From March 2002 to November 2004, I stationed a large-scale crab breeding experiment in the ecological environment of Dong Tai Lake in Xinlian Village, Yokohama Town, and achieved good economic and ecological benefits. We are now testing the situation in 2004. Summarized as follows.
First, materials and methods
1. The choice of net fence area The water in the fence area is fresh and pollution-free. The perennial water level is 1.2 to 1.8 meters. It has a certain amount of micro-flowing water. The bottom of the lake is flat and the bottom is hard. The bottom mud is about 10 cm, and the pH value is 7.8 to 8.3. Concentration above 12.53 mg/l, dissolved oxygen above 4.5 mg/l. The surrounding area of ​​the net is full of aquatic grasses and abundant benthos resources. The water environment is very suitable for the growth of river crabs.
2. The net surrounding structure and setting test are surrounded by a net with an area of ​​90 mu. The net surrounding structure is composed of a polyethylene mesh, a rope, a bamboo pile, a gabion and a cage net, and has a single-layer structure. The total height of the net perimeter is 2.7 to 3.8 meters, which is 1.5 to 2.0 meters above the water surface; the mesh is 2.4 centimeters, and the coefficient of condensation is 0.65; the net mesh is connected to the gabion below the stone and sinks to the bottom of the lake by more than 20 centimeters. At the upper end of each bamboo pile; bamboo piles with a diameter of about 8 cm of bamboo, erected fixed wall network, higher than the normal water level of 1.5 meters above, spacing 2 to 3 meters; mesh around the upper end of a set of 40 to 50 cm wide cornices A 45-degree angle to the wall network; a cage net placed around the perimeter.
3. Rotating animal husbandry In order to protect the ecological environment of the East Taihu Lake, a rotational grazing system is adopted in the net enclosure area, that is, 1/2 of the surface area of ​​the culture area is used to raise crabs on the net and 1/2 of the water is recuperated. . In the net-encircling area, artificial cultivation, artificial transplantation and natural restoration of high-quality aquatic plants such as Vallisneria alternifolia, Hymenocallis circulans and Elodea are carried out. At the same time, algae and other benthic organisms are transplanted to accelerate the restoration and regeneration of resources and restore the ecological environment of lake water bodies. .
4. Elimination of predatory fish Black-fish, squid, and grass carp are the most harmful fish on the nets. These fish not only replenish benthic animals and quality aquatic plants with crabs, but also swallow crab species and soften them. Shell crab. Therefore, before the stocking of crabs, conduct a thorough clean-up by using several large-power electric fishers alongside each other to remove the enemy fishes in the nets several times.
5. Improve the type of aquatic weeds and control the density of aquatic weeds in the growth nets of aquatic weeds should be maintained at more than 90%. In case of scarcity of aquatic weeds, weeds such as Elodea, Hydrilla verticillata, and Malay-eyed Oyster should be transplanted without water pollution. In addition, according to the growth of aquatic plants within the enclosure, the upper parts of the aquatic plants are cut off from time to time so that they can grow tender grass in time for the crabs to eat.
6. Put on snails after releasing sufficient amount of snail nets to remove predator organisms. The best time for snail feeding is before Ching Ming. The amount of snail feeding is 250-300 kg/mu, allowing it to reproduce naturally. When the resources of snails in the network enclosure are insufficient, they must be added in time to ensure that there are enough snail resources in the network enclosure.
7. Select high-quality crab species for stocking and breeding in the Yangtze River water quality Chinese mitten crabs, to ensure the quality of crab species. The size of the crabs to be put is larger, and the number of mussels is 50 to 60/kg. The number of local self-cultivated crabs is 300. Each crab species has been selected to eliminate precocious crab species. The stocking time of crab species is from 2 to 3 months.
8. The holding management of crab species is to increase the survival rate of crab species and protect the aquatic resources in the enclosure. A small net enclosure is enclosed in the enclosure, and the area is about 1/5 of the grid perimeter. Raised in a small net enclosure. When the water temperature reached 15°C or more, the feeding amount was gradually increased, and the bait was mainly wild fish. The daily feeding amount was 7% to 10% of the total weight of the crab in the net enclosure. Remove small nets before the first clam shelling.
9. The scientific feeding arrangement for feeding the whole year is 25% to 30% of the total feeding amount in the first half of the year and 70% to 75% of the total feeding amount in the second half of the year. The daily feed is 5% to 8% of the total body weight of the crab body in the net enclosure, and it is adjusted in time according to the weather, water temperature, water quality, and the growth of the river crab. Feed twice a day, 7 to 8 o'clock in the morning and 2/5 of the total daily dose, and 3/5 in the evening. Feeding species are wild fish, snails, corn and aquatic grasses.
10. Day-to-day management Crab species will continue to patrol three times a day in the morning, evening and evening after stocking, observing the water quality and the growth of the crab's feeding activities, checking the surrounding facilities, and promptly taking measures to identify problems. Especially during the flood season and the typhoon season, it is necessary to reinforce the surrounding facilities and prevent crabs from escaping.
11. Proper fishing time from the end of September to mid-to-late November should be appropriate for catching crabs.
Second, the test results
1. Harvest
From the end of September to mid-November 2004, a total of 4171.5 kilograms of commercial crabs were obtained, with an average yield of 46.35 kilograms, an average size of 194.5 grams per bag, and a rate of 79.3%. Among them: the average size of male crabs is 210 grams/ton, and the average size of female crabs is 180 grams/ton. During the entire cultivation period, a total of 10,532 kilograms of commercial feed was fed, and the feed coefficient was 2.83.
2. Economic benefits Due to the large size and high quality of commercial crabs, the average selling price of commodity crabs is as high as 127 yuan/kg, and the total income is 531,390 yuan. Expenditure is 36,000 yuan for the net facilities, 32,400 yuan for the crab species, 42820 yuan for the feed, 36,500 yuan for the planting of aquatic plants, 45,000 yuan for the snails, 72,000 yuan for the surface water, 36,000 yuan for the labor costs, and a total expenditure of 300,720 yuan. The net income is 230,670 yuan, and the net income per mu is 2,563 yuan. The input-output ratio is 1:1.77.
Third, summary and discussion
1. The experimental results show that large-scale crabs with large size, high quality, good efficiency, and high rate of catching are the advantages of the large-scale crabs in the eco-culture of net enclosures. Integrated optimization and innovation can meet the growing demand for quality and large-scale river crabs in domestic and foreign markets, significantly increase the economic benefits of net enclosures, and promote the sustained, rapid and healthy development of lake fisheries, which has great promotion value.
2. This experiment has strengthened measures such as rational planting and management of aquatic weeds, reasonable deployment and proliferation of live snails, promoted the improvement of ecological environment within net enclosures, implemented ecological farming, and created a good environment for healthy growth of river crabs. Without using any medicine, the produced crabs are all pollution-free green foods. Therefore, large-scale crabs in the eco-culture of nets can raise the quality and safety of crabs and enhance the market competitiveness of crabs.
3. The stocking density of the experimental crabs was 300 birds per mu. The average catching rate was 194.5 grams per bird, and the average catching rate was 79.3%. The stocking density of the surrounding cages was 450 birds per mu. The average catching rate was 166.7 grams per bird, and the average catch rate was 54.6%. The ecological density of the crabs in the net enclosure is low, but the efficiency of the specifications, the rate of recovery, and the area per unit of the crabs is significantly better than that of the general caged crabs. The reason may be that the ecological enclosure of crabs created a suitable ecological environment for the growth of crabs. In addition, the large-scale, high-quality species of crabs that have been selected for breeding are used. The stocking densities are small, the living space is large, and the feeding is scientific and reasonable. Crab growth, while reducing the crabs because of high density, small activity space and opportunity to kill each other, so the rate of high recovery.
4. Adopting rotational grazing techniques, according to ecological principles, the biodiversity of the nets and moorings in the nets can be restored and reconstructed in time to achieve the purpose of purifying the water quality, so that the overall impact of the net culturing of Lake Tai Lake on the eutrophication of lake water is obvious. Reduce the negative growth of aquaculture pollution and comprehensively improve the lake's ecological environment.
Author: Jiangsu Wuzhong District Aquatic Animal Husbandry Bureau
First, materials and methods
1. The choice of net fence area The water in the fence area is fresh and pollution-free. The perennial water level is 1.2 to 1.8 meters. It has a certain amount of micro-flowing water. The bottom of the lake is flat and the bottom is hard. The bottom mud is about 10 cm, and the pH value is 7.8 to 8.3. Concentration above 12.53 mg/l, dissolved oxygen above 4.5 mg/l. The surrounding area of ​​the net is full of aquatic grasses and abundant benthos resources. The water environment is very suitable for the growth of river crabs.
2. The net surrounding structure and setting test are surrounded by a net with an area of ​​90 mu. The net surrounding structure is composed of a polyethylene mesh, a rope, a bamboo pile, a gabion and a cage net, and has a single-layer structure. The total height of the net perimeter is 2.7 to 3.8 meters, which is 1.5 to 2.0 meters above the water surface; the mesh is 2.4 centimeters, and the coefficient of condensation is 0.65; the net mesh is connected to the gabion below the stone and sinks to the bottom of the lake by more than 20 centimeters. At the upper end of each bamboo pile; bamboo piles with a diameter of about 8 cm of bamboo, erected fixed wall network, higher than the normal water level of 1.5 meters above, spacing 2 to 3 meters; mesh around the upper end of a set of 40 to 50 cm wide cornices A 45-degree angle to the wall network; a cage net placed around the perimeter.
3. Rotating animal husbandry In order to protect the ecological environment of the East Taihu Lake, a rotational grazing system is adopted in the net enclosure area, that is, 1/2 of the surface area of ​​the culture area is used to raise crabs on the net and 1/2 of the water is recuperated. . In the net-encircling area, artificial cultivation, artificial transplantation and natural restoration of high-quality aquatic plants such as Vallisneria alternifolia, Hymenocallis circulans and Elodea are carried out. At the same time, algae and other benthic organisms are transplanted to accelerate the restoration and regeneration of resources and restore the ecological environment of lake water bodies. .
4. Elimination of predatory fish Black-fish, squid, and grass carp are the most harmful fish on the nets. These fish not only replenish benthic animals and quality aquatic plants with crabs, but also swallow crab species and soften them. Shell crab. Therefore, before the stocking of crabs, conduct a thorough clean-up by using several large-power electric fishers alongside each other to remove the enemy fishes in the nets several times.
5. Improve the type of aquatic weeds and control the density of aquatic weeds in the growth nets of aquatic weeds should be maintained at more than 90%. In case of scarcity of aquatic weeds, weeds such as Elodea, Hydrilla verticillata, and Malay-eyed Oyster should be transplanted without water pollution. In addition, according to the growth of aquatic plants within the enclosure, the upper parts of the aquatic plants are cut off from time to time so that they can grow tender grass in time for the crabs to eat.
6. Put on snails after releasing sufficient amount of snail nets to remove predator organisms. The best time for snail feeding is before Ching Ming. The amount of snail feeding is 250-300 kg/mu, allowing it to reproduce naturally. When the resources of snails in the network enclosure are insufficient, they must be added in time to ensure that there are enough snail resources in the network enclosure.
7. Select high-quality crab species for stocking and breeding in the Yangtze River water quality Chinese mitten crabs, to ensure the quality of crab species. The size of the crabs to be put is larger, and the number of mussels is 50 to 60/kg. The number of local self-cultivated crabs is 300. Each crab species has been selected to eliminate precocious crab species. The stocking time of crab species is from 2 to 3 months.
8. The holding management of crab species is to increase the survival rate of crab species and protect the aquatic resources in the enclosure. A small net enclosure is enclosed in the enclosure, and the area is about 1/5 of the grid perimeter. Raised in a small net enclosure. When the water temperature reached 15°C or more, the feeding amount was gradually increased, and the bait was mainly wild fish. The daily feeding amount was 7% to 10% of the total weight of the crab in the net enclosure. Remove small nets before the first clam shelling.
9. The scientific feeding arrangement for feeding the whole year is 25% to 30% of the total feeding amount in the first half of the year and 70% to 75% of the total feeding amount in the second half of the year. The daily feed is 5% to 8% of the total body weight of the crab body in the net enclosure, and it is adjusted in time according to the weather, water temperature, water quality, and the growth of the river crab. Feed twice a day, 7 to 8 o'clock in the morning and 2/5 of the total daily dose, and 3/5 in the evening. Feeding species are wild fish, snails, corn and aquatic grasses.
10. Day-to-day management Crab species will continue to patrol three times a day in the morning, evening and evening after stocking, observing the water quality and the growth of the crab's feeding activities, checking the surrounding facilities, and promptly taking measures to identify problems. Especially during the flood season and the typhoon season, it is necessary to reinforce the surrounding facilities and prevent crabs from escaping.
11. Proper fishing time from the end of September to mid-to-late November should be appropriate for catching crabs.
Second, the test results
1. Harvest
From the end of September to mid-November 2004, a total of 4171.5 kilograms of commercial crabs were obtained, with an average yield of 46.35 kilograms, an average size of 194.5 grams per bag, and a rate of 79.3%. Among them: the average size of male crabs is 210 grams/ton, and the average size of female crabs is 180 grams/ton. During the entire cultivation period, a total of 10,532 kilograms of commercial feed was fed, and the feed coefficient was 2.83.
2. Economic benefits Due to the large size and high quality of commercial crabs, the average selling price of commodity crabs is as high as 127 yuan/kg, and the total income is 531,390 yuan. Expenditure is 36,000 yuan for the net facilities, 32,400 yuan for the crab species, 42820 yuan for the feed, 36,500 yuan for the planting of aquatic plants, 45,000 yuan for the snails, 72,000 yuan for the surface water, 36,000 yuan for the labor costs, and a total expenditure of 300,720 yuan. The net income is 230,670 yuan, and the net income per mu is 2,563 yuan. The input-output ratio is 1:1.77.
Third, summary and discussion
1. The experimental results show that large-scale crabs with large size, high quality, good efficiency, and high rate of catching are the advantages of the large-scale crabs in the eco-culture of net enclosures. Integrated optimization and innovation can meet the growing demand for quality and large-scale river crabs in domestic and foreign markets, significantly increase the economic benefits of net enclosures, and promote the sustained, rapid and healthy development of lake fisheries, which has great promotion value.
2. This experiment has strengthened measures such as rational planting and management of aquatic weeds, reasonable deployment and proliferation of live snails, promoted the improvement of ecological environment within net enclosures, implemented ecological farming, and created a good environment for healthy growth of river crabs. Without using any medicine, the produced crabs are all pollution-free green foods. Therefore, large-scale crabs in the eco-culture of nets can raise the quality and safety of crabs and enhance the market competitiveness of crabs.
3. The stocking density of the experimental crabs was 300 birds per mu. The average catching rate was 194.5 grams per bird, and the average catching rate was 79.3%. The stocking density of the surrounding cages was 450 birds per mu. The average catching rate was 166.7 grams per bird, and the average catch rate was 54.6%. The ecological density of the crabs in the net enclosure is low, but the efficiency of the specifications, the rate of recovery, and the area per unit of the crabs is significantly better than that of the general caged crabs. The reason may be that the ecological enclosure of crabs created a suitable ecological environment for the growth of crabs. In addition, the large-scale, high-quality species of crabs that have been selected for breeding are used. The stocking densities are small, the living space is large, and the feeding is scientific and reasonable. Crab growth, while reducing the crabs because of high density, small activity space and opportunity to kill each other, so the rate of high recovery.
4. Adopting rotational grazing techniques, according to ecological principles, the biodiversity of the nets and moorings in the nets can be restored and reconstructed in time to achieve the purpose of purifying the water quality, so that the overall impact of the net culturing of Lake Tai Lake on the eutrophication of lake water is obvious. Reduce the negative growth of aquaculture pollution and comprehensively improve the lake's ecological environment.
Author: Jiangsu Wuzhong District Aquatic Animal Husbandry Bureau
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