Detailed Explanation of Key Technical Points and Management Methods for Fish Fry Rearing
After the summer fry are divided into ponds, the 1-year-old fingerlings reared until the end of the year to a size of 12-15 cm and a body weight of 30-40 g are called spring fingerlings. The growth cycle of black carp and grass carp is 3-4 years, and in some places the 1-year-old fingerlings are reared into 500 g 2-year-old fingerlings.
1. Fingerling ponds: To rear large-size fingerlings, it is recommended to build dedicated fingerling ponds with an area of 3-5 mu and a water depth of about 2 m. The preparatory work before the summer fry are stocked into the ponds is the same as for fry ponds.
2. Stocking: There are two methods, monoculture and polyculture. Polyculture is generally adopted. For ponds mainly stocked with common carp: common carp 60%, grass carp 5%, silver carp 30%, bighead carp 5%; for ponds mainly stocked with silver carp: silver carp 60%, bighead carp 10%, common carp 20%, grass carp 10%; for ponds mainly stocked with grass carp: grass carp 60%, common carp 5%, silver carp 30%, bighead carp 5%.
3. Stocking density: It depends on the feed, rearing techniques, pond conditions, growth period and the size of the fingerlings at harvest. Monoculture stocking density: if 6,000 summer fry are stocked per mu, the reared size is 12-15 cm; if about 9,000 are stocked per mu, the reared size is 9-12 cm. Polyculture density can be calculated in proportion.
4. Daily management:
(1) For ponds mainly stocked with silver carp or bighead carp, basal fertilizer should be applied before stocking, and fertilizer should be applied as needed after stocking, along with a certain amount of grain feed; for ponds mainly stocked with grass carp and bream, green feed is the main feed, with an appropriate amount of concentrated feed; for ponds mainly stocked with common carp, pelleted feed is fed; for ponds mainly stocked with black carp, green manure or manure is applied.
(2) Adhere to the "four observations" (observe the season, observe the weather, observe the water, observe the fish) and the "four fixeds" (fixed time, fixed quantity, fixed quality, fixed location) principles when feeding. In early spring and late autumn when water temperature is low, feed less; feed more on sunny days, feed less on cloudy and rainy days, do not feed in heavy rain; feed less when the water is fertile, feed more when the water is lean; feed more when feeding activity is vigorous, feed less when appetite is poor. Feed twice a day, once in the morning and once in the afternoon, at fixed times. The feeding amount should be relatively fixed and must not fluctuate. The feed should be fresh, clean and palatable, and feeding should be done at a fixed location.
(3) Daily management is the same as for fry stocking. Feeding platforms should be disinfected to prevent fish diseases.
5. Pond merging and overwintering: In late autumn and early winter, when the water temperature is below 10°C, merge the fish into ponds by species and size. Winters in northern China are long and the climate is cold, so it is essential to ensure the safe overwintering of the fingerlings. In overwintering ponds, do not apply organic fertilizer after August; regulate water quality before freezing, that is, drain 2/3 of the old pond water, add new water, and apply inorganic fertilizer, with 2-3 kg of urea applied per mu, keeping the water transparency at about 30 cm. In winter, clear the snow from the ice surface to allow sunlight to penetrate; after the ice forms, change 20 cm of water each month.