quicklime per mu for disinfection. After the medicine disappears, use 80 mesh filter to enter the water, cultivate basic bait, transplant aquatic plants (must be strictly sterilized), and set up necessary escape prevention facilities. Crab seedlings can be shallower when entering the pond. It is beneficial to improve the water temperature and the growth of algae and aquatic plants in the water. Feed 2mi 3 times a day, feed soybean milk, fish, shrimp paste, etc., and feed more in the surrounding shallow areas. The bait should be calculated according to 4% of the body weight, and pay attention to the weather, water sanctions, individual growth, and the number of bait creatures at any time. With the growth of young crabs, some plant bait should also be added, such as duckweed and other high-quality aquatic plants, pay attention to the regulation of water quality in daily management, grasp the fat and cool water quality, and change water frequently and less, so as not to cause drastic changes in water temperature and water level. After about 2 months of cultivation, the buckle crab can be achieved.

Adult crab culture

Adult crabs like the water environment with clean water quality and greater transparency, with numerous water plants and rich bait, and the river crab is the most suitable for growth. At present, most of them are cultured in ponds, lakes, river swings and rice fields. Here is a brief introduction to ponds:

1. Pond conditions: sufficient water source, convenient entry and drainage, good water pollution, clay, sandy soil or sub-sandy soil, good ventilation, which is conducive to the growth and reproduction of aquatic plants and benthic insects, snail clams, water earthworms, etc., the old pond should be thoroughly desilted, the silt should not exceed 20cm, and the pond area should not be too small. The water depth of the pond is maintained at about 0.6fu 1.5 meters all the year round, and the depth varies everywhere, and the shallowest 10cm can be made in the pond slightly above the surface of the water, that is, Crab Island, on which aquatic plants can be transplanted, the pond is not too steep, and the slope ratio is generally below 1RU 1.5, otherwise, the river crab is easy to dig holes and is not conducive to climbing out of the water at night. Artificial caves can also be built.

2. Transplanting aquatic plants: the natural yield of river crabs mainly depends on the number of aquatic plants and benthos (bait organisms) in the water area. It is an indispensable technical measure to plant aquatic plants in the process of breeding. In addition to supplying vitamin for crabs, growing aquatic plants can also support each other's fighting and concealment, which is an effective measure to improve the survival rate of river crabs in each period. in addition, it can also absorb harmful ammonia nitrogen, carbon dioxide, organic matter, release oxygen and stabilize water quality. The masses often say, "crab size, look at water plants." Therefore, great efforts must be made to plant good aquatic plants for river crab culture in ponds. The main types of aquatic plants are duckweed, Manjianghong, water hyacinth, water floating lotus, verticillium verticillata, goldfish algae, bitter grass, water peanut, etc., pay attention to disinfection and prevention when transplanting.

3, anti-escape facilities: escape prevention facilities mostly use plastic film, but also use cement board, depending on their respective conditions.

4, clear pond disinfection: generally disinfect the pond with monthly quicklime before releasing seedlings, the dosage is 75 kg per mu. On the one hand, it can kill enemy organisms, on the other hand, it can improve the bottom of the pond, increase the content of calcium ions in water, and promote the molting growth of river crabs. Fertilize in time after receiving water, cultivate algae and basic bait, transparency is generally maintained in 40-50cm, if tadpoles or frog eggs are found to be removed in time, so as not to compete for food and harm young crabs.

5, release seedlings: seedling selection and purchase of crab seedlings produced in the Yangtze River system is the best, requiring neat specifications, complete steps, strong physique, active crawling, no injury and no disease. Seedlings purchased from other places can not be put directly into the pond. Soak in water for 3 minutes, take out and place for 10 minutes, repeat 2murl 3 times. After the young crabs gradually absorb enough water and adapt to the water temperature, put them into the pond, which can improve the survival rate. Density: at present, most of them are mixed culture, especially the mixed culture of fish, shrimp and crabs, the economic benefit will be higher. The density can be controlled within 1500 / mu and the specification is 120mur150 / kg. If the conditions are poor or shrimp culture can appropriately reduce the amount of seedlings.

Daily management

The feeding method of river crabs is like that of fish farming in ponds, achieving "four looks and four decisions", that is, shield season, weather, water quality, crab activity, timing, fixed point, quality, and quantity.

1. Baiting: the whole process of intensive culture in the pond mainly depends on artificial feeding, so the type, quality and amount of feed have a great impact on the growth and development of river crabs. The principle of reasonable matching of concentrate, green and coarse should be adhered to when feeding. Animal concentrate accounts for 40%, aquatic plants account for 35%, and other plant feeds account for 25%. There are three main types of feed:

① full-price special formula feed for river crab

② animal nature: Marine and freshwater fish, carcasses, snails, mussels, blood of livestock and poultry, fish meal, silkworm pupa, etc.

③ plant: aquatic plants, duckweed, water peanuts, bitter grass, verticillata, etc., commercial feed category: potato, Ma Ling potato, cereals, wheat bran, material bran and so on.

2. Depending on the season: young crabs in spring should be fed some live animal feed. In the middle growth period of river crabs, especially from May to August, it is necessary to appropriately increase the amount of animal feed, but mainly plant feed, and in the later stage, river crabs need a lot of nutrition to meet gonadal development. Animal feed should be fed more, so that the weight of river crabs is increased, the meat is delicious, and the feed distribution is generally 40% from March to June. From July to October, 60% of the water temperature is below 10 degrees Celsius, the activity of the crab is less, and the food intake is small, so it can be fed less, once every other day, and when the water temperature is 3 mi 5 degrees Celsius, there is no need to feed.

3. Look at the weather: feed more when the weather is sunny and less on cloudy and rainy days. In muggy weather, you can stop feeding before there is no wind and showers. On foggy days, you can feed again after the fog ends.

4. Look at the water quality: the water quality is clear, the bait can be fed normally, the water quality is strong, the feeding should be reduced appropriately, and the water should be changed in time.

5, look at the activity of crabs: generally eat up the next morning after feeding, the amount of bait is appropriate, eat not only, indicating that the appetite of river crabs is not exuberant or the number is too much, the reasons should be analyzed in time, the amount of feeding should be reduced, and the feeding amount of crabs should be increased appropriately during molting.

6. timing: River crabs have the habit of sleeping during the day and going out at night to look for food at night. Feeding is carried out at 8 am, 9 o'clock in the morning and in the afternoon in the evening, and the evening feeding rate is 60% of the daily feed volume.

7. fixed point: the feed should have fixed food, and the feed should be scattered on the feed table or choose on the slope near the shallow water line, in order to observe the feeding and activity of river crabs, and increase or decrease the feed at any time. River crabs have a strong competition for food, so it is necessary to set up more points to make river crabs eat evenly, so as to avoid some of them being unable to compete for feed and causing each other to kill each other.

8. quality: River crabs are sensitive to fragrant, sweet, bitter, salty, smelly and other tastes, and the feed must be fresh and palatable and rich in protein.

9. Quantitative: "if you don't eat fish for one day, you won't grow for three days." similarly, river crabs are required to determine the amount of feeding according to their size, density, different seasons, weather, and activities. Generally, the daily feeding amount is 8% of the body weight of pond crabs. A small amount of feeding can only maintain life, beyond the timely range also affects growth, but also increases the feed coefficient.

Bait should be matched with animal and plant feed, such as forage and cereals in the morning and mussel meat, snails and silkworm pupae in the afternoon.