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Utilizing the Nursery Workshop Dongcun Sansui Swimming Crab Technology
The Tripitaka crab, a rare and highly prized edible crab found along China's coastal regions, is cherished for its exquisite flavor and rich nutritional value. Having live crabs on the New Year’s table is not only a symbol of prosperity but also a long-standing aspiration among many. To achieve off-season marketing and enhance the profitability of this valuable species, we successfully implemented a winter seawater nursery technique from 2001 to 2002. This method allowed the Dongchu Tripitaka crabs to be cultivated and sold during non-traditional seasons, increasing their market value by up to 1.5 to 3 times. Below are the key technical measures that were applied during this process.
**1. Preparations Before Winter Storage**
**1.1 Workshop and Pool Renovation**
We utilized idle and nursery workshops that were easy to drain and covered with black plastic sheeting to maintain warmth and block light. The winter storage pools had a bottom area of 20–40 square meters and a depth of 120–150 cm. Each pool was equipped with 6–10 air stones placed evenly at the bottom for oxygenation. Pools were thoroughly cleaned and sterilized before use. A layer of fine sand (10–12 cm) was laid at the bottom, washed and soaked in a 10 ppm potassium permanganate solution for 25–30 minutes. The sand covered 3/5 to 4/5 of the pool, leaving a 1/5 to 2/5 gap near the outlet for bait placement and water exchange. Water was filtered and filled to a depth of 50 cm the day before introducing the crabs.
**1.2 Selection of Winter Crabs**
Crab stocking was timed based on weather and production conditions, typically between mid-October and early December when outdoor temperatures ranged from 8°C to 13°C. Crabs were sourced either from fishing boats or selected from local stocks. Only healthy female crabs with strong vitality, intact appendages, and no injuries were chosen. They were carefully tied to prevent damage from mutual clamping and transported to indoor holding pools with a water depth of 40–50 cm. After 4–8 hours of acclimation, they were bathed in a 300 ppm formaldehyde solution for 20–30 minutes, rinsed, and then transferred to the winter storage pools at a density of 8–12 crabs per square meter.
**2. Daily Management During Winter Storage**
**2.1 Feeding**
Crabs were fed once daily in the evening with high-quality live bait such as sandworms and small fish. The feeding amount varied between 1% and 6% of the crabs’ body weight, depending on water temperature. Bait was washed and disinfected before being placed in designated areas, not directly on the sand.
**2.2 Water Changes**
Water levels were maintained at 100–120 cm. When water temperatures were above 8°C, water was changed every 3 days, replacing 70–80% of the total volume. For lower temperatures, changes occurred every 5 days, replacing 50–60%. Residual bait and dead crabs were removed during each change, and temperature differences were kept within 0.5°C.
**2.3 Temperature Control**
Winter storage water temperature was maintained between 5°C and 12°C. Insulation methods like straw curtains and controlled heating were used to manage temperature fluctuations. Ventilation was adjusted based on temperature to ensure stability.
**2.4 Disinfection**
When water temperatures exceeded 8°C, disinfection with 100 ppm formaldehyde was done weekly. For lower temperatures, it was performed every 10–15 days. Disinfection was combined with routine water changes.
**2.5 Additional Care**
During rainy or low-pressure weather, intermittent aeration was used to prevent hypoxia. Crabs were observed daily for activity and mortality, and water temperature was recorded twice a day. Detailed records were kept to monitor performance.
**3. Discharge Timing**
Discharge was scheduled based on market demand, usually around the Spring Festival when prices were higher. If water temperatures rose above 13°C, crabs were discharged within 15 days to avoid egg development.
**4. Winter Storage Test Results**
In 2001 and 2002, a 480 m² nursery was used for winter storage trials. In 2001, two batches were released in February and March, achieving an overall survival rate of 86.7%. In 2002, survival rates improved significantly, reaching 93.23%.
**5. Discussion**
The use of underutilized nursery facilities not only increased facility efficiency but also enabled off-season sales, boosting profit margins. After two years, crabs sold post-storage fetched 1.75 and 1.2 times the winter price, respectively. The technology proved practical and scalable.
The trial results showed an average weight gain of 4.08% in 2001 and 5.45% in 2002. Although survival rates were lower in the first year due to insufficient insulation, improvements in management led to better outcomes. With proper care, survival rates could reach over 95%, and weight gains could exceed 7%.
Comparisons between sea crabs and pond crabs showed no significant difference in survival rates under similar conditions. Therefore, sub-pool storage was not necessary. The optimal stocking density was found to be no more than 15 crabs per square meter, with no need for continuous aeration.
Male crabs were also tested in 2001, but their survival rates were poor, possibly due to physiological factors that require further study. Overall, the project demonstrated great potential for sustainable and profitable crab farming in China.