Crabs are widely distributed in China, especially in lakes and rivers in the middle and lower reaches of the Yangtze River. Wujiang City, Jiangsu Province began to develop Taihu Lake around the end of the 1980s to raise crabs. After more than a decade of development, a set of practical techniques has been developed to meet the needs of large lakes.
First, the choice of water area requires that the bottom of the lake is flat, with micro-flow, submerged plants flourishing, abundant benthos, fresh water, abundant dissolved oxygen, pH above 7.0, and normal water level between 80cm and 150cm.
Second, the construction of network facilities
1. The net perimeter of the net perimeter is preferably 20 mu - 30 mu. The net enclosure adopts a double-layer net structure, the outer layer is a protection net, the inner layer is a culture zone, and the two-layer net spacing is 5.0m, and a “cage net†is set up between them to check the situation of escape crabs and to prevent escape. At the top of the inner net, a “T†inverted mesh or a plastic film with a width of 20cm–40cm is used to prevent escape. The bottom of both layers is connected to a gabion and buried in the bottom of the lake. The net perimeter is fixed on the outside with bamboo piles, the spacing of bamboo piles is about 1.5m, and the height of the net enclosure is 2.5m--3.0m.
2. In the first year of the construction of new net enclosures in temporary holding areas, there is no need to set up a holding area for crabs. However, before the stocking of crabs is started in the second year, it must be raised to ensure the catch rate and specifications of the rearing crabs. The holding area is a single-network structure with inverted nets and a lower stone cage buried in the bottom of the lake for escape prevention. The holding area accounts for about 30% of the net area.
Third, seed stocking
1. Before stocking for pre-reservation crabs, various methods such as cages and screens are used to eliminate wild fish in the enclosures. At the same time, hidden objects must be set up in the holding area to increase habitats for crabs and clams. Improve the survival rate of crab breeding.
2. The species of crabs for raising crabs is preferably crab species cultivated in the river system of the Yangtze River. The size of crab species is 100/kg--200/kg, and the stocking quantity is controlled at about 350/mu. The stocking time should be around mid-March. .
Stocking should be selected when the weather is warm and sunny and the water temperature is high. When stocking, the crabs should be soaked in formaldehyde, crab, and other liquids for about 1 minute, removed for 5 minutes, and then soaked in water for 2 minutes, then removed for 10 minutes, and repeated 2 times - 3 times. When the crab species absorb water, they are put into the holding area to increase the survival rate.
3. The good water environment and abundant palatable natural foods in the crab breeding nets are the key to the success or failure of ecological breeding crabs. Therefore, the transplantation and cultivation of aquatic weeds and benthic animals must be done in the remaining 70% of the surface of the crabs. Until a certain group size is formed. Generally, the crab species can be placed in the net enclosure from the holding area from late June to early July. One way is to use a cage net to catch the crab species from the holding area and count it into the net enclosure. Basically mastering the survival rate after the demobilization and demolition of the holding area; the other method is to directly remove the holding area without count, and incorporate the holding area into the fence. The advantage is that the operation is simple and fast. The disadvantage is that the fence The number of crab species is difficult to count.
Fourth, feed feeding
1. Feed types The feed for crabs can be divided into vegetable feeds, animal feeds and compound feeds. Botanical baits include duckweed, water peanuts, bitter herbs, black leaf algae, malaysian seeds and other natural aquatic plants and pumpkins, watermelon rinds, and other vegetable and bean cakes, soybeans, wheat, corn and other food baits. Size, look at plants, crabs, see plants, vividly illustrated the importance of aquatic plants in crab culture. Therefore, we must pay attention to planting and protection of aquatic plants in the early stage of culture, otherwise it will seriously affect the market size of crabs. Animal foods include small fish, shrimp, silkworm cocoons, snails, pig blood, livestock and poultry waste, animal carcasses, etc. It is also possible to put fertilized snails on the net to allow them to grow and reproduce as mid-later crabs. Animal food. The compound feed is a full-priced special feed formulated manually according to the nutritional requirements of different stages of crabs.
2. Feeding volume In general, the first year of netting waters can meet the growth needs of river crabs with only a small amount of feeding, and the second year must have sufficient feed supply to meet the nutritional needs of river crabs. The crab's feeding intensity is related to the season, the water temperature and the different growth stages of crabs. From the end of March to the beginning of April, the water temperature rises, the crabs begin to feed in full, and the April-October is the peak season for crabs to eat, especially in September. The crabs have the highest food intensity. In the first half of the year, 35% to 40% of the total feeding amount is fed into the whole year, and from July to November, 60% to 65% of the total amount is fed. The feeding amount is determined according to the weight of the crabs, and the amount of the total weight of the stored crabs is 10% - 15% in the early stage, 5% - 10% in the total weight of the crabs is added in the later stage, and the crabs eat according to the weather, water temperature, and water quality. The situation is flexible and reasonable adjustments. At the same time, whether the quantity of aquatic weeds in the nets is stable is also an important indicator for judging whether or not the feed amount is reasonable.
3. Feeding method Crab feeding is generally fed twice a day, and the feeding amount accounts for 1/3 and 2/3 of the whole day respectively. Soybeans, corn, wheat, etc. should be cooked before feeding. In the early stage of cultivation, the palatable animal and plant foods should be weighed together to accelerate the recovery of the physical strength of the crab species. In the medium term, the plant-based diet should be used as the main ingredient. In the later stage, more animal feed should be fed to achieve the “two-headed and middle-green†food. .
V. Disease Prevention and Control The net enclosure is carried out in open waters. Once the occurrence of crabs is more difficult to control, therefore, the net enclosure of crabs must adhere to the principle of “prevention firstâ€. The following measures should be taken:
1. Crab species are not purchased from high-risk areas of crabs.
2. Before the crabs are stocked, a medicinal bath is required to kill the body surface pathogens.
3. Every 15 days - 30 days with 15mg/L lime water sprinkled to improve the water environment, so that the pH of the water is alkaline.
4. Every 15 days - 30 days crabs take medicine baits for 5 days to enhance resistance to disease.
5. Ensure the quality of feed, scientifically feed scientifically, improve feed utilization, and reduce the damage to the surrounding water body environment due to the deterioration of the residual bait.
6. For the scientific use of aquatic plants within the enclosure, the coverage of aquatic plants should be maintained at a reasonable level to maintain the ecological balance of the surrounding waters.
Sixth, daily management
1. Adhere to the morning and evening patrols. During the day, the main observations were water temperature and water quality changes. In the evening and night, the activities of crabs and eating and eating were mainly observed so that management measures could be adjusted in time.
2. Regularly check, repair, and reinforce anti-escape facilities. In particular, during the flood season and typhoon season, patrol inspections must be stepped up, and the heightening and reinforcement of the facilities should be done in a timely manner. Problems must be solved in time to prevent crabs from escaping.
3. Strengthen care soft shell crab. During the peak period of crab shelling, it is necessary to provide palatable food, provide a good hidden environment, and guard against enemy invasion.
4. In the listing season of adult crabs, it is necessary to strengthen supervision, strengthen patrols, guard against escape, and prevent theft.
Seven, fishing sales
After 10 months, the crabs gradually reached sexual maturity, which can be used according to market conditions, trapped in cages and sold in due course. If the market is low, the crabs can be raised in crab boxes and sold at the right time.
Zhu Kunquan Wujiang Municipal Fisheries Bureau, Jiangsu Province 215200
First, the choice of water area requires that the bottom of the lake is flat, with micro-flow, submerged plants flourishing, abundant benthos, fresh water, abundant dissolved oxygen, pH above 7.0, and normal water level between 80cm and 150cm.
Second, the construction of network facilities
1. The net perimeter of the net perimeter is preferably 20 mu - 30 mu. The net enclosure adopts a double-layer net structure, the outer layer is a protection net, the inner layer is a culture zone, and the two-layer net spacing is 5.0m, and a “cage net†is set up between them to check the situation of escape crabs and to prevent escape. At the top of the inner net, a “T†inverted mesh or a plastic film with a width of 20cm–40cm is used to prevent escape. The bottom of both layers is connected to a gabion and buried in the bottom of the lake. The net perimeter is fixed on the outside with bamboo piles, the spacing of bamboo piles is about 1.5m, and the height of the net enclosure is 2.5m--3.0m.
2. In the first year of the construction of new net enclosures in temporary holding areas, there is no need to set up a holding area for crabs. However, before the stocking of crabs is started in the second year, it must be raised to ensure the catch rate and specifications of the rearing crabs. The holding area is a single-network structure with inverted nets and a lower stone cage buried in the bottom of the lake for escape prevention. The holding area accounts for about 30% of the net area.
Third, seed stocking
1. Before stocking for pre-reservation crabs, various methods such as cages and screens are used to eliminate wild fish in the enclosures. At the same time, hidden objects must be set up in the holding area to increase habitats for crabs and clams. Improve the survival rate of crab breeding.
2. The species of crabs for raising crabs is preferably crab species cultivated in the river system of the Yangtze River. The size of crab species is 100/kg--200/kg, and the stocking quantity is controlled at about 350/mu. The stocking time should be around mid-March. .
Stocking should be selected when the weather is warm and sunny and the water temperature is high. When stocking, the crabs should be soaked in formaldehyde, crab, and other liquids for about 1 minute, removed for 5 minutes, and then soaked in water for 2 minutes, then removed for 10 minutes, and repeated 2 times - 3 times. When the crab species absorb water, they are put into the holding area to increase the survival rate.
3. The good water environment and abundant palatable natural foods in the crab breeding nets are the key to the success or failure of ecological breeding crabs. Therefore, the transplantation and cultivation of aquatic weeds and benthic animals must be done in the remaining 70% of the surface of the crabs. Until a certain group size is formed. Generally, the crab species can be placed in the net enclosure from the holding area from late June to early July. One way is to use a cage net to catch the crab species from the holding area and count it into the net enclosure. Basically mastering the survival rate after the demobilization and demolition of the holding area; the other method is to directly remove the holding area without count, and incorporate the holding area into the fence. The advantage is that the operation is simple and fast. The disadvantage is that the fence The number of crab species is difficult to count.
Fourth, feed feeding
1. Feed types The feed for crabs can be divided into vegetable feeds, animal feeds and compound feeds. Botanical baits include duckweed, water peanuts, bitter herbs, black leaf algae, malaysian seeds and other natural aquatic plants and pumpkins, watermelon rinds, and other vegetable and bean cakes, soybeans, wheat, corn and other food baits. Size, look at plants, crabs, see plants, vividly illustrated the importance of aquatic plants in crab culture. Therefore, we must pay attention to planting and protection of aquatic plants in the early stage of culture, otherwise it will seriously affect the market size of crabs. Animal foods include small fish, shrimp, silkworm cocoons, snails, pig blood, livestock and poultry waste, animal carcasses, etc. It is also possible to put fertilized snails on the net to allow them to grow and reproduce as mid-later crabs. Animal food. The compound feed is a full-priced special feed formulated manually according to the nutritional requirements of different stages of crabs.
2. Feeding volume In general, the first year of netting waters can meet the growth needs of river crabs with only a small amount of feeding, and the second year must have sufficient feed supply to meet the nutritional needs of river crabs. The crab's feeding intensity is related to the season, the water temperature and the different growth stages of crabs. From the end of March to the beginning of April, the water temperature rises, the crabs begin to feed in full, and the April-October is the peak season for crabs to eat, especially in September. The crabs have the highest food intensity. In the first half of the year, 35% to 40% of the total feeding amount is fed into the whole year, and from July to November, 60% to 65% of the total amount is fed. The feeding amount is determined according to the weight of the crabs, and the amount of the total weight of the stored crabs is 10% - 15% in the early stage, 5% - 10% in the total weight of the crabs is added in the later stage, and the crabs eat according to the weather, water temperature, and water quality. The situation is flexible and reasonable adjustments. At the same time, whether the quantity of aquatic weeds in the nets is stable is also an important indicator for judging whether or not the feed amount is reasonable.
3. Feeding method Crab feeding is generally fed twice a day, and the feeding amount accounts for 1/3 and 2/3 of the whole day respectively. Soybeans, corn, wheat, etc. should be cooked before feeding. In the early stage of cultivation, the palatable animal and plant foods should be weighed together to accelerate the recovery of the physical strength of the crab species. In the medium term, the plant-based diet should be used as the main ingredient. In the later stage, more animal feed should be fed to achieve the “two-headed and middle-green†food. .
V. Disease Prevention and Control The net enclosure is carried out in open waters. Once the occurrence of crabs is more difficult to control, therefore, the net enclosure of crabs must adhere to the principle of “prevention firstâ€. The following measures should be taken:
1. Crab species are not purchased from high-risk areas of crabs.
2. Before the crabs are stocked, a medicinal bath is required to kill the body surface pathogens.
3. Every 15 days - 30 days with 15mg/L lime water sprinkled to improve the water environment, so that the pH of the water is alkaline.
4. Every 15 days - 30 days crabs take medicine baits for 5 days to enhance resistance to disease.
5. Ensure the quality of feed, scientifically feed scientifically, improve feed utilization, and reduce the damage to the surrounding water body environment due to the deterioration of the residual bait.
6. For the scientific use of aquatic plants within the enclosure, the coverage of aquatic plants should be maintained at a reasonable level to maintain the ecological balance of the surrounding waters.
Sixth, daily management
1. Adhere to the morning and evening patrols. During the day, the main observations were water temperature and water quality changes. In the evening and night, the activities of crabs and eating and eating were mainly observed so that management measures could be adjusted in time.
2. Regularly check, repair, and reinforce anti-escape facilities. In particular, during the flood season and typhoon season, patrol inspections must be stepped up, and the heightening and reinforcement of the facilities should be done in a timely manner. Problems must be solved in time to prevent crabs from escaping.
3. Strengthen care soft shell crab. During the peak period of crab shelling, it is necessary to provide palatable food, provide a good hidden environment, and guard against enemy invasion.
4. In the listing season of adult crabs, it is necessary to strengthen supervision, strengthen patrols, guard against escape, and prevent theft.
Seven, fishing sales
After 10 months, the crabs gradually reached sexual maturity, which can be used according to market conditions, trapped in cages and sold in due course. If the market is low, the crabs can be raised in crab boxes and sold at the right time.
Zhu Kunquan Wujiang Municipal Fisheries Bureau, Jiangsu Province 215200
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