Technical key points and precautions for stocking fish fingerlings in winter

1. "Five conversions" of fish ponds. Convert "small ponds" to "large ponds", "stagnant ponds" to "live-water ponds", "shallow ponds" to "deep ponds", "leaking ponds" to "water-retaining ponds", and "emergency ponds" to "flood-control ponds". When renovating ponds, first drain the pond water, and after sun-drying, remove excess sludge from the pond bottom, keeping only a 15-20 cm layer. Remove weeds, dredge channels, and raise the pond embankments.

2. Pond clearing and disinfection. Keep the pond at a water depth of 10 cm. First, for every 667 sq m of water surface, use 90 kg of quicklime or 4 kg of bleaching powder containing 30% chlorine, mix into a paste, and splash it evenly over the whole pond; then fill the pond with water, and for every 667 sq m of water surface use another 12 kg of bleaching powder, spread evenly. Generally, fish can only be stocked after 7 days.

3. Fertilizing the water before stocking. Apply base fertilizer 5-7 days after pond clearing. Generally, for every 667 sq m of pond water surface, apply 500-700 kg of fermented pig manure, or 200 kg of human excrement (new ponds or lean ponds can be given more, while fertile ponds can be given less or none), then fill with water to cultivate plankton and provide natural food for the fish fingerlings.

4. Fingerling specifications. The fingerlings require grass carp, silver carp, and bighead carp with a body length of 15 cm, common carp 13 cm, and crucian carp and bream 10 cm or more. They should also be uniform in size, robust in constitution, with intact scales, undamaged fin rays, thick and short caudal peduncles, thick back muscles, bright coloration, strong upstream-swimming ability, free of disease and injury, and frequently jumping.

5. Stock early without delay. The period from the Winter Solstice to around the Spring Festival, or when the water temperature is 8-10°C, is the best time to stock @#@233@#@ fingerlings. At this time the water quality is stable, the fish body is firm, and the fish are less likely to be injured during catching and transport, with low mortality and disease rates; at the same time, the fingerlings quickly benefit from reduced density, adapt to the environment earlier, begin feeding earlier, and gain weight quickly. Stocking should preferably be done at noon on a sunny day. Frosty days and rainy days when the temperature is too low are not suitable for stocking, to prevent freezing injury to the fish. Before stocking, the fingerlings must be disinfected, generally soaked in 3%-5% salt water for 5-10 minutes to kill pathogenic bacteria on the fish surface.

6. Rational polyculture. Determine a reasonable stocking density and stocking amount according to the water quality, food supply, fingerling size, and other conditions of the fish-rearing water body. For relatively fertile fish ponds, the polyculture ratio is: silver carp 55%-60%, bighead carp 15%, grass carp 10%, common carp 10%, crucian carp, blunt snout bream, bream, etc. 5%-10%; for relatively lean fish ponds, the polyculture ratio is: grass carp 40%-50%, silver carp 20%, bighead carp 5%-10%, common carp 10%, crucian carp, bream, blunt snout bream, etc. 5%-10%. The stocking amount per 667 sq m of water surface is about 1000 fish.

7. Strengthen management. Ponds must have a dedicated person responsible for management, with water changed once every 20 days, first draining and then filling, adding water to a depth of 1.5-20 cm each time. During sudden cold spells, deepen the water level to more than 2 m; during snow accumulation and freezing, remove snow and break ice holes to increase oxygen in the water; for ponds that have not been replenished with water for a long time and have low oxygen content, for every 667 sq m of water surface use 5-6 kg of ammonium nitrate and 3-4 kg of superphosphate, mix them in a cloth bag, and sink it underwater. At noon on sunny days, use a bamboo pole to stir the pond bottom, once a month. Overwintering ponds should be appropriately supplied with pig manure, distillers' grains, soybean cake, or rapeseed cake, etc., to raise the water temperature and meet the small feeding needs of overwintering fingerlings. When the water temperature reaches 7-8°C in early spring, bait and fertilizer should be applied early to cultivate fertile water and promote rapid fish growth.