Crab culture technology?

The scientific name of Eriocheir sinensis is Eriocheir sinensis, which is delicious, nutritious and of high economic value. It is a valuable freshwater product.

Eriocheir sinensis is a large crustacean belonging to the genus Eriocheir, which is divided into 2 1 section. Because the head and chest heal each other, the whole body is divided into two parts: head, chest and abdomen. Adult crabs have a dark green back and a gray belly. The head breastplate is 6-7 cm long and 7.5 cm wide on average.

1. Biological characteristics of Eriocheir sinensis

1, life history

River crabs are crabs that grow in fresh water and breed in seawater. Before the reproductive migration, they were all young crabs. Because of their yellow shells, they are called "yellow crabs". Their gonads are very small and basically undeveloped, and the weight of the liver is far greater than that of the gonads. When it molts for the last time, it will develop into a "blue crab". The purchased dark green gonad is full, the male crab has dense hair and thick bristles, the female crab completely covers the ventral surface of the head and breastplate, and the bristles on the ventral edge are long and dense.

The life span of Eriocheir sinensis is very short. In its life history, it has gone through several stages, such as flea larva, megalopa larva, young crab and adult crab. In its lifetime, it takes 5 times for a larva to molt into a big-eyed larva, and then it takes 13- 15 days to molt into an adult crab. It has only one reproductive cycle in its life, and when reproduction ends, its life will also end. Generally speaking, the life span of Eriocheir sinensis is 65438 years.

2. Living habits

(1) caves

Eriocheir sinensis likes to live in mud flats or caves on the beach in rivers and lakes, or hide in gravel and aquatic plants. It is an instinct for the river crab to dig a hole, which is not an adaptive way for the river crab to defend itself from the enemy. Crabs usually dig holes on steep slopes with hard soil, and the bank slope is 1:0.2 or 1:0.3. They rarely dig holes on gentle slopes below 1: 1.5-2.5, let alone on flat land. This provides a basis for the construction of aquaculture ponds in China.

② Eating habits

Eriocheir sinensis has a variety of feeding habits. Under natural conditions, it mainly eats aquatic plants and humus, likes to eat animal carcasses, and also likes to eat snails, mussels, worms and insects. Occasionally, it also preys on small fish and shrimp. When food is scarce, it will even devour its own eggs, and sometimes it will cause similar food competition because of a dead fish. Under normal circumstances, Eriocheir sinensis can easily get plant food, which often constitutes the main component of crab stomach food.

River crabs usually hide in caves during the day and go out for food at night. On land, river crabs don't eat much, and often drag the food on the shore to the underwater or the edge of the cave before eating. On the anniversary, river crabs eat as usual even when they migrate in winter, but they don't eat at low temperature for the time being. When the water quality is good, the water temperature is suitable and the bait is sufficient, the river crab can eat a lot. It can prey on several kinds of snails, soft-shelled crabs that have just molted and individuals that have been disabled, but river crabs have strong hunger tolerance. If it doesn't eat for 10 days or even half a month, the river crab won't starve to death. Under the condition of artificial culture, it is beneficial to master the structure of "fine-coarse-fine" when feeding the bait according to the needs of the growth and development of river crabs.

(3) molting and growth of Eriocheir sinensis

The growth process of Eriocheir sinensis is accompanied by the molting of larvae, young crabs or adult snails. Larvae metamorphoses every time they molt, which is divided into one stage. From the molting of megalopa to the first stage of juvenile crab, the body length and weight of each megalopa will advance by leaps and bounds every time it molts. The weight of each crab will gradually increase from 6-7 mg to 250 g, which requires at least dozens of molts, and each molt will pass through the survival barrier.

Eriocheir sinensis needs to absorb a lot of water during molting, so its mass is obviously increased. In the later stage of growth, water loss is slow and gradually replaced by tissue growth. The growth rate of Eriocheir sinensis is restricted by environmental conditions, especially water temperature and bait. Usually, early young crabs often shed their skins. The megalopa larvae just entering the lake will shed their skin every 5-7 days and 7- 10 days to form the second and third larvae. With the continuous growth, the molting interval will be extended. If the environmental conditions are not good, the molting growth will stop, which is also the reason for the great difference in body shape between individuals of the same age and under different conditions.

The growth of Eriocheir sinensis is closely related to calcium and phosphorus in water and food. Related experiments show that the body weight of soft-shelled crabs increases by 30%-40% just after molting, which lasts for 1 hour, and relies on gills to absorb a lot of water and inorganic salts in water for at least a few minutes. In natural ponds or lakes, the shells of soft-shelled crabs become hard after 1-2 days. If soft-shelled crabs are raised in distilled water, their ability to absorb calcium ions in water is stronger than that of calcium and phosphorus in compound feed. Before molting, the total amount of calcium in the shell is required to be equal to that in the body, and the total amount of phosphorus in the body is 52.2 times that in the shell.

In order to cooperate with the growth and molting of Eriocheir sinensis, 5 kg of calcium chloride and 2.5 kg of disodium hydrogen phosphate (or calcium lime or calcium superphosphate) were applied per mu (average water depth 1 m) in intensive crab ponds every week, and the ratio of calcium chloride to disodium hydrogen phosphate was 2: 1, considering the calcium-phosphorus ratio, so as to ensure the material needs of the growth and molting of Eriocheir sinensis.

Second, the river crab culture technology

① Breeding of Eriocheir sinensis

In order to improve the survival rate of young crabs and increase economic benefits, it is necessary to cultivate crabs first. At present, in order to make the big-eyed larvae reach the commercial crab, most of them adopt temporary rearing technology in plastic greenhouse. Choose a water source with good water quality and sufficient water; Note: ponds with convenient drainage, no water leakage, no water seepage and little silt should not be too large, and the water depth should not exceed1.2m. The east-west direction of the pond is good, and the sunshine is sufficient. Please refer to the construction method of agricultural vegetable greenhouse for the construction of greenhouse.

15- 20 days before the release of crab seedlings, 75 kg of quicklime should be sprinkled and disinfected per mu. After the medicinal properties disappear, we should feed water through an 80-mesh sieve to cultivate basic bait, transplant aquatic plants (which must be strictly disinfected), and set up necessary escape prevention facilities. Crab seedlings can be shallower when they enter the pool. Conducive to improving the water temperature and the growth of algae and aquatic plants in the water. Feed bait 2-3 times a day, such as soybean milk, fish and shrimp paste. And feed more in the surrounding shallow water, and feed at 4% of the body weight, and always pay attention to the weather, water sanctions, individual growth and the number of organisms competing for food. With the growth of young crabs, we should also add some plant bait, such as duckweed and other high-quality aquatic plants. In daily management, we should pay attention to water quality regulation, grasp that water quality should be fat and cool, 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, crabs can be detained.

② Adult crab culture

Adult crabs like the water environment with clear water quality, great transparency, rich aquatic plants and rich bait, which is most suitable for the growth of river crabs. At present, most of them are cultivated in ponds, lakes, rivers and rice fields. Now give priority to with the pond for a brief introduction:

1, pond conditions

Adequate water resources, convenient water intake and drainage, and good water pollution are conducive to the growth and reproduction of clay, sandy soil or sub-sandy soil such as aquatic plants, benthic insects, snails and water worms. The old pond should be completely dredged, the silt should not exceed 20 cm, and the pond area should not be too small. The water depth of the pond is kept at about 0.6- 1.5m all the year round, and varies from place to place, with the shallowest point being 10cm. You can build several mounds slightly above the water surface in the pond, that is, crab island, where aquatic plants can be transplanted. The pond should not be too steep, and the slope ratio is generally below 1: 1.5, otherwise it is easy to grow river crabs. You can also build artificial caves.

2. Transplant aquatic plants

The natural yield of Eriocheir sinensis mainly depends on the number of aquatic plants and benthic organisms (bait organisms) in the waters. It is an indispensable technical measure to plant aquatic plants well in the process of breeding. Planting aquatic plants can not only feed crabs and supplement vitamins for ten days, but also support fighting and concealment, which is a powerful measure to improve the survival rate of river crabs in each period. In addition, it can absorb harmful ammonia nitrogen, carbon dioxide and organic substances in the pool, release oxygen and stabilize water quality. The masses often say that "the size of crabs depends on aquatic plants." Therefore, for river crabs cultured in ponds, great efforts should be made to plant aquatic plants. Our aquatic plants mainly include duckweed, red duckweed, water hyacinth, water hyacinth, black algae, Ceratophyllum, Sophora alopecuroides, Alternanthera philoxeroides and so on. Attention should be paid to disinfection and prevention when transplanting.

3. Escape prevention facilities

Escape prevention facilities mostly use plastic film, but also use cement board, depending on their own situation.

4, pond cleaning and disinfection

Generally, the pond is disinfected with quicklime half a month before the seedlings are released, and the dosage is 75 kg per mu. On the one hand, it can kill pests, on the other hand, it can improve the bottom of the pond, increase the content of calcium ions in the water and promote the molting growth of Eriocheir sinensis. Fertilize in time after receiving water, cultivate algae and basic bait, and the transparency should generally be maintained at 40-50 cm. If tadpoles or frog eggs are found, they should be removed in time to avoid competing for food and hurting young crabs.

5, put the seedlings

Crab seedlings produced in the Yangtze River system are excellent for seed selection, requiring neat specifications, complete steps, strong physique, active crawling and no injury or disease.

Sowing and density, pay attention to temperature difference when sowing. Fish fry bought from other places can't be directly put into the pond. They should be soaked in clear water for 2-3 minutes, then taken out and put into the pond 10 minute, and repeated for 2-3 times. After the young crabs gradually absorb enough water and adapt to the water temperature, they should be put into the pond, which can improve the survival rate.

Density: At present, it is mostly polyculture, especially polyculture of fish, shrimp and crab, which will bring higher economic benefits. The density can be controlled within 1500/mu, and the specification is120-150/kg. If the conditions are poor or shrimp farming is the main thing, the amount of seedlings released can be reduced appropriately.

6. Daily management

(1) Feeding: The whole process of intensive culture in ponds mainly depends on artificial feeding, so the type and quality of feed have a great influence on the growth and development of river crabs. When feeding, we should adhere to the principle of reasonable collocation of fine, green and coarse, with animal concentrate accounting for 40%, aquatic plants accounting for 35% and other plant feeds accounting for 25%. There are mainly three kinds of feed (1)(2) animals: small miscellaneous fish in seawater and fresh water, carcasses of various animals, snails, mussels, blood of livestock and poultry, fish meal, silkworm chrysalis, etc. ; (3) Botany: aquatic plants, duckweed, Alternanthera philoxeroides, black algae, etc. And commercial feeds: sweet potato, hemp potato, cereal, bran, feed bran, etc.