Overwintering fish ponds
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In winter, when various fish species and those that haven't met the market size standards are kept together in the same pond, the oxygen demand of the fish increases due to higher fish density. At the same time, the water surface may freeze, creating a closed environment. If supplemental oxygen is not provided promptly, it can lead to fish suffocation and even mass mortality, causing significant economic losses. Even if fish survive anoxia during winter, their growth in the following season can be severely affected, leading to reduced yields.
To ensure sufficient oxygen levels in overwintering fish ponds, several effective methods can be employed:
1. **Recirculating Water for Oxygenation**
By connecting multiple nearby fish ponds using cement or plastic pipes, water from one pond can be pumped into another. This creates a circulation system where water flows between ponds, increasing its contact with air and allowing more oxygen to dissolve into the water.
2. **Applying Organic Fertilizer**
Adding 150–200 kg of organic fertilizer per acre helps promote the growth of phytoplankton. These microorganisms increase the pond’s photosynthetic activity and water temperature, which in turn boosts dissolved oxygen levels.
3. **Water Exchange with Fertile Water**
Ponds with richer water, often containing more phytoplankton, can be used to refill overwintering ponds. This improves the oxygen content by enhancing photosynthesis and overall water quality.
4. **Stirring the Pond Water**
During severe cold, breaking the ice on the pond surface and stirring the bottom water helps mix the layers. This transfers dissolved oxygen from the upper layer to the lower part, improving oxygen distribution throughout the pond.
5. **Regular Water Changes**
Choose warm, windless days to change a third of the pond water at a time. Ensure the new water temperature doesn’t exceed 3°C. Regular water changes help restore dissolved oxygen and nutrient balance, reduce ice formation, and maintain healthier conditions for the fish.
These practices not only prevent fish deaths but also support better growth and productivity in the next season. Proper oxygen management is essential for successful overwintering and long-term aquaculture success.