Key Technical Measures for Stocking Fish Fry in Winter

As the saying goes, "Stock fish fry in spring and they catch disease; stock fish fry in winter and they grow three fen." Practice has proven that the period from the Winter Solstice to the Start of Spring is the best time to stock fish fry. There are three reasons: first, the fry are plump and firm-scaled at this time, with strong adaptability. Second, the low water temperature weakens the fish's activity, resulting in a high survival rate during catching and stocking. Third, it avoids the trouble of merging ponds for overwintering, allowing the fry to be dispersed and intensively reared earlier, promoting early spring growth.

1. Pond renovation.

Use the idle winter season to renovate fish ponds: turn small ponds into large ones, stagnant ponds into aerated ones, and shallow ponds into deep ones. Ponds in relatively good condition should also be repaired: drain the pond water, expose the bottom to sunlight or freezing, dig out excess silt, remove weeds, and raise and reinforce the embankments.

2. Pond clearing and disinfection.

Commonly used disinfectants include quicklime, tea seed cake, and bleaching powder. Quicklime gives the best disinfection effect; it not only increases the calcium content of the pond water but also acts as a direct fertilizer. Disinfection must be carried out on a sunny day. For dry disinfection, use 50-80 kg of quicklime per mu, leaving 5-10 cm of standing water in the pond; if the water depth is 1 m, use 120-150 kg of quicklime.

3. Fertilizing the water.

Five days after pond disinfection, fill the pond with clean water and apply 150-200 kg of decomposed human and livestock manure per mu to fertilize the water and cultivate natural food organisms in the water.

4. Fry selection.

Select fry of the same age, uniform size, robust constitution, intact scales, undamaged fins, thick back muscle, bright coloration, lively swimming behavior, and a body length of over 12 cm for stocking.

5. Strict disinfection.

Fry must be disinfected before entering the pond. Generally, a 3%-5% salt solution can be used to soak the fry for 20-30 minutes. Where conditions permit, black carp and grass carp fry over 18 cm can each be injected with 0.5 ml of diluted inactivated vaccine against black carp and grass carp hemorrhagic disease; those under 18 cm should each be injected with 0.3 ml.

6. Species combination.

Determine the stocking species and quantity based on the water quality, water depth, food availability, and management level of @#@233@#@ water area. Where there is plenty of grass, stock more grass carp and bream; fertilized ponds are suitable for silver carp and bighead carp; where there is abundant bottom food, stock more crucian carp and common carp. The ratio of feeding fish to silver carp and bighead carp: in fertilized ponds 30%-20% to 70%-80%; in ordinary waters 25%-45% to 75%-55%; in flowing-water ponds or those with convenient irrigation and drainage and sufficient water supply, 60%-80% to 40%-20%. The ratio of mid-water to bottom-water fish is 55%-65% to 45%-35%.

7. Rearing management.

In winter and spring, when temperatures are low, in addition to routine management requirements, attention should be paid to the "four preventions": first, prevent the pond water from being too shallow; second, prevent feeding too frequently; third, prevent ice formation and oxygen depletion; fourth, prevent the water from becoming too fertile.

(1) Prevent frostbite. When the pond water temperature drops to 1°C, fish activity decreases; below -3°C, grass carp, silver carp, and bighead carp will freeze to death. Prevention methods: (1) Do a good job of cold protection and insulation, and deepen the pond water; (2) When temperatures are high, appropriately feed some soybean cake, rapeseed cake, etc., to enhance the fish's cold resistance.

(2) Prevent and treat saprolegniasis. This disease is prevalent in late winter and early spring. Diseased fish swim abnormally and lose appetite, eventually becoming emaciated and dying. Prevention and treatment methods: (1) Do not injure the fish during catching, transport, and stocking; (2) Apply 0.15 g of malachite green per cubic meter of water over the entire pond; (3) Apply 2 g of Chinese gallnut per cubic meter of water over the entire pond; (4) Soak the fish in a 50 g/L salt solution for 5 minutes.