Habits and Reproduction of Crabs They depend on the mother crab to give birth to young crabs. Every time, the mother crab will lay a large number of eggs, which can reach millions or more. After these eggs hatch in the abdomen of the mother crab, the larvae can leave the mother and float around with the coastal current. After molting several times, it grows into a big-eyed larva, and after molting several times, it grows into a young crab. The appearance of a young crab is almost the same as that of an adult crab, and it becomes a crab after molting several times. Most sea crabs are directly discharged into the sea without hatching after their eggs mature. \ x0d \ x0d \ The hard carapace on the crab can protect the crab from natural enemies, but the carapace will not swell with the growth of the body. Therefore, the growth of crabs is intermittent, that is, after a period of time, the body will continue to grow after the old shell falls off. The largest crab on the earth is the spider crab, with a foot width of 3.7 meters, and the smallest crab is the bean crab, with a diameter of less than half a centimeter. \x0d\ Crabs are small, but they are found in all aspects. After removing the hard shell of the crab, we can find that the body part of the crab is protected by a shell. These shield-like shells are called crustaceans by biologists. Crabs are symmetrical and can be divided into forehead area, eye area, heart area, liver area, stomach area, intestine area and gill area. The two sides of a crab are connected by appendages. The appendages of the head are called tentacles, which have the functions of touch and smell. Some appendages have the function of mouth, which is used to tear food and send it into the mouth. \x0d\ Crab chest has five pairs of appendages, which are called pectoral feet. A pair of appendages at the front end are equipped with powerful claws, which can be used for foraging. The other four pairs of appendages are crab feet. Crabs rely on these four pairs of appendages to walk and move. The way they walk is unique and interesting, and most of them walk sideways rather than straight. Except monks and crabs, they all walk straight. \x0d\ Crabs spend most of their time looking for food. They are not picky about food and eat everything they can. Small fish and shrimp are their favorite, but some crabs eat seaweed and even animal carcasses or plants. \x0d\ Crabs eat other animals, and other animals may also eat crabs. For example, humans regard crabs as delicious food. And waterfowl eat crabs! Some fish like to eat crab feet as much as humans. When young crabs and underage crabs float in the sea in groups, they may be devoured by other marine life, so crabs have to lay a lot of eggs when laying eggs. \x0d\ fiddler crabs are common crabs on the seashore. Why is it called fiddler crab? Because these crabs wave their claws as if they were waving in the tide, that's how they got the name "Zhao Chao". In addition, the giant claws of male fiddler crabs seem to play the violin, so they are also called fiddler crabs or fiddler crabs. \x0d\ Crab culture technology and disease prevention technology \x0d\ Eriocheir sinensis is a valuable freshwater product with delicious taste, rich nutrition and high economic value. \x0d\ Eriocheir sinensis is a large crustacean, belonging to the genus Eriocheir, and its body is divided into 2 1 section. Because the head and chest segments 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 \x0d\ 1. Biological characteristics and life history of Eriocheir sinensis \ x0d \/kloc-0 \ x0d \ Eriocheir sinensis is a crab that grows in fresh water and breeds 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 gonads are full, the male crabs have dense hair and thick bristles, and the abdomen of the female crabs completely covers the ventral surface of the head and breastplate, with long and dense bristles at the abdominal edge. \x0d\ The life span of river crabs 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. It takes the larvae to molt five times in a lifetime to become a big-eyed crab, and then it takes 13- 15 days to become an adult crab. It has only one reproductive cycle in its life, and its life will end at the end of reproduction. Generally speaking, a river crab is over. \x0d\ 2。 Living Habits \x0d\ (1) Cave Dwelling \x0d\ River crabs like to live in mud flats or caves on beaches in rivers and lakes, or hide in gravel and grass. Digging a hole is the instinct of the river crab, and it is also an adaptive way for the river crab to defend against enemy damage. 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. \x0d\ (2) Eriocheir sinensis has diverse feeding habits. Under natural conditions, it mainly eats aquatic plants and humus, and likes to eat animal carcasses, snails, mussels, worms and insects. Occasionally, I will prey on small fish and shrimp, and even swallow my own eggs. Sometimes, a dead fish will trigger a similar scramble for food. \x0d\ 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. \x0d\ (3) Molting and growth of Eriocheir sinensis \x0d\ The growth process of Eriocheir sinensis is accompanied by molting of larvae, young crabs or snails, and each molting of larvae is a metamorphosis, 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 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. \x0d\ Eriocheir sinensis needs to absorb a lot of water during molting, so its weight is obviously increased during molting. 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 one after another 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. \x0d\ 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. \x0d\ 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 superphosphate) are applied to the intensive crab pond every week (average water depth 1 m). The ratio of calcium and phosphorus must be considered in the compound feed for river crabs, and the ratio of calcium chloride to disodium hydrogen phosphate is 2: 1, so as to ensure the growth and development of river crabs. \x0d\ II。 Crab culture technology \x0d\ (I) Crab culture \x0d\ In order to improve the survival rate of young crabs and increase economic benefits, crab culture should be carried out 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. \x0d\ 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 the basic bait through the 80-mesh filter, 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. \x0d\ (II) Adult crab culture \x0d\ Adult crabs like the water environment with clean water quality, high transparency, abundant aquatic plants and rich bait, which is most suitable for the growth of river crabs. At present, it is mostly cultivated in ponds, lakes, rivers and rice fields. A brief introduction to the pond: \x0d\ 1, pond conditions \x0d\ Clay, sandy soil or sub-sandy soil with abundant water, convenient water intake and drainage, good water pollution and good aeration 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. \x0d\ 2。 The natural yield of transplanted aquatic plants \x0d\ Eriocheir sinensis mainly depends on the number of aquatic plants and benthic organisms (food 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. Aquatic plants mainly include duckweed, red duckweed, water hyacinth, water hyacinth, verticillium, Ceratophyllum, Sophora alopecuroides and Alternanthera philoxeroides. Attention should be paid to disinfection and prevention when transplanting. \x0d\ 3。 Escape prevention facilities \x0d\ Escape prevention facilities mostly use plastic film, and some use cement board, depending on their own situation. \x0d\ 4。 Disinfection of pond cleaning \x0d\ Generally, the pond is disinfected with quicklime half a month before the seedlings are released, and the dosage is 75kg 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. \x0d\ 5. Release seedlings \x0d\ Crab seedlings produced in the Yangtze River system are the best, requiring neat specifications, complete steps, strong physique, active crawling, and no injury or disease. \x0d\ seedlings and density. Pay attention to the 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. \x0d\ Density: At present, polyculture is the main method, especially fish, shrimp and crab polyculture, 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. \x0d\ 6。 Daily management \x0d\ (1) Feeding: The whole process of intensive culture in ponds mainly depends on manual feeding, so the type, quality and quantity of feed have great influence on the growth and development of river crabs. When feeding, we should adhere to the principle of reasonable combination of fine, green and coarse, with animal concentrate accounting for 40% and aquatic plants accounting for 35%. (2) Animals: small miscellaneous fish in sea and fresh water, corpses 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. Commodity feed: sweet potato, hemp potato, grain, bran, feed bran, etc. \x0d\ Like pond culture, the feeding method of river crabs is "four observations and four determinations", that is, watching seasons, weather, water quality and crab activities, regularly, regularly, qualitatively and quantitatively. \x0d\ It depends on the season: In spring, young crabs should be fed some live animal feed. In the middle growth period of river crab, especially from May to August, the amount of animal feed should be appropriately increased, but plant feed is the main one. In the later stage, the river crab needs a lot of nutrition to meet the gonad development, so it is necessary to feed more animal feed to make the river crab gain weight and taste delicious. Feed distribution is generally 40% from March to June. \x0d\ Look at the weather: feed more in sunny days and less in rainy days. When the weather is sultry, you can stop feeding before the windless shower, and in foggy days, wait until the fog closes before feeding. \x0d\ Look at the water quality: the water quality is clear, the feeding is normal, and the water quality is strong, so the feeding should be reduced appropriately and the water should be changed in time. \x0d\ Look at the activity of crabs: Generally, they are eaten up the next morning after feeding. If the feeding amount is appropriate, it means that crabs have a bad appetite or too many. Therefore, it is necessary to analyze the reasons in time, reduce the feeding amount, and appropriately increase the feeding amount during molting. \x0d\ Timing: Eriocheir sinensis has the habit of lying in the daytime and coming out at night. It goes out for food at night and feeds twice at eight or nine in the morning and in the afternoon and evening. The feeding amount at night is 60-70% of the whole day feeding amount. \x0d\ Fixed point: The feed to be fed should have fixed food, and the feed should be scattered on the feed table or on the slope near the shallow water level, so as to observe the feeding and activities of the river crab and increase or decrease the feed at any time. Chinese mitten-handed crabs have a strong competition for food, so it is necessary to set up more points so that Chinese mitten-handed crabs can eat evenly and avoid killing each other because some of them are small or weak and can't compete for feed. \x0d\ Qualitative judgment: Eriocheir sinensis is sensitive to fragrant, sweet, bitter, salty, smelly and other flavors, and its feed must be fresh, palatable and rich in protein. \x0d\ Quantification: "If you don't eat fish for one day, it won't be bad for three days", and so does the river crab. This requires that the feeding amount should be determined according to the size, density, different seasons, weather and activities of river crabs. Generally, the daily feeding amount is 8- 10% of the crab weight in the pond. If the feeding amount is small, it can only maintain life, and if it exceeds the timely range, it will also affect growth and increase feed coefficient. \x0d\ Feed with animal and plant feeds, such as forage and grain in the morning and mussels, snails and silkworm chrysalis in the afternoon. Avoid feeding a single feed for a long time, otherwise it will cause anorexia, low feed utilization rate, affect growth and small specifications. \x0d\ (2) Water quality management: Eriocheir sinensis requires higher water quality than fish and is more sensitive to polluted water. The pond water quality is good, which is beneficial to the growth and development of Eriocheir sinensis, and the meat is delicious. The PH value of the crab pond water should be kept at 7-9, preferably 7.5-8.5, and the dissolved oxygen in the pond should be kept above 5MG/ 1 and below 5MG/. Crab will die when it is below 2MG/ 1. Adjust the PH value of the pool water. At present, the water quality of newly dug ponds is mostly acidic, so it is necessary to spray quicklime slurry regularly to improve the water quality, which can improve the utilization rate of feed for crabs and help them molt smoothly. Generally once a month in spring, once a day in summer and autumn 15-20, and the water depth is 65438 per mu. \x0d\ Pay attention to changing water frequently to keep the water level stable. Change the water once a week in spring and once every three days in summer. In case of continuous high temperature, change the water every day. In autumn, the weather is hot and sultry, and the water quality tends to deteriorate. Pay special attention to changing water, once every two days, accounting for 1/3 of the total water area. \x0d\ River crabs are not tolerant of fat water. In order to control the water quality and keep it from becoming fat, 200-300 species of silver carp are planted per mu, and aquatic plants are planted around the crab pond. \x0d\ Different seasons require different water levels in crab ponds. In order to raise the water temperature and promote the growth of river crabs in spring, the water level can be controlled at 0.5—0.7m, the water temperature is higher in summer and autumn, and the depth of the pond should be kept at1-1.5m. \ x0d \ (3) Escape prevention: special personnel are on duty to patrol the embankment, especially when it rains and the weather changes. \x0d\ (4) Patrol the pond: observe the color of the water, pay attention to the activities of crabs, do not harm the river crabs, and keep the water environment stable. When the gonads are well developed and the price is appropriate, the pool water can be released and fished up.