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Subsequent investment seedlings develop large-scale river crab technology
Traditional crab farming methods typically involve seeding crabs one at a time, with uniform size specifications. However, in recent years, practical production experiences have shown that using split seedlings on natural water surfaces can yield better economic returns. The test results are summarized as follows:
The experimental area covers 158 acres, located in a natural river gully. It is connected to the external river channel, with stable water flow and an average depth of 2.1 meters, with some areas reaching 3.5 meters deep and shallow zones of about 1 meter. The shallow water area accounts for two-thirds of the total, and the bottom is composed of black loam.
Aquatic plants were planted from August 2004 to May 2005, with 21 tons of algae transplanted. In early April 2005, 203 kg of *Albus* seeds were added. Deep-water zones were planted with goldfish algae, while shallow areas were filled with *Vallisneria*, achieving a coverage rate of 70-80%.
Snail populations were also cultivated, with 36 tons of snails introduced between November 2004 and April 2005, including both native snails and 500 kg of additional snails.
Due to the large scale of the water body and its connection to other areas, traditional dry pond disinfection was not feasible. Instead, nets, gill nets, and osprey techniques were used to remove wild and predatory fish. In November 2004, 14 tons of quicklime were applied, followed by 6 tons of lime water in February 2005 to clean the water before releasing seedlings. Water clarity reached 1.5 meters, with a pH of 7.5–8.5.
For seed stocking, crabs were sourced from the Sheyang Nursery in Jiangsu Province in late May 2004, ensuring they were adapted to local conditions and reducing transportation stress. In August 2004, 50,000 crabs (400–500 eggs/kg) were released, and in July 2005, 31,000 crabs (120–160 eggs/kg) were added, totaling 81,000 crabs over the season, averaging 512 per acre.
Additionally, 100 kg of young shrimp, 2,500 carp, and 1,500 carp seedlings were introduced in December 2004 and May 2005. All seedlings were disinfected with 3–5% saltwater for 10–15 minutes to eliminate surface bacteria and parasites.
Feeding began in mid-March, primarily with chilled fish and some commercial feed. From May to September, sufficient bait ensured good feeding, with about 8% of the crab biomass provided daily. *Vallisneria* served as an indicator of feeding levels—when food was abundant, fewer leaves were eaten, and when it was scarce, more leaves were damaged. Adjustments were made accordingly. Two to three weeks before harvesting, high-protein feed like chilled fish was increased to improve crab quality and market value. A total of 52,000 kg of feed was used throughout the year.
To prevent escape, the focus was on securing the inlet and outlet with double-layered barriers and checking them daily, especially during the rainy season. Crabs were monitored around the clock to reinforce blocking facilities if needed.
Fishing started in late September, peaking in early October, using crab cages.
Economically, 8,714 kg of marketable crabs were harvested, with an average weight of 215 grams and a catch-up rate of 50.03%. Additional catches included 503 kg of carp, 8,493 kg of grass carp, 1,351 kg of green shrimp, and 2,487 kg of other fish. Total output was 955,000 yuan, with crabs contributing 802,000 yuan. Total costs amounted to 3.8135 million yuan, resulting in a profit of 573.65 million yuan, or 3,631 yuan per mu.
Key lessons learned include the need to secure blocking facilities with stakes due to unstable water levels and multiple inlets. Patrols must be intensified during rainy and flood seasons. Timely harvesting is crucial to prevent escapes and improve yield rates.