Overwintering fish ponds
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In winter, when various fish species and those that haven't met market size standards are kept together in the same pond, the oxygen demand of the fish increases due to higher stocking density. At the same time, the water surface may freeze, creating a closed environment. If supplemental oxygen is not managed properly during this period, it can lead to severe oxygen depletion, causing fish to suffocate and die. Even if some fish survive anoxia, they often suffer long-term damage, which can significantly impact their growth in the following season and result in major production losses.
To maintain sufficient oxygen levels in overwintering fish ponds, several effective methods can be applied:
1. **Recirculating Water for Oxygenation** – Connect multiple nearby fish ponds using cement or plastic pipes. Pump water from one pond to another using mechanical systems to create a continuous flow. As the water circulates, it comes into greater contact with the air, allowing more oxygen to dissolve into the water, thereby increasing dissolved oxygen levels.
2. **Applying Organic Fertilizer** – Applying 150–200 kg of organic fertilizer per acre can stimulate the growth of phytoplankton. This boosts the pond’s photosynthetic activity, improves water temperature, and enhances oxygen levels naturally.
3. **Water Exchange with Oxygen-Rich Water** – Introduce well-fertilized water from other ponds into the overwintering ponds. This water contains high levels of phytoplankton, which helps increase dissolved oxygen through enhanced photosynthesis.
4. **Pond Water Aeration by Stirring** – During severe cold, break the ice on the pond surface and stir the bottom water. Mixing the upper and lower layers allows dissolved oxygen from the surface to reach the deeper layers, improving overall oxygen distribution.
5. **Regular Water Changes** – Choose warm, windless days to perform partial water changes. Replace about one-third of the pond water at a time, ensuring the incoming water doesn’t exceed 3°C in temperature. This practice helps restore dissolved oxygen and nutrient balance, reduces ice formation, and maintains healthier conditions for the fish.
By implementing these strategies, fish farmers can effectively manage oxygen levels during the winter months, reducing fish mortality and ensuring better growth outcomes in the next season.