Key points for overwintering management in the fry and fingerling culture of freshwater pomfret

The freshwater pomfret is a tropical fish species. Its main suitable growth temperature range is between 21-32°C, with the optimum range at 28-30°C. At a water temperature of 16°C, the pomfret only begins to eat a small amount; at 12°C, the fish's balance becomes disturbed; and at 10°C, it causes death. During the overwintering process, water temperatures that are too low will weaken the fish's disease resistance and cause outbreaks, especially in the early overwintering period and during the spring emergence from overwintering. October generally marks the critical period for overwintering fry and fingerling rearing. Therefore, management work before overwintering must be done well:

1. Pond clearing

Ponds used for stocking freshwater pomfret fry and fingerlings for overwintering are generally required to be 2 mu, with a water depth of more than 2 m, to ensure stable water temperature. Before stocking fry, pond clearing must first be carried out to kill harmful organisms in the pond. Generally, 200-250 jin of quicklime per mu should be used for pond clearing, and at the same time 30 ml of Shachongling per mu should be splashed to kill disease-causing organisms. After one week, the fry and fingerlings can be stocked.

2. Feeding

In October-November before overwintering, before the freshwater pomfret fry and fingerlings are placed into the overwintering pond, feeding must be intensified to strengthen their constitution and improve their disease resistance. Generally, high-energy feed such as wheat bran and soybean cake is fed, and daily feeding can be done at 5% of the fish body weight.

3. Stocking density

The density of fry and fingerlings placed into the overwintering pond is generally controlled at about 30,000 tails per mu, to prevent excessive density and easy deterioration of water quality. At the same time, about 500 tilapia fry per mu can be stocked.

4. Fish disease prevention

For freshwater pomfret fry and fingerlings in overwintering ponds, attention must be paid to fish disease prevention, because once disease occurs, treatment is somewhat difficult. Prevention must be strengthened to ensure safe overwintering.

1. When stocking fry and fingerlings in overwintering ponds, operations must be done carefully to avoid injuring the fish. Before entering the overwintering pond, soak them in 3% salt water for 10-15 minutes to kill harmful organisms on the surface of the fry and prevent them from being brought into the overwintering pond.

2. Prevent grass carp from mixing into the overwintering pond, because grass carp is extremely susceptible to infection by the Jiujiang tapeworm parasitic in the intestine. The eggs it releases hatch into coccidian larvae, and its intermediate host is cyclops. When freshwater pomfret fry and fingerlings eat cyclops, it can trigger massive parasitism by the Jiujiang tapeworm in the stomach and intestines, causing death.

3. Use one drug for prevention once a week. Generally, bleaching powder and mercurous nitrate can be used alternately. The methods are:

(1) Hang bleaching powder bags, with 100 g per bag hung near the feeding area for prevention.

(2) Use bleaching powder (containing more than 20% chlorine) at 1 gram per cubic meter, and splash it over the whole pond.

(3) Mercurous nitrate, 0.1 gram per cubic meter of water, splashed over the whole pond.