Detailed Explanation of Key Techniques for Autumn Fish Fingerling Rearing

Autumn water temperature generally fluctuates between 20°C and 30°C, making it a good period for fish growth. It is especially the fattening season for smaller, weaker fingerlings, so farmers must effectively strengthen fingerling rearing.

Disinfect and clear the pond. For old fish ponds converted to new ponds for fingerling rearing, after several months of rearing in spring and summer, water quality gradually deteriorates, dissolved oxygen and natural food organisms decrease, and pathogenic microorganisms increase, which can stunt fingerling growth. Grass carp fingerlings in particular are more prone to disease in such old ponds. At this time, fingerlings should be transferred to new ponds for intensive rearing. In areas lacking water sources, seining can be done several times. After all fingerlings are removed, use the original pond water and apply 30-40 kg of quicklime per mu for disinfection. After fertilizing the water by conventional methods, put the removed fingerlings back into the pond.

Size classification and rational mixing. For intensive fingerling rearing, fingerlings of different sizes should be stocked in separate ponds, and different species should be rationally mixed. For example, a pond mainly for silver carp and bighead carp fingerlings can be mixed with 30% grass carp fingerlings; a pond mainly for grass carp fingerlings can be mixed with 30% silver carp and bighead carp fingerlings. The ratio of silver carp to bighead carp fingerlings should be 5:1. If bighead carp fingerlings are smaller, the proportion can be reduced further; otherwise they will not grow large. For ponds rearing these three species, stocking density should not be too high. Generally, for a pond about 1.5 m deep, 3,000-5,000 fish per mu is appropriate.

Rational fertilization and increased feeding. For ponds mainly rearing silver carp and bighead carp, more fertilizer should be applied to maintain suitable water fertility, and some fine feed should be appropriately provided. The method is: apply human and livestock manure or chemical fertilizer once every 2-3 days, splashing about 50 kg of wet manure each time. For chemical fertilizer, use a nitrogen-phosphorus-potassium ratio of 1:1:0.5, applying a total of 5-8 kg per mu, dissolved in water and splashed evenly. Fine feed should be given around 9 a.m. and 4 p.m. each day, with 0.25-0.5 kg of wheat bran, rice bran, soybean cake, etc. per 1,000 fingerlings each time. For ponds mainly rearing grass carp, feeding should be strengthened. First feed green feed such as duckweed, aquatic plants, terrestrial grasses or grass pulp, then feed fine feed, to avoid grass carp competing with silver carp and bighead carp for fine feed.

Scientific management and fish disease prevention. Generally, replace with new water once a week, each time to a depth of 10-15 cm. For ponds mainly rearing grass carp, promptly remove residual scraps and leftover bait to keep water quality fresh. Frequently scrub the feeding platform, disinfect with bleaching powder once every half month, and regularly hang baskets and bags of bleaching powder, copper sulfate, etc. in the pond. Persist in patrolling the pond every day and observe the fish's feeding and activity. Once dead fish are found, promptly remove them for examination and use targeted drugs for treatment.