The cultivation of juvenile crabs in plastic greenhouses serves as a fundamental technique for developing various crab farming models. It plays a crucial role in increasing the size of marketable crabs and improving the survival rate of seedlings. This method is based on the biological characteristics of young crabs, creating an optimal ecological environment—such as aquatic plants, suitable water temperature, and adequate food sources—to support their growth. By integrating oyster shells and other natural elements, this system enhances both ecological and economic benefits.
This eco-agricultural model can be implemented on wastelands, including coastal and inland abandoned areas, which not only improves land utilization but also boosts environmental and economic returns. The social impact is equally significant, making it a sustainable and valuable practice for rural development.
Key aspects of the model include:
**1. Greenhouse Construction and Preparation**
- The pool area for scaffolding is typically 0.5 to 1.0 mu (667 square meters), with a depth of 0.8 to 1.2 meters and a water depth of 0.3 to 0.8 meters. The pools are oriented east-west, with a flat bottom and a slope ratio of 1:1.5. Plastic greenhouses are constructed using steel or bamboo frames, with large mesh films fastened and buried into the soil. A central bamboo bridge is installed at 30 cm above the water surface for easy management and feeding.
- Two air pipelines are placed 20 cm from the pool bottom, with air holes drilled every 25 cm. A heating boiler is installed during winter to maintain stable temperatures.
- Before planting, wild and desolate fields should be cleared of thick silt and sun-dried. About 10 days before planting, 250 kg of quicklime per 667 square meters is applied to disinfect the soil.
- Aquatic plants such as water peanuts, bitter grasses, or disinfected willow roots and brown algae are transplanted to provide shelter for juvenile crabs. These plants cover 40% to 60% of the water surface.
- One week before releasing bait, a 60-80 mesh sieve is used to filter the inlet water. Chicken manure (50 kg) and urea (5 kg) are added per 667 square meters to cultivate natural feed.
- Water temperature inside the greenhouse is maintained between 22°C and 28°C. When introducing crabs, the temperature difference between the greenhouse and the nursery should not exceed 3°C.
**2. Seedling Introduction**
- Typically, 5–10 kg of seedlings per 667 square meters are introduced. The crabs should be uniform in size, healthy, and intact. Before placing them in the water, they are sprayed with water 3–4 times or soaked in a bath for 2–3 minutes each time to acclimate.
**3. Production Management**
- Within 15 days of introducing seedlings, the water level is kept at 36 cm and gradually increased to 80 cm. In the mid-to-late stages, water is changed daily by 50%–80%.
- Water quality is managed by maintaining clarity between 40–50 cm. Fertilization, live feed, and cooling are adjusted according to the water conditions.
- Feeding starts one week after seedlings are introduced. Initially, egg yolk, milk powder, and copepods are used, with a feeding rate of 150%–100%. As crabs grow, the diet transitions to fish or fish meal, with feeding rates decreasing accordingly.
- Disease prevention involves applying 5–10 kg of lime per 667 square meters monthly. A mixture of 1% furazolidone or oxytetracycline is combined with bait for 2–3 days. During molting periods, water changes are minimized.
- Daily inspections are conducted, and during hot weather, ventilation is opened from 9 am to 3 pm to ensure proper oxygen levels and timely water changes.
**4. Harvesting Juvenile Crabs**
- After approximately 30 days of culture, crabs reach a size of 2,000–5,000 per kilogram. They can be harvested using methods like drainage collection, net digging, or water picking with nets.
**5. Benefit Analysis**
- The growth rate ranges from 20% to 40%, with 80–120 kg of juvenile crabs produced per 667 square meters. The output value reaches 2.5–4 million yuan, and the profit is between 8,000–15,000 yuan per 667 square meters.
**6. Challenges and Recommendations**
- Seedlings should be placed in shallow water with sufficient vegetation for protection.
- Purchase high-quality seedlings to ensure a high survival rate.
- Maintain fresh aquatic plants, covering at least 30% of the water surface to provide adequate habitat.
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