Eriocheir sinensis is a large crustacean belonging to the genus Eriocheir, which is divided into 2 1 node. Because the head and chest segments are mutually healed, the whole body is divided into two parts: head, chest and abdomen. Adult crabs have a dark green back and a gray belly. The average length of the head breastplate is 6-7 cm and the width is 7.5 cm.
1. Biological characteristics of Eriocheir sinensis
1, life history
River crabs are crabs that grow in fresh water and breed in seawater. Before reproductive migration, they were all young crabs. Because their shells are yellow, 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 develops 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 to go 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 megalopa, and then it takes 13- 15 days to molt into a crab. It has only one reproductive cycle in its life, and when reproduction ends, its life ends. Generally speaking, the life span of Eriocheir sinensis is 65438.
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 a river crab to dig a hole, and it is not an adaptive way for a river crab to defend itself from the enemy. Crabs usually burrow on steep slopes with hard soil, with bank slopes of 1:0.2 or 1:0.3, and rarely burrow 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 they prey on small fish and shrimp. When food is scarce, it will even devour the eggs it holds, 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 if they migrate in winter, but they don't eat low temperature for the time being. When the water quality is good, the water temperature is suitable and the bait is rich, the river crab can eat a lot. It can prey on several snails, newly molted soft-shelled crabs and disabled individuals, 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 "fine-coarse-fine" structure of feeding 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. Every time a larva molts and metamorphoses, it 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 big-eyed crab will gradually increase from 6-7 mg to 250 g, and it needs at least dozens of molts, and each molt must pass the survival barrier.
Eriocheir sinensis needs to absorb a lot of water during molting, so its weight 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 just entering the lake will molt once every 5-7 days and 7- 10 days to form the second and third stage larvae. With continuous growth, the molting interval will be extended one after another. If the environmental conditions are not good, the molting growth will stop, which is also the reason why individuals of the same age have great differences in body shape under different conditions.
The growth of Eriocheir sinensis is closely related to calcium and phosphorus in water and food. Related experiments show that the weight of newly molted soft-shelled crabs is increased by 30%-40% compared with that before molting, and this period is as long as 1 hour, and it takes at least a few minutes, relying on gills to absorb a lot of water and inorganic salts in water. 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 quicklime or calcium superphosphate) were applied per mu (average water depth 1 m) in intensive crab ponds every week. The ratio of calcium to phosphorus must be considered in the compound feed of Eriocheir sinensis, and the ratio of calcium chloride to disodium hydrogen phosphate is 2: 1, so as to ensure the material needs of Eriocheir sinensis for growth and molting.
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, crabs should be raised 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 one with good water quality and sufficient water resources; Note: The pond with convenient drainage, no water leakage, no water seepage and little silt should not be too large, the water depth should not exceed 1.2m, 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 crab seedlings are released, 75 kilograms of quicklime should be sprinkled on each mu for disinfection. After the medicinal properties disappear, it is necessary to feed water with 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, shrimp paste, etc. , and feed in the surrounding shallow waters, and feed at 4% of the body weight, and always pay attention to the weather, water quality 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, change water frequently, and change water 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 clear and transparent water environment, rich in aquatic plants and rich in bait, which is most suitable for the growth of river crabs. At present, it is mostly cultivated in ponds, lakes, rivers and rice fields. Now give priority to with the pond for a brief introduction:
1, pond conditions
Clay, sandy soil or sub-sandy soil with sufficient water, convenient water intake and drainage, good water pollution and good ventilation are beneficial to the growth and reproduction of aquatic plants, benthic insects, snails and water worms. The old pond should be thoroughly dredged, the silt should not exceed 20cm, 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 10cm. Several mounds slightly above the water surface can be built 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 the river crabs will grow easily. 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. In the process of aquaculture, it is an indispensable technical measure to plant aquatic plants well. 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 various periods. In addition, it can absorb harmful ammonia nitrogen, carbon dioxide and organic matter in the pool, release oxygen and stabilize water quality. The masses often say that "the size of crabs depends on aquatic plants." Therefore, river crabs cultured in ponds should make great efforts to plant aquatic plants. Our aquatic plants mainly include duckweed, red duckweed, water hyacinth, water hyacinth, black algae, Ceratophyllum, Sophora alopecuroides, water peanuts 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 useful 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 to cultivate algae and basic bait, and the transparency is generally maintained at 40-50 cm. If tadpoles or frog eggs are found, they should be taken out in time to avoid competing for food and hurting young crabs.
5, put the seedlings
Crab seedlings produced in the Yangtze River system are the best seed selection, requiring neat specifications, complete steps, strong physique, active crawling and no injuries.
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 water for 2-3 minutes, taken out and put into the pond 10 minute, and repeated for 2-3 times. Young crabs gradually absorb enough water, adapt to the water temperature, and then put them 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 crabs/mu, and the specification is120-150 crabs/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 feed accounting for 25%. There are three main types of feed: ① ② animals: small miscellaneous fish in seawater and fresh water, corpses of various animals, snails, mussels, blood of livestock and poultry, fish meal, silkworm chrysalis and so on. ; (3) Botany: aquatic plants, duckweed, Alternanthera philoxeroides, black algae, etc. Commodity feed: sweet potato, hemp potato, grain, bran, feed bran, etc.