River crab farming in greenhouses has become a popular investment project in the coastal areas of East Jiangsu and East China due to its low investment, easy start-up, minimal risk, and high profitability. Based on extensive field research and practical experience, the author has developed several improved techniques for greenhouse-based river crab cultivation. The following are key strategies aimed at enhancing breeding efficiency and sustainability.
1. **Improvement of Infrastructure Technology**
The scientific design of infrastructure is crucial for stable and high-yield seedling production. However, current greenhouse nurseries face several challenges.
1.1 **Pool Size Optimization**
Most nursery pools currently have an area ranging from 40 to 50 m², with some reaching up to 80 m². While larger pools help maintain stable water quality initially, they pose problems later. Water exchange becomes difficult, and waste accumulation leads to poor water conditions. This increases the risk of disease, especially during the Z5 to M stages. To address this, the author recommends reducing pool size to between 20 and 30 m² for better control and management.
1.2 **Bottom Treatment**
Traditional soil bottoms can absorb contaminants but lack the ability to break them down. Over time, the soil becomes saturated, leading to poor water quality. The author suggests covering the bottom with color stripe film, which not only helps collect waste more effectively but also promotes biofilm formation and stabilizes pH levels.
1.3 **Gas Stone Placement**
In traditional setups, gas stones are placed 20 cm above the bottom, creating an oxygen-depleted zone below. This can lead to harmful gas buildup and negatively impact larvae. By placing gas stones directly on the color stripe film, oxygen distribution improves, and the density should be around 2-3 units per square meter.
2. **Enhancements in Nursery Management**
2.1 **Water Treatment**
Bleaching powder is commonly used to disinfect water, but it can produce harmful byproducts under high temperatures. Instead, the author recommends using polymerized aluminum salts to clarify the water, followed by methylene blue to oxidize nitrites and Buddha powder to adsorb ammonia and hydrogen sulfide. A 300-mesh sieve filter is also advised.
2.2 **Temperature Control**
Maintaining a consistent temperature of 21°C during the early stages (Z1–Z2) and gradually increasing it to 24°C as the crabs develop helps improve growth rates. Delaying the start of the season to late April allows for better temperature conditions and healthier larvae.
2.3 **Feeding Practices**
Although commercial feed is cost-effective, it can be less palatable and prone to contamination. Feeding every two hours with small portions and ensuring proper digestion through feeding mother support helps reduce stress and improve survival rates. Adjustments should be made based on larval stage and density.
2.4 **Water Quality Management**
Regular water changes, dirt removal, and the use of photosynthetic bacteria are essential for maintaining good water quality. The best time for water changes is at 3 am, and the author suggests suctioning dirt once per stage for Z1–Z3 and daily for Z4–Z5. Immobilizing photosynthetic bacteria with PVA enhances their effectiveness in improving sediment conditions.
2.5 **Lighting Adjustments**
Using colored films and fluorescent lights helps provide adequate illumination, promoting algae growth and reducing oxygen debt and ammonium levels, especially after midnight.
2.6 **Disease Prevention**
Viral infections, such as those caused by zebra virus, are often overlooked. Acyclovir baths and bait treatments have proven effective in controlling these diseases, offering a targeted approach to prevent large-scale losses.
By implementing these improvements, farmers can significantly enhance the efficiency, productivity, and sustainability of river crab breeding in greenhouse environments.
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