Detailed Explanation of Key Points for Ecological Farming Techniques of Chinese Mitten Crab
Ecological Farming Techniques for Chinese Mitten Crab
The Chinese mitten crab, also known as the river crab, is a premium aquatic product of our county. It is delicious, highly nutritious, a high-grade aquatic product much loved by consumers, and one of the main freshwater aquaculture species for earning foreign exchange through export. Along the Langchuan River basin, our county has abundant ponds, lake shoals and reservoir resources, with lush aquatic plants, fresh water quality, and rich varieties of snails, clams and benthic organisms, making it suitable for developing river crab farming. At present, our county has more than 50,000 mu under river crab farming, with an annual output of more than 2,000 tons, accounting for one-tenth of the county's total aquatic product output.
This technique is designed to achieve a river crab yield of 50-60 kg per mu, an average size of more than 3 liang, and a recapture rate of more than 70%.
I. Pond Conditions
Newly dug ponds (excavated by bulldozer) are best, though ordinary ponds are also acceptable. Specific requirements: area of 10-30 mu, with a minimum of no less than 5 mu and a maximum of no more than 50 mu; water depth of 1.2-2 m, averaging about 1.5 m; slope ratio of 1:3-4, ensuring a certain shallow shoal area (gentle slopes make it harder for river crabs to burrow); silt depth below 10 cm, preferably around 5 cm; pond corners rounded in an arc shape; a shallow shoal area in the center of the pond (flat bottom substrate), with a maximum water level of 0.5-0.8 m; a deep-water zone left around the center of the pond outside the front and back of the shoal ridge, 5-8 m wide, with a maximum water level reaching 1.5-2 m; water inlet and outlet set on the diagonal of the pond to facilitate the formation of circulating water flow when filling; convenient water inlet and drainage, with good water quality in the external river. Depending on specific circumstances, a supporting water storage, disinfection and purification pond may be provided (planted with aquatic plants and an appropriate amount of water hyacinth), with a water capacity suitable for adding 20 cm of water level to the crab pond at one time.
II. Pond Clearing and Disinfection
Pond clearing and disinfection are generally required to be completed before the Spring Festival. First, remove excess silt (for old crab ponds, it is best to use a bulldozer to improve the quality), and after dredging, expose to the sun for 15-30 days to promote the decomposition of organic matter in the bottom mud. Then fill with 20 cm of water, and sprinkle quicklime at 150-200 kg per mu over the entire pond, immediately followed by evenly turning and raking the bottom mud; tea seed cake may also be used in combination to remove wild fish. Before use, soak the tea seed cake for 24 hours and add 1% salt water for a better effect, with a sprinkling concentration of 20-30 g per cubic meter.
III. Preparation Before Stocking
1. Anti-escape facilities On the inner side around the pond ridge, enclose with thickened film, calcium-plastic board, or aluminum sheet, buried 10-15 cm into the mud and rising 50 cm above the ridge surface, with a post for support every 0.5-1 m; it is best to also set up netting around the outer perimeter, 2 m high.
2. Filtration facilities Use 60-mesh double-layer screen mesh to filter water inlet and drainage.
3. Temporary holding area 10 days before the crab juveniles are stocked, enclose 1/10-1/5 of the pond area with netting as a temporary holding area, located in the deep-water zone or at the crab harvesting ditch (a relatively deeper water area). When aquatic plant coverage reaches 50%-60%, remove the netting of the temporary holding area. The temporary holding period generally lasts until April, and no later than the end of May, so as not to affect river crab growth.
4. Selecting crab juveniles It is advisable to purchase crab juveniles locally from nearby sources. Requirements are basically uniform size, intact legs and claws (including no wear on the claw tips), glossy color, fresh with no attachments, and semi-transparent long-legged Yangtze River water system crab juveniles, 100-200 individuals per kg.
5. Treatment before stocking First soak in pond water for 2 minutes, then lift out briefly, then soak for another 2 minutes and lift out, repeating 3 times. Then bathe in 10-20 mg/L potassium permanganate for about 30 minutes, or wash in a 3-4% salt water solution for 3-5 minutes, and then stock in the temporary holding area at the pond. When stocking crab juveniles, the water level should be controlled at 50-60 cm (in spring).
This technique is designed to achieve a river crab yield of 50-60 kg per mu, an average size of more than 3 liang, and a recapture rate of more than 70%.
I. Pond Conditions
Newly dug ponds (excavated by bulldozer) are best, though ordinary ponds are also acceptable. Specific requirements: area of 10-30 mu, with a minimum of no less than 5 mu and a maximum of no more than 50 mu; water depth of 1.2-2 m, averaging about 1.5 m; slope ratio of 1:3-4, ensuring a certain shallow shoal area (gentle slopes make it harder for river crabs to burrow); silt depth below 10 cm, preferably around 5 cm; pond corners rounded in an arc shape; a shallow shoal area in the center of the pond (flat bottom substrate), with a maximum water level of 0.5-0.8 m; a deep-water zone left around the center of the pond outside the front and back of the shoal ridge, 5-8 m wide, with a maximum water level reaching 1.5-2 m; water inlet and outlet set on the diagonal of the pond to facilitate the formation of circulating water flow when filling; convenient water inlet and drainage, with good water quality in the external river. Depending on specific circumstances, a supporting water storage, disinfection and purification pond may be provided (planted with aquatic plants and an appropriate amount of water hyacinth), with a water capacity suitable for adding 20 cm of water level to the crab pond at one time.
II. Pond Clearing and Disinfection
Pond clearing and disinfection are generally required to be completed before the Spring Festival. First, remove excess silt (for old crab ponds, it is best to use a bulldozer to improve the quality), and after dredging, expose to the sun for 15-30 days to promote the decomposition of organic matter in the bottom mud. Then fill with 20 cm of water, and sprinkle quicklime at 150-200 kg per mu over the entire pond, immediately followed by evenly turning and raking the bottom mud; tea seed cake may also be used in combination to remove wild fish. Before use, soak the tea seed cake for 24 hours and add 1% salt water for a better effect, with a sprinkling concentration of 20-30 g per cubic meter.
III. Preparation Before Stocking
1. Anti-escape facilities On the inner side around the pond ridge, enclose with thickened film, calcium-plastic board, or aluminum sheet, buried 10-15 cm into the mud and rising 50 cm above the ridge surface, with a post for support every 0.5-1 m; it is best to also set up netting around the outer perimeter, 2 m high.
2. Filtration facilities Use 60-mesh double-layer screen mesh to filter water inlet and drainage.
3. Temporary holding area 10 days before the crab juveniles are stocked, enclose 1/10-1/5 of the pond area with netting as a temporary holding area, located in the deep-water zone or at the crab harvesting ditch (a relatively deeper water area). When aquatic plant coverage reaches 50%-60%, remove the netting of the temporary holding area. The temporary holding period generally lasts until April, and no later than the end of May, so as not to affect river crab growth.
4. Selecting crab juveniles It is advisable to purchase crab juveniles locally from nearby sources. Requirements are basically uniform size, intact legs and claws (including no wear on the claw tips), glossy color, fresh with no attachments, and semi-transparent long-legged Yangtze River water system crab juveniles, 100-200 individuals per kg.
5. Treatment before stocking First soak in pond water for 2 minutes, then lift out briefly, then soak for another 2 minutes and lift out, repeating 3 times. Then bathe in 10-20 mg/L potassium permanganate for about 30 minutes, or wash in a 3-4% salt water solution for 3-5 minutes, and then stock in the temporary holding area at the pond. When stocking crab juveniles, the water level should be controlled at 50-60 cm (in spring).