Practical methods for rejuvenating weak fish fry in autumn

Due to the hot summer climate, aging water quality, and feeding management issues, many farmers' @#@233@#@ are in poor condition. If these weak fish fry are not rejuvenated promptly when the autumn weather turns clear and cool, it will not only be detrimental to their overwintering but will also greatly affect next year's production. Therefore, doing a good job of autumn rejuvenation of weak fish fry is very important. The methods for autumn rejuvenation of weak fish fry are introduced as follows:

Transferring ponds and clearing ponds

After the high-temperature seasons of spring and summer, water quality generally ages, natural organisms decrease, and harmful pathogens increase, which is extremely unfavorable for fish growth. After the beginning of autumn, fish fry should be transferred promptly to new ponds for cultivation and rejuvenation. If water sources and pond rotation are difficult, all fish from the old pond can be transferred out temporarily, more than half of the old water in the original pond can be replaced, and 20-30 kg of clear limewater solution per mu of water surface can be splashed over the entire pond for disinfection. After 7 days, fresh water can be added, and then the fish fry can be transferred back.

Separate rearing and sparse stocking

Fish fry should be reared separately according to different sizes. Generally, fish fry with a body length exceeding 15 cm can be put into main adult fish ponds for polyculture, while smaller fish fry should be placed in dedicated ponds for cultivation, making sure as much as possible that fish fry stocked in the same pond are of uniform size. At the same time, the stocking density of fish fry should be reduced, and fish species should be reasonably matched. Generally, for a pond with a water depth of 1.5 m, 5,000 fish fry within 10 cm can be stocked per mu, and by the end of the year they can generally grow to about 15 cm. In ponds mainly rearing silver carp and bighead carp fry, 30% grass carp can be polycultured; in ponds mainly rearing grass carp fry, 30% silver carp and bighead carp can be polycultured. Among these, the ratio of silver carp to bighead carp is best at 5:1.

Feeding and fertilizing

Starting from mid-September, the amount of feeding and fertilizing should be increased to ensure sufficient nutritional needs. In ponds mainly rearing grass carp fry with silver carp and bighead carp fry polycultured, generally 80 kg of fresh tender green grass should be fed per 10,000 fry per day, supplemented with about 2 kg of concentrated feed such as soybean cake, cornmeal, and bran. Be sure to feed the green feed first, then the concentrated feed, to prevent grass carp from competing for food with other fish. For ponds mainly rearing silver carp and bighead carp fry, in addition to appropriately increasing the amount of concentrated feed, organic fertilizer should also be applied promptly. Fertilizing is best done on sunny days, and the amount should depend on water quality, with small amounts applied more frequently being preferable. Generally, apply organic fertilizer once every week, with 50-60 kg of decomposed human and livestock manure per mu each time. Apply chemical fertilizer once every 2-3 days, 3-5 kg each time, with the application ratio of nitrogen:phosphorus:potassium = 1:1:0.5. After the chemical fertilizer is dissolved in water, splash it over the entire pond.

Pond inspection and disease prevention. To ensure good autumn fattening of fish fry, the first priority is to ensure they do not get sick. However, the autumn water temperature environment is suitable for the reproduction of various pathogenic microorganisms, making fish diseases prone to outbreaks. Large-sized fish fry are especially susceptible to hemorrhagic disease, enteritis, and gill rot. To prevent autumn fish diseases, first, inspect ponds frequently, especially during muggy weather and after heavy rain, and pay even more attention to preventing fish from oxygen deprivation, floating to the surface, and pond-wide die-offs. At the same time, observe the fish's feeding and activity; second, persist in promptly removing residual bait, and disinfect the feeding area and feeding tools once every 2 weeks by splashing water mixed with bleaching powder; third, improve water quality by draining part of the old water from the pond every 10-15 days and adding about 15 cm of fresh water, or alternatively splashing quicklime over the entire pond for disinfection about every 20 days.