Key measures to prevent cold damage in fish ponds in winter

In the cold winter with low temperatures, fish ponds often suffer from excessively thick ice on the water surface, causing fish to freeze to death, starve to death or suffocate. Doing a good job of preventing cold damage in winter so that fish can safely overwinter lays a good foundation for robust winter growth of fish, stocking in early spring and early marketing, and greatly improves fish farming efficiency. Years of practice have proven that there are mainly the following measures for preventing cold damage to fish:

1. Deep water prevents cold damage. Choosing a pond that is sheltered from the wind and facing the sun with a water depth of more than 2 m can allow fish to overwinter safely. At the same time, the water in the overwintering pond must not remain static for a long time. Usually, part of the pond water is replaced every 20 to 30 days, each time replacing 1/4 to 1/5 of the total pond water, to prevent pond water pollution. Where conditions permit, natural environmental conditions such as hot spring water and deep underground well water can also be used for overwintering.

2. Walls and holes prevent cold damage. Cold damage is prevented by setting up wind-blocking walls and cold-shelter holes. The specific method is to build a windbreak barrier more than 2 m high with straw or earth on the north side of the fish pond, and build earth walls sloping toward the south on the east and west sides to form a dustpan shape, so as to reduce attacks from the north wind. Drainage ditches should be built around the pond to prevent accumulated water outside the pond from flowing into the pond and lowering the pond water temperature. In the north windbreak wall, 1 to 2 cold-shelter holes 2 m deep and 0.8 m in diameter can be dug at 40 cm from the pond bottom. The hole walls can be built with bricks or buried ceramic pipes. When a cold wave hits, fish can hide in the cold-shelter holes to escape the cold. Practice has proven that this method of preventing cold is low in cost and obvious in effect.

3. Greenhouses prevent cold damage. On the basis of setting up windbreak walls and cold-prevention holes, building plastic film cold-prevention greenhouses has an even better effect. The method is to build a “”-shaped roof over the pond along the pond edge with bamboo or wood, with a distance of about 2.5 m from the ground to the roof, cover it with two layers of plastic film, and connect it with the pond edge to form a sealed cover. The film can be sealed around with earth. The area of the overwintering pond is generally 40 to 100 sq m, with a water depth of more than 2 m. Cement ponds and earthen ponds are both acceptable. Stocking density can be determined according to water temperature, water quality and water volume. Generally, 15 to 25 brood fish can be stocked per cubic meter of water, or 300 fingerlings below 10 cm; for ponds with better conditions, 30 to 40 brood fish can be stocked per cubic meter of water, or 400 to 500 fingerlings; for flowing-water ponds, the high-density stocking rate for flowing-water aquaculture can be used as a reference, and it is appropriate to maintain dissolved oxygen in the pond water at 2 mg/L. At night or on cloudy and rainy days, thick straw curtains and other coverings can be used to keep the temperature inside the greenhouse, while on sunny days the straw curtains and other coverings should be lifted to use solar energy for heating. When the water temperature is too high, ventilation should be carried out and some new water added.

4. Heating prevents cold damage. ① Steam heating: set up a stove beside the overwintering pond, boil water in an iron pot, and let steam pass from a specially made bamboo tube on the pot lid through a connected rubber hose into the overwintering pond to raise the pond water temperature. ② Infrared lamp heating: in an overwintering pond covered with a plastic film greenhouse, install one 250-watt infrared bulb for every 35 sq m of water surface, 30 cm from the water surface, and fix a piece of water-absorbing thick cardboard or other water-absorbing material about 60 cm above the bulb to prevent water droplets condensed on the film from water vapor falling onto the bulb and causing it to burst or start a fire. Turn off the lamp when the water temperature rises to 20°C. Infrared lamps have high heat, fast heating, low electricity use and simple installation, and also have the effect of sterilizing and preventing diseases such as saprolegniasis in fish.

5. Adding feed prevents cold damage. During the overwintering period, feeding bait must not be neglected, especially the feeding of high-protein concentrate. Increasing the feeding of concentrate with high protein content can improve cold resistance and prevent the physical condition of overwintering fish from declining. When preparing it, attention should be paid to nutritional balance, especially the balance of amino acids and sufficient vitamins and trace elements. Generally, the protein content of feed for fish during the overwintering period should be about 25%, while the protein content of feed for tilapia can be lower at about 20%, but the energy content should be relatively high. It can mainly consist of fine rice bran, wheat bran, soybean cake and malt, and should often be fed together with some duckweed and fresh tender vegetable leaves. For soft-shelled turtles, the main approach is to strengthen cultivation to improve their own resistance. Soft-shelled turtles need supplemental nutrition before and after overwintering, and first of all, energy and protein supplementation should be strengthened. The fat content can be raised to 3% to 5%, and as much fresh live feed as possible should be fed, with targeted supplementation of vitamins and calcium, phosphorus, etc. Insufficient sunlight in winter easily leads to calcium deficiency, and more phosphorus is needed to increase yolk deposition. During the overwintering period, soft-shelled turtles require larger amounts of most B vitamins, vitamin A, vitamin D, vitamin E and choline than during the normal rearing period, so these substances should be appropriately increased. For all fish, feeding concentrate must also follow the “three fixeds&rdquo, namely fixed quality, fixed time and fixed quantity.

6. Increasing oxygen prevents cold damage. If the river surface freezes too thickly and the water body under the ice lacks oxygen, fish can suffocate and die. At this time, snow should be swept away and ice broken immediately, water should be replaced in time, oxygen-increasing machinery should be started, and microbial preparations should be applied regularly to improve water quality. In particular, silver carp and bighead carp in some “old water” ponds are also prone to diseases such as anchor worm disease under oxygen-deficient conditions, so while increasing oxygen, insecticide should also be applied in time for effective control, so as to achieve simultaneous prevention and treatment of cold damage and disease.