What are some practical methods for protecting fish and soft-shelled turtles from the cold in winter?

1. Pond selection: Choose a deep-water pond (over 2 m deep) that is sheltered from the wind and faces the sun for natural overwintering. The water in the overwintering pond should not remain stagnant for long periods; usually replace part of the pond water every 20 to 30 days, each time replacing 1/4 to 1/5 of the total pond water, to prevent pond water contamination.

2. Set up windbreaks and cold-shelter holes: On the north side of the pond, a 2 m high windbreak can be built from straw or soil, and on the east and west sides, earthen walls sloping toward the south can be built in a dustpan shape to reduce the impact of the north wind, so that when a cold wave strikes, the water temperature will not drop significantly. Drainage ditches should be built around the pond to prevent accumulated water outside the pond from flowing into it and lowering the pond water temperature. In the north windbreak wall, 40 cm above the pond bottom, 1 to 2 cold-shelter holes 2 m deep and 0.8 m in diameter can be dug; the walls of the holes can be built with bricks or embedded ceramic pipes, so that fish can enter the cold-shelter holes when a cold wave strikes.

3. Build plastic-film cold-protection greenhouses: On the basis of setting up windbreaks, build plastic greenhouses over the pond for insulation. Use bamboo or wood to build a ""-shaped roof along the pond edge, with the distance from the ground to the roof top about 2.5 m, 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 mud. Overwintering ponds for tilapia are generally 40 sq m to 100 sq m in area, with a water depth of more than 2 m; both cement ponds and earthen ponds are 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 fry under 10 cm. For ponds with better conditions, 30 to 40 brood fish or 400 to 500 fry can be stocked per cubic meter of water. 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 the dissolved oxygen in the pond water at 2 mg/L. For juvenile soft-shelled turtles overwintering outdoors, the mortality rate can reach 70% to 80% without insulation measures. Therefore, if conditions permit, juvenile soft-shelled turtles are best moved into indoor ponds for overwintering, or covered with plastic greenhouses in open-air ponds for overwintering, with a stocking density of about 100 per sq m; with good management, the overwintering survival rate can reach 80% to 90%.

When using plastic-film greenhouses for overwintering, thick straw curtains and the like can be used at night or on rainy days to keep the temperature inside the greenhouse; on sunny days, the straw curtains and other coverings should be opened to use solar energy for heating. When the air temperature and water temperature are too high, ventilation should be provided and some new water added. If a cold wave strikes and the water temperature drops, the following heating measures can be taken: (1) Steam heating method: add 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 method: in the above overwintering pond covered with a sealed plastic-film greenhouse, install one 250 W infrared bulb per 35 sq m of water surface, 30 cm above the water surface, and at a distance of about 60 cm above the bulb, fix a piece of thick cardboard or other water-absorbing material that dries easily, to prevent water droplets condensed from water vapor on the film from falling onto the bulb and causing it to burst or start a fire. When the water temperature rises to 20°C, turn off the lamps. Advantages of using infrared heating: infrared lamps give off a lot of heat, heat up quickly, use little electricity, are simple to install, and also have a sterilizing effect, which can prevent fish from developing fungal diseases.

4. Feed concentrated feed on a fixed schedule, in fixed amounts and of fixed quality: Although fish have a lower metabolic level during overwintering, they still need to consume a large amount of energy, so feeding is still an indispensable task during overwintering. The main purpose of overwintering is not to make the fish gain weight, but to prevent the fish from being frostbitten or dying and to keep the fish healthy. To prevent the physical condition of overwintering fish from declining and to enhance the fish's own stress resistance, effort should be put into selecting and formulating feed. When preparing feed, attention should be paid to comprehensive and reasonable nutritional matching; one should not one-sidedly pursue excessively high protein content and excessively fast growth, but should pay more attention to the balance of amino acids and the adequacy of vitamins and trace elements, so as to ensure healthy growth of the fish. For example, the protein content of feed used during the overwintering period for tilapia can be lower, at about 20%, but the energy content should be relatively high; feeding should be based mainly on fine bran, wheat bran, soybean cake and malt, and some duckweed and fresh tender vegetable leaves should often be added. To ensure that soft-shelled turtles overwinter safely, especially by strengthening cultivation to improve their own stress resistance. Soft-shelled turtles need supplemental nutrition before and after overwintering. First, energy and protein supplementation should be strengthened; the fat content can be increased by another 3% to 5%, and as much fresh live feed as possible should be fed, and then vitamin and calcium, phosphorus, etc. should be supplemented in a targeted way. Insufficient sunlight in winter makes calcium deficiency likely, and more phosphorus is needed to increase yolk deposition. During overwintering, soft-shelled turtles require more B vitamins, vitamins A, D and E, and choline than during the normal rearing period, so these substances should be appropriately increased, which helps improve the cold resistance of soft-shelled turtles, enhance their disease resistance, and prevent poor fat metabolism.

5. If the water temperature drops suddenly, heating measures should be taken immediately: The invasion of a cold wave often causes continuous low-temperature rainy weather, which can very easily lead to deterioration of pond water quality and disease in pond fish. In some "old water" ponds, silver carp and bighead carp are prone to anchor worm disease, etc. In addition to paying attention to changing water, frequently turning on aerators, and regularly applying microbial preparations to improve water quality, insecticides and other drugs should also be applied in a timely manner for effective control, so as to prevent the spread and expansion of pests and diseases.