In 1998, our station undertook the project of “High-yielding and high-efficient production of crabs by net enclosures†issued by the County Bureau of Science and Technology. We have used the shallow water grass lake-Great Lake to carry out comparative experiments on the cultivation of large-size commercial crabs using different specifications and sources of crabs. The success has been achieved. The experimental results are summarized as follows:
1 Materials and Methods
1.1 Test conditions. The experiment was carried out in the large vertical lake in Yandu County, Jiangsu Province. The large vertical lake is a small lake with a water-grass type, with a total area of ​​40,000 mu. The average annual water depth is 1.35 m, the highest historical water level is 369 m, and the lowest water level is 0.31 m. The bottom of the lake is a silty straw residue with organic matter content of 1.74%. The pH is between 7.0 and 8.2, with an average of 7.5. It is medium to slightly alkaline. Dissolved oxygen in water 50cm 8.23mg ~ 12.37mg/L. The total alkalinity was 59.44 mg/L, and the total acidity was 3.56 mg/L. The comprehensive assessment of the water quality was a grade one, which met the standards of drinking water and fishery water quality. Under natural conditions, there are more than 600,000 phytoplankton, such as silicon, green, alpha, blue-green algae, in the lake, and 3,200 zooplankton, such as rotifers, clarifs, and copepods, and reeds, wild rhyolites, Vallisneria, and grasses. , duckweed, water peanuts and other aquatic plants 3kg ~ 5kg/m2; snail 104/m2, weight 216g; gardenia 21/m2, weight 41g. The water flow rate is not fast, the water replacement coefficient is about 1.03, and the water transparency is 30cm to 65cm.
1.2 Test Area Test Set up a net enclosure equipment at a distance of 50m offshore in Hubei Province with a total area of ​​225.5 mu. For the comparative test, the areas designated A, B, and C were divided into 95 acres, 75 acres, and 60 acres, respectively, each with a spacing of 10 meters.
1.3 The net perimeter construction adopts double-layer net enclosures. The two-tier nets are separated by 2m. Bamboo (wood) is used as a fixed pile. The spacing between each pile is 2 to 3m. The cut-out polyethylene webs are sewed and tied with ropes. On the pile, pull the plane up and down and left and right, and the bottom of the net is fixed with a stone cage and ground anchor so that the net foot is tightly adhered to the bottom mud. The gabion is pressed into the bottom mud 20cm, and the upper part of the net is 1m~1.5m above the water surface. On the "T" type mesh, a net made of a plastic film of 30cm to 50cm vertically downward is provided on the upper side of the mesh, and is tightly attached to the mesh.
1.4 Crab species and stocking. The crabs of the A and B species are provided by the seedling base of the County Aquatic Technology Promotion Station. Hyperthyroidism is the next-generation crab of the big eyes of the Yangtze River system. It has a size of 5g to 10g per animal. It will be stocked from January 10 to mid-February. The oysters were young crabs of V grade or above that were cultivated in the early season and were seedlings of 0.5g to 1g/body. They were stocked before April 20th. Profloxacin is purchased from the Liaohe River water system and has a specification of 5g to 10g per animal. It was stocked in early February and ended.
2 Output and Benefits
2.1 Stocking and Harvesting
3 Breeding technology
3.1 Feed the bait. From January to April, the water temperature was lower and the crabs consumed less food. The main use of natural foods was to feed artificial bait starting from May. The feed was 30% for cakes, wheat, freshwater fish, and 70% for snails. . Ten crabs were caught every 10 days, and they were weighed and measured. The internal cages containing the crabs were calculated and the feed was fed as planned (see table). Feed 1 to 2 times a day, mainly in the evening. At the same time keep enough aquatic plants in the network area. Such as water peanuts, barnyardgrass, wormwood, etc., not only for feeding crabs, but also for clams, habitat.
Month feeding conditions Month 1～4 5 6 7 8 9 10
Average water temperature °C 3.5 to 15.2 21.4 24.8 28.4 28.9 24.6 18.9
Daily feeding rate % 5 6 9 9 5 4
Annual feed% 5 10 15 23 23 21 7
3.2 Anti-escape. Adhere to the daily inspections, especially the strong winds, heavy rains, and flood seasons, pay special attention to them, identify problems, and take timely measures to prevent nets and nets from escaping. The protective piles and cages can be added outside the perimeter of the fence to protect the perimeter and monitor the escape of crabs.
3.3 daily management. Frequent removal of weeds and residual bait waste in the netting area, cleaning of the nets, and strengthening of the net enclosure facilities in the flood season will prevent the flooding nets and inverted nets. During the dry season, the submerged dam should be pumped up to maintain a certain aquaculture water level. In the high temperature season every 20 days or so, splashing lime in the net area will not only kill bacteria, but also increase calcium in the water, which will help prevent diseases and make crab shells.
3.4 Fishing. The Liaohe River System crabs stocked by Bing Yang entered sexual maturity in September and began frequent crawling activities. A and B were harvested from mid-October and were harvested at the end of November. The fishing tools were mainly cages and small nets, which could be captured almost one month after continuous capture. Prepare a temporary storage box before harvesting, or use a bamboo (net) sheet in the center of the net fence to fence a small pot for temporary storage of crabs or early release of crab species.
4 Summary and discussion
4.1 Lake water is fresh, pollution-free, water flow is slow, and aquatic grasses, snails, and maggots are rich in resources and are suitable for the growth of river crabs. The crabs raised by the net enclosure “green shell, white belly, and gold claw†are of good quality and meet the export requirements. The use of better water conditions and the cultivation of large-size commodity crabs can improve the market competitiveness of crab breeding and achieve the purpose of improving economic efficiency. It can be seen from the experiment that large-scale crab species of the Yangtze River water system stocked with sea turtles are raised. Due to large specifications and high market prices, the input-output ratio is 1:1.7 and the profit rate is 70% under the condition that the benefit of crabs declines. The crabs cultivated by B and B are small in size and have little profit.
4.2 Large-scale commodity crabs are cultured in lakes and nets, and their critical stocking meets the requirements of the crab species. One is the germplasm of crab species. The crab species in the Yangtze River water system are significantly better than those in the Liaohe River system. The second is the specification of crab species. The specifications are too large, the proportion of precocious crab species is large, the survival rate is low, and the specifications are too small, affecting the growth specifications. It has been proved that the stocking crabs of 5g to 10g per year can be cultivated into large-size crabs weighing only 150g or more. The V young crabs that were stocked for early pregnancy were only about 100g in length.
4.3 In order to solve the crab species problem of large-scale commercial crabs cultured in lakes, we also conducted a trial of early hatching of juvenile crabs, ie, juvenile crabs aged above V in the current year from mid-August to early September, with a specification of about 1,000 eggs per kilogram. The annual crab species was raised. According to the determination, about 1,000 animals were stocked per acre, and the size of the crabs was raised to 50 to 100 eggs per kilogram. There were no precocious individuals and they continued to be raised in the second year. Up to 200g/above, the cost of crab species can be reduced by about 50%.
4.4 Tests have shown that Liaohe river crab species are not suitable for raising in lakes. First, the Liaohe river system is smaller than the lifelong individuals of the Yangtze river system. Second, the last shell of the crabs in the Liaohe river system is about 1 month earlier than that of the Yangtze river system and must be advanced. Capture, otherwise it is difficult to catch, and there is a batch of deaths in the late period of “Green Crabâ€. Third, the survival rate of crabs cultivated with Liao crab as crab species is low, and the general survival rate is only 10 to 30%.
4.5 Young crabs of stage V or above that were cultivated in early-cultivation seedlings in the year were cultured in lakes. Although the growth rate was high and the seed cost was low, the breeding effect was not significant. If a small section of a large net area is used to cultivate crab species and self-breeding and self-cultivation is implemented, the breeding effect can be significantly improved.
1 Materials and Methods
1.1 Test conditions. The experiment was carried out in the large vertical lake in Yandu County, Jiangsu Province. The large vertical lake is a small lake with a water-grass type, with a total area of ​​40,000 mu. The average annual water depth is 1.35 m, the highest historical water level is 369 m, and the lowest water level is 0.31 m. The bottom of the lake is a silty straw residue with organic matter content of 1.74%. The pH is between 7.0 and 8.2, with an average of 7.5. It is medium to slightly alkaline. Dissolved oxygen in water 50cm 8.23mg ~ 12.37mg/L. The total alkalinity was 59.44 mg/L, and the total acidity was 3.56 mg/L. The comprehensive assessment of the water quality was a grade one, which met the standards of drinking water and fishery water quality. Under natural conditions, there are more than 600,000 phytoplankton, such as silicon, green, alpha, blue-green algae, in the lake, and 3,200 zooplankton, such as rotifers, clarifs, and copepods, and reeds, wild rhyolites, Vallisneria, and grasses. , duckweed, water peanuts and other aquatic plants 3kg ~ 5kg/m2; snail 104/m2, weight 216g; gardenia 21/m2, weight 41g. The water flow rate is not fast, the water replacement coefficient is about 1.03, and the water transparency is 30cm to 65cm.
1.2 Test Area Test Set up a net enclosure equipment at a distance of 50m offshore in Hubei Province with a total area of ​​225.5 mu. For the comparative test, the areas designated A, B, and C were divided into 95 acres, 75 acres, and 60 acres, respectively, each with a spacing of 10 meters.
1.3 The net perimeter construction adopts double-layer net enclosures. The two-tier nets are separated by 2m. Bamboo (wood) is used as a fixed pile. The spacing between each pile is 2 to 3m. The cut-out polyethylene webs are sewed and tied with ropes. On the pile, pull the plane up and down and left and right, and the bottom of the net is fixed with a stone cage and ground anchor so that the net foot is tightly adhered to the bottom mud. The gabion is pressed into the bottom mud 20cm, and the upper part of the net is 1m~1.5m above the water surface. On the "T" type mesh, a net made of a plastic film of 30cm to 50cm vertically downward is provided on the upper side of the mesh, and is tightly attached to the mesh.
1.4 Crab species and stocking. The crabs of the A and B species are provided by the seedling base of the County Aquatic Technology Promotion Station. Hyperthyroidism is the next-generation crab of the big eyes of the Yangtze River system. It has a size of 5g to 10g per animal. It will be stocked from January 10 to mid-February. The oysters were young crabs of V grade or above that were cultivated in the early season and were seedlings of 0.5g to 1g/body. They were stocked before April 20th. Profloxacin is purchased from the Liaohe River water system and has a specification of 5g to 10g per animal. It was stocked in early February and ended.
2 Output and Benefits
2.1 Stocking and Harvesting
3 Breeding technology
3.1 Feed the bait. From January to April, the water temperature was lower and the crabs consumed less food. The main use of natural foods was to feed artificial bait starting from May. The feed was 30% for cakes, wheat, freshwater fish, and 70% for snails. . Ten crabs were caught every 10 days, and they were weighed and measured. The internal cages containing the crabs were calculated and the feed was fed as planned (see table). Feed 1 to 2 times a day, mainly in the evening. At the same time keep enough aquatic plants in the network area. Such as water peanuts, barnyardgrass, wormwood, etc., not only for feeding crabs, but also for clams, habitat.
Month feeding conditions Month 1～4 5 6 7 8 9 10
Average water temperature °C 3.5 to 15.2 21.4 24.8 28.4 28.9 24.6 18.9
Daily feeding rate % 5 6 9 9 5 4
Annual feed% 5 10 15 23 23 21 7
3.2 Anti-escape. Adhere to the daily inspections, especially the strong winds, heavy rains, and flood seasons, pay special attention to them, identify problems, and take timely measures to prevent nets and nets from escaping. The protective piles and cages can be added outside the perimeter of the fence to protect the perimeter and monitor the escape of crabs.
3.3 daily management. Frequent removal of weeds and residual bait waste in the netting area, cleaning of the nets, and strengthening of the net enclosure facilities in the flood season will prevent the flooding nets and inverted nets. During the dry season, the submerged dam should be pumped up to maintain a certain aquaculture water level. In the high temperature season every 20 days or so, splashing lime in the net area will not only kill bacteria, but also increase calcium in the water, which will help prevent diseases and make crab shells.
3.4 Fishing. The Liaohe River System crabs stocked by Bing Yang entered sexual maturity in September and began frequent crawling activities. A and B were harvested from mid-October and were harvested at the end of November. The fishing tools were mainly cages and small nets, which could be captured almost one month after continuous capture. Prepare a temporary storage box before harvesting, or use a bamboo (net) sheet in the center of the net fence to fence a small pot for temporary storage of crabs or early release of crab species.
4 Summary and discussion
4.1 Lake water is fresh, pollution-free, water flow is slow, and aquatic grasses, snails, and maggots are rich in resources and are suitable for the growth of river crabs. The crabs raised by the net enclosure “green shell, white belly, and gold claw†are of good quality and meet the export requirements. The use of better water conditions and the cultivation of large-size commodity crabs can improve the market competitiveness of crab breeding and achieve the purpose of improving economic efficiency. It can be seen from the experiment that large-scale crab species of the Yangtze River water system stocked with sea turtles are raised. Due to large specifications and high market prices, the input-output ratio is 1:1.7 and the profit rate is 70% under the condition that the benefit of crabs declines. The crabs cultivated by B and B are small in size and have little profit.
4.2 Large-scale commodity crabs are cultured in lakes and nets, and their critical stocking meets the requirements of the crab species. One is the germplasm of crab species. The crab species in the Yangtze River water system are significantly better than those in the Liaohe River system. The second is the specification of crab species. The specifications are too large, the proportion of precocious crab species is large, the survival rate is low, and the specifications are too small, affecting the growth specifications. It has been proved that the stocking crabs of 5g to 10g per year can be cultivated into large-size crabs weighing only 150g or more. The V young crabs that were stocked for early pregnancy were only about 100g in length.
4.3 In order to solve the crab species problem of large-scale commercial crabs cultured in lakes, we also conducted a trial of early hatching of juvenile crabs, ie, juvenile crabs aged above V in the current year from mid-August to early September, with a specification of about 1,000 eggs per kilogram. The annual crab species was raised. According to the determination, about 1,000 animals were stocked per acre, and the size of the crabs was raised to 50 to 100 eggs per kilogram. There were no precocious individuals and they continued to be raised in the second year. Up to 200g/above, the cost of crab species can be reduced by about 50%.
4.4 Tests have shown that Liaohe river crab species are not suitable for raising in lakes. First, the Liaohe river system is smaller than the lifelong individuals of the Yangtze river system. Second, the last shell of the crabs in the Liaohe river system is about 1 month earlier than that of the Yangtze river system and must be advanced. Capture, otherwise it is difficult to catch, and there is a batch of deaths in the late period of “Green Crabâ€. Third, the survival rate of crabs cultivated with Liao crab as crab species is low, and the general survival rate is only 10 to 30%.
4.5 Young crabs of stage V or above that were cultivated in early-cultivation seedlings in the year were cultured in lakes. Although the growth rate was high and the seed cost was low, the breeding effect was not significant. If a small section of a large net area is used to cultivate crab species and self-breeding and self-cultivation is implemented, the breeding effect can be significantly improved.
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