As the old saying goes, "In winter, the fish is only three minutes long." However, practical experience has shown that the period from the winter solstice to the beginning of spring is actually the ideal time for introducing fish species. During this time, fish are strong, their scales are tight, and they have a high level of adaptability. Combined with lower water temperatures, which reduce fish activity, this makes the process of catching and stocking fish much more efficient and increases survival rates. Additionally, managing fish during the winter helps avoid many issues related to overwintering, making it easier for them to grow early in the spring.
But how can we improve the survival rate of fish during the winter? Here are some key strategies:
1. **Prepare the Fish Pond Properly**
If the pond is in poor condition, it needs to be renovated. Small, shallow, or dead pools should be transformed into larger, deeper, and more functional ponds that support fish growth during winter. Even if the pond is in good shape, regular maintenance is essential. This includes draining the water, exposing the bottom to sunlight or freezing, removing excess silt (keeping only 15–20 cm), clearing weeds, and reinforcing the pond walls.
2. **Clean and Fertilize the Pond**
Common disinfectants used for cleaning include quicklime and bleaching powder. Quicklime is most effective as it not only kills harmful bacteria but also increases calcium levels in the water. Disinfection should be done on a sunny day. Drain the pond so the water level is about 5–10 cm, then apply 120–150 kg of lime per mu, spread it evenly, and mix thoroughly. After 5–7 days, when the chemicals have evaporated, refill the pond with water. Apply 150–200 kg of decomposed human manure per acre as base fertilizer to enrich the water and promote natural food sources.
3. **Choose Healthy Fish Species**
Winter fish should be selected from healthy, uniform-sized individuals with full scales, intact fins, thick bodies, bright coloration, and active movement. Fish should be at least 12 cm long. Before stocking, they should be soaked in a 2%–3% salt solution or a 3%–5% bleach solution for 15 minutes to eliminate surface pathogens. Fish farms with better facilities can also use an inactivated vaccine against hemorrhagic disease. For fish over 18 cm, inject 0.5 ml per fish; for smaller ones, 0.3 ml per fish.
4. **Stock Smartly**
Based on the water quality, depth, and available feed, choose the right mix of fish species and stocking density. For grass-fed areas, raise more herbivorous fish like carp. In well-fertilized ponds, raise more silver carp. For bottom feeders, add eels or loaches. The recommended ratios are: for fertilized ponds, 20%–30% omnivores and 70%–80% herbivores; for general waters, 25%–45% omnivores and 55%–75% herbivores; for flowing water or large ponds, 60%–80% herbivores and 20%–40% omnivores. The ratio between mid and bottom layers should be 55%–65% and 35%–45%, respectively.
5. **Strengthen Management**
During winter and early spring, low temperatures require focused management. Focus on the "four preventions": preventing ice formation in shallow areas, avoiding water pollution from feeding, stopping ice buildup and oxygen depletion that could suffocate fish, and controlling plankton blooms that may cause flooding. Preventing frost damage is especially crucial. When the temperature drops to 1°C, fish become paralyzed, and below -3°C, species like grass carp, mud carp, and shrimp can freeze to death. To protect them, deepen the water or use plastic greenhouses and other insulation methods to keep the pond warm.
