The purse seine fishing in Lake Yangcheng Lake, located in Bacheng, Kunshan, began in 1987. Initially, the area was just around 1,000 acres. By 2000, it had expanded to 25,000 acres. This article outlines the key techniques used for crab farming in the lake and the construction of purse seines.
First, selecting the right water area is crucial. The lake should have clear, freshwater with slow-moving currents and a depth of about 1.5 meters. The bottom should be hard and flat, free from deep trenches, with soft mud up to 10 cm. The lake must also have abundant natural aquatic resources and a rich supply of benthic organisms.
Next, preparing the fencing materials is essential. The mesh size should be 8 to 9 mesh with 12 threads. Bamboo poles, 20-25 cm in diameter, should be straight and undamaged. The bottom gabion is made of 246 stones, and additional items like Moso bamboo, plastic lines, ropes, and lead wires are also needed.
The fence area is typically between 30 to 50 acres, shaped as a square or rectangle. When setting up the fence, it's best to do so at the end of the year or early January. Choose a flat, trench-free area, and place the piles 1 meter apart. The fence should be high enough to stay above the flood level by 80 to 100 cm. A counter-netting net is placed at the end of the fence, angled inward at 45 degrees, to prevent crabs from escaping. The connection between the net and the bamboo should be slightly loose to avoid damage from wind.
For the gabion setup, the main gabion should have a diameter of 10 to 12 cm, filled to 70–80% to allow proper placement. An auxiliary gabion, 5–6 cm in diameter, is placed inside the main one, 50 cm apart, to prevent crabs from escaping if the main gabion is damaged. After installation, a cage net is set around the four sides of the fence for regular inspections to detect any escape.
In terms of breeding management, crabs are stocked from March to April. Healthy, disease-free crabs weighing 60–80 per kilogram are chosen. Stocking density is usually about 400 crabs per acre. Before releasing them, crabs are soaked in a potassium permanganate solution (10–15 mg/L) for 1–2 minutes until they turn red, which helps disinfect and improve survival rates.
Supplemental feeding starts in early April, with fresh snails added to the nets—300–500 kg per mu—to naturally increase food sources and clean the sediment. Artificial feed is also provided, especially after April when water temperatures rise. Fish, corn, and wheat are given in moderation, while non-polluting drugs are added in June to August to prevent diseases.
Daily management involves checking the nets every day for escapes, inspecting the fence structure every three days, and checking the gabions weekly. Morning and evening checks are done to remove debris, monitor plant growth, and adjust feeding accordingly.
Harvesting begins in late September when crabs reach maturity. Cage nets are used, with large knots placed at 2–3 per mu. Alternatively, anti-escape nets can be used, achieving a recovery rate of about 70%, with an average weight of 150 grams.
In terms of profitability, selling 40 kg of crabs at 210 yuan per kg brings in 8,400 yuan. Costs include 1,000 yuan per mu for the seine net over three years, 330 yuan annually, plus 400 yuan for crabs, 600 yuan for bait, 200 yuan for rent, 800 yuan for labor, and 200 yuan for other expenses, totaling 2,530 yuan. This results in a profit of 5,870 yuan.
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