Crab Pond Construction Crab ponds are built in calm, fresh water-filled, unpolluted inner bays and are located on sand mudflats with a certain slope below the mid-tide line. The depth of the crab ponds requires 0.8-1 meter of water during dry tides. The area is mostly 2-5 acres. The pond embankment is made up of three-segment soil, or stones, and a cement-filled straight bank with no gradient. If the earth embankment, it is necessary to block or insert bamboo foil to prevent the crabs from escaping.
Seedlings stocking and stocking time The stocking of blue crabs can be divided into two main types: 1. The juvenile crabs are used as seedlings, and they are raised from small to large. They have to go through the whole process of breeding from young crabs to commercial crabs. 2. Use big size crabs as seedlings for fattening purposes. Green crabs can be stocked throughout the year in southern China, but the length of time required is not only influenced by water temperature, salinity, and diet, but also directly related to seedling specifications. With juvenile crabs as seedlings, it usually takes a few months to harvest. For the purpose of fattening, the feeding time is generally 20-40 days, and the harvest can be harvested in as early as 10 days. In February-March, the reproductive gonads of the crabs are the fastest and can be harvested 18 days after stocking; they need to be kept for 20 days in April-May; after 20 months, they need more than 20 days to be harvested; and between July and September, due to the hot weather If the water temperature is too high, the growth of the crab is not good, and it is easy to die; the water temperature is low in October and December, and it will take 30-40 days to harvest.
Second, stocking density Density of blue crabs, according to the season, individual size, bait and crab ponds and other conditions to be set. If the stocking density is too high, the phenomenon of mutual clamping will easily occur due to crowding, causing casualties. If the stocking density is too small, it will waste water and affect the efficiency. During April-August, as the temperature rises day by day and it is the rainy season, the water temperature and the proportion change greatly, and it is easy to cause the death of the green crab. Therefore, the stocking density should be appropriately reduced. For more than 150 grams of crabs, generally about 4.5 eggs per square meter. From autumn to March in the following year, the water temperature is relatively low and the transparency is high. It is advisable to store more than 6-7.5 eggs per square meter. If the crab is less than 150 grams, and in particular only 25-50 grams of juvenile crabs, the stocking density may be appropriately increased. If the crabs from the big eye larvae come from the shell, the stocking density can be stocked with reference to the stocking density of shrimp, but after a period of stocking needs to be divided into pools. For ease of management, during stocking, it is best to stockseed according to the size of the seedlings. The general regulations are as follows: female crabs, crabs, unfertilized crabs, male crabs, 25-75 grams of young crabs, and 100-150 grams of small crabs. Pool feeding. If the supply of seedlings is insufficient, the stocking requirements cannot be met in time and they can be stocked in batches.
Feeding Technology I. Types of bait Green crab is mainly carnivorous, but sometimes it also feeds some plant foods (such as seaweed shoots and seaweeds). Used as a blue crab bait: small shellfish (such as crab snails, red meat blue clams, Chinese green clams, duckbills, oysters, oysters, or land snails), as well as small fish and shrimp , small crabs and so on. Practice has proved that the use of crab snails and oysters as bait, feeding well. From August to October each year, crab snails are very fat. Green crabs are the most favorite and are often fed. The blue crab's ovary matures rapidly, and the meat is plump and of good quality. However, fish and shellfish are generally used as a mixed bait. All localities should choose the types of bait according to actual conditions and require fresh bait.
Second, the amount of feed bait amount and temperature and other environmental conditions are closely related. Blue crabs in the water temperature 18 °C above the food intake, reached the highest peak at 25 °C, the water temperature dropped below 13 °C, the food intake decreased significantly, down to about 9 °C when stopping feeding, water temperature exceeds 30 °C food intake is also obvious reduce. According to some experiments, with small fish as bait, the food intake of blue crab at 25°C is 17%-20% of body weight. Therefore, before the feeding, check the foraging situation of the blue crab for the previous feeding and increase or decrease the amount of food as appropriate. Too little feed on the bait will affect the growth and development of the crab. If you put too much, you will waste the bait, and it will cause water quality to deteriorate.
To sum up, bait should be made according to different conditions such as seasons, weather changes, and tides. Generally during April-August, the climatic conditions are good, and crabs consume the most food. In addition, after changing the water during the tidal period, the amount of food consumed by the crab is greater, and the amount of feeding should be increased by a factor of two; in case of excessive rainfall, the water in the pool is turbid, and crabs are not allowed to feed, and the amount of feeding can be appropriately reduced; when the weather is hot, crabs are The appetite will also weaken; when the weather is cold and the water temperature drops below 9°C, you can stop feeding.
Third, feeding method According to the habit of eating crabs, they should be divided into two feedings every day, and they should be fed once every 5 o'clock in the morning. The amount should be about 40% of the daily feeding amount; When it is released once, the amount of feed is about 60%.
The bait should be placed around the pool, not in the center of the pool, and should be even, so as to avoid crabs fighting for food and causing injury due to clamps. It is also convenient to check the food condition of the bait and the cleaning of the bait. Some foods are processed before they can be placed. If fish and shrimp are used as bait, they must not be deodorised, so as not to affect the quality of water and crab health. The big fish should be chopped and put in. The thick shelled snails or bivalves should be shelled before they are released. The thin shell of the shellfish, such as red meat blue peony, short-toothed bream, duckbill cricket, top bream, Chinese green The oysters can be placed in shelled living bodies so as to avoid incomplete impact on the water quality.
Management measures The management work during feeding is very important and relates to the production and quality of blue crabs. Therefore, special personnel must be responsible and strict management in order to receive good results. Management work mainly includes the following measures.
First, to maintain proper water quality and good water quality The quality of water quality is good or bad, directly affect the life and growth of green crab. If the amount of water is insufficient, the oxygen content is low and the water temperature changes greatly, which is unfavorable to the growth of crabs. In order for the crab to grow well, it is necessary to maintain a sufficient amount of water and good water quality, so it is necessary to constantly change the water and control the water level. 1, change the water: generally change the water every 2-3 days once, if the weather is not good, can be extended properly, but not more than 7 days, so as not to deteriorate the quality of water, affecting the growth of crab, resulting in illness and death. It is not necessary to change the water every day. This will make it difficult for water to be clarified and hinder the feeding of crabs. Change the water according to the tide, but do not choose to do when the sun is too strong at midday, so as not to cause too large a temperature difference between the old and the new water, it is best to do it sooner or later. Also control the amount of water, not too fierce, so as not to increase the water turbidity. When changing the water, pay attention to the salinity. The difference between the freshly injected seawater and the original crab pool should not be too different. Do not drain when draining, and maintain a water level of 20 cm. Otherwise, the mud will drown the crab after entering the water. If the time is longer, the crab will suffocate. Change the water once after the rain to prevent the water quality from deteriorating. 2. Control water level: According to the living habits of blue crab, its water depth requirements are different in different seasons. In winter, the depth of water is generally maintained at about 30 cm at low tide and about 1 m at high tide. When the cold wave comes, the water level should be raised. When the heat is hot, the water level increases to 1.5-2 meters. If the stocking density is high, the water level must be raised accordingly. It is best to put some scallops in the crab pond, which can shave and improve the water quality. It can also be used as bait.
2. Regularly inspect crabs during May-September for frequent activity and easy escape, especially when the weather is hot. Therefore, always check the pool embankment, bamboo (or bamboo fence), mesh, in particular, whether the gate has a gap and loopholes, each harvest once will be a comprehensive repair of the dyke.
Third, observe the crab feeding conditions and remove the residual bait to observe whether the amount of feed and crab growth, and the development of the ovary, and timely removal of residual bait, so as not to make the water worse, affect the growth of crabs. The method of clearing the residual bait is that it is usually carried out during the drainage process, stirring with a six-tooth rake or a hoe at the place where the bait is stored, and the shells are picked up, so that the muddy water and the residual bait flow out of the pool with the water.
Fourth, pay attention to weather changes in the weather, the threat to the blue crab is very large, especially the heavy rain, will make the pool water salinity mutation, and sometimes cause the entire pool crabs are dead. Therefore, we must pay attention to the changes in the weather, it is best to contact the local meteorological department, prepare in advance, control the water level to ensure the normal life of the crab.
Fifth, disease prevention Due to the climate, such as sudden rain, it will cause changes in the salinity of the sea, so that the physiological functions of crab osmotic pressure can not adapt to sudden changes, resulting in some diseases. This happens at all stages of crab's ovarian development. The symptom is that the ovarian tissue of the female crab is rotted, and it also causes the footsteps to be similar to the color of the ovaries. The Cantonese people often call white awns called white awns, and it is called yellow awns in pinkish yellow. After the foot base has a color, the base section is broken off and the color of the base mucous is the same as the color observed on the surface. If the water in the pool is too light, the edema at the base of the foot and the tummy site will occur.
After the diseased crab is found, it is necessary to keep the diseased crabs separately to avoid infection and adjust the proportion of pool water in time. In addition, the crab slaves and barnacles parasitic in the abdomen of the crab should be promptly removed.
Harvested green crabs can be bred to maximum gestation after 20-40 days of feeding (referring to more than 150 grams of crab) under adequate feed and good management. If mating female crabs, the ovaries are already full of the breastplate. On the front edge, some are filled with eggs at the base of the back of the head, chest, intestine, and abdomen. According to the experience of the masses, it is considered that harvesting is appropriate when there are thick matches in the front edge of the head breastplate. If the ovary matures too much, the crabs will easily die, making it difficult to store and transport the crabs.
First, the harvest method The harvest of the blue crab is in the form of a round of rotation, that is, put the seedlings while harvesting. There are many methods for harvesting, which can be divided into two types. One is to use the habit of gathering crabs near the gate at high tide and trying to escape. The second is to put dry water for harvest after the ebb tide. 1, crab net capture method: In the warm season, when the tide rises, the blue crab often swim against the tide to the gate, commonly known as playing with water. According to the living habits of blue crabs, crab nets can be used for fishing at gate gates. The crab net consists of a wooden frame and a mesh sheet. It is square and has a handle. The size of the net depends on the size of the gate. This fishing method works well. 2. Crab trapping method: Crab cages are made of bamboo rafts and are rectangular. The height and width are basically the same as the height and width of gates. When the tide rises, the crab cages are placed on the gates, and then the gates are opened and the water is released. Crab ponds and crabs will flow back into the cage. After the crab cages are filled with crabs or flat tide, the crab cages can be lifted and the gates must be closed before the cages are raised. 3, dry tide pool harvest method: This harvest method is mostly used for large harvest. At the time of ebb tide, when the water is drained and the water is drained almost dry, the man catches the pool. The tools used are six-tooth rakes and an elliptical fishing net. When starting from the side of the crab pool, the six-toothed oyster crab will slowly move and when the crab is encountered, the crab will be picked up, caught in the fishing net, poured into the bucket, and continue to stir. This method is also effective, but when caught, it is easy to be injured by crabs. Take special care.
Second, the sale of the sale of the blue crab will be put into the barrel, put some green leaves, can prevent the crabs from each other, the best time to tie up the crab, into the bamboo basket. For long-distance transportation, crabs should be soaked into the sea for several minutes every day in the summer to keep them from dying for 3-4 days. In the winter, the bamboo baskets should be covered with bags and straw to prevent the crabs from freezing and the crabs should be frozen. In order to prevent the cold wind from blowing directly into the mouth, the crabs will die. In this winter shipment, the blue crabs should be sprayed with some seawater every day after leaving the water, so that they can survive for 6-7 days, but the crabs cannot be directly immersed in water.
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