Fish defense cold damage practical technology
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July 11 11:09:09, 2025
1. **Fishing Pond Selection**. Choose sheltered, sunny winter ponds that are deeper than 2 meters for natural overwintering. The water in the overwintering pond should not remain stagnant for long periods. It is recommended to exchange part of the water every 20 to 30 days, replacing about 1/4 to 1/5 of the total volume to prevent water pollution and maintain good water quality.
2. **Wind Barrier and Cold Hole Prevention**. Construct a 2-meter-high windbreak using straw or mud on the northern side of the pond. Round the east-west slopes of the eastern and western sides to reduce the impact of cold winds. This helps maintain stable water temperatures during cold spells. A drainage ditch should be built around the pond to prevent stagnant water from entering and lowering the temperature. Additionally, dig a 40 cm deep shelter from the bottom of the pond, extending 2 meters in depth and 0.8 meters in diameter. This shelter can be constructed with bricks or buried ceramic tubes, providing fish with a safe place to hide during extreme cold.
3. **Plastic Film Greenhouse Construction**. After setting up the wind barrier, build an insulated greenhouse over the fishing pond using plastic film. Use bamboo or wood to create a "person"-shaped roof along the edge of the pond, with a height of about 2.5 meters above the ground. Cover the structure with two layers of plastic film and seal it tightly, using mud to reinforce the edges. Tilapia overwintering ponds typically cover an area between 40 to 100 square meters, with a water depth of more than 2 meters. Both cement and earthen ponds can be used. Stocking density depends on water temperature, quality, and volume. Generally, 15 brood fish per cubic meter or 25 tails, and 300 fish under 10 cm in size, can be stocked. In better conditions, up to 30–40 broodstock per cubic meter and 400–500 fish can be placed. Flowing pools may use higher stocking rates. Maintain dissolved oxygen levels at around 2 mg/L. Without insulation, outdoor overwintering can result in mortality rates as high as 70%–80%. It's best to move fish indoors or cover outdoor ponds with plastic greenhouses. Stocking density in greenhouses is approximately 100 fish per square meter. With proper management, survival rates can reach 80%–90%. During cold nights or rainy days, thick grass curtains can be used to keep the greenhouse warm. On sunny days, open the cover to allow solar heating. If the temperature becomes too high, ventilate and replace some water. For sudden drops in temperature, warming methods such as steam heating or infrared lamps can be used. Steam heating involves placing a stove near the pond, boiling water in a pot, and directing steam through a bamboo tube into the pool. Infrared lamps (250W) can be installed 30 cm above the water surface, spaced 60 cm apart, with absorbent material placed below to prevent condensation. Turn off the lamps when the water reaches 20°C. Infrared heating offers fast warming, low energy use, and has antibacterial properties that help prevent disease in tilapia.
4. **Regular and Balanced Feeding**. Even though fish metabolism slows down in winter, they still require energy to survive. Feeding remains essential to prevent frost damage and maintain health. The goal is not to increase weight but to ensure survival. High-quality feed with balanced nutrition is crucial. Avoid excessive protein; instead, focus on amino acid balance, vitamins, and minerals. Winter feed for tilapia can have around 20% protein but higher energy content, using ingredients like glutinous rice, bran, bean cake, and malt. Fresh greens like leaves can also be included. Before and after wintering, supplement with energy, protein, fats, and vitamins, especially B-complex, A, D, E, and choline. Calcium and phosphorus are important for yolk development and cold resistance. Proper feeding improves stress resistance and reduces disease risk.
5. **Water Temperature Management**. If the water temperature drops suddenly, immediate action is needed—either by replacing water or using warming methods. Cold waves often bring continuous low temperatures and rain, leading to poor water quality and increased risk of diseases like anchor worm infestations. Besides water changes and aeration, microbial treatments should be applied regularly. Insecticides must be used promptly to control pests and prevent their spread.