How can polyculture ponds with grass carp as the main species achieve two high-yield seasons per year?
Grass carp is a typical herbivorous freshwater fish. The traditional farming method is feeding with hand-cut grass, producing one season per year. This farming model is labor-intensive, low-yielding and low-profit, generally producing 500-800 jin per mu, with a profit of only 800-1000 yuan per mu per year. Since 2003, the Fisheries Technology Extension Station of Gutian County, Fujian, has used automatic feeders in key fishery villages to deliver artificial pellet feed at fixed points, fixed times and intermittently for semi-mechanized pond farming with grass carp as the main species, producing two seasons per year. It achieved an average yield of 3,920 jin per mu, a survival rate of over 95%, and a profit of 3,000 yuan per mu per year, with one laborer able to manage 10 mu of ponds.
Pond selection
Choose ponds with sufficient water sources and no pollution sources upstream, convenient drainage and irrigation, and a constant slight flow of water year-round. Ponds should preferably be 5-10 mu in size, with a water depth of 1.5 m to 2 m.
Pond disinfection
10-15 days before stocking the fingerlings, disinfect the pond with water using 14 jin/mu·m to 20 jin/mu·m of bleaching powder, or splash the entire pond with 150 jin/mu·m of quicklime mixed with water while hot.
Fingerling stocking
1. First season: Start around the Spring Festival, mainly stocking grass carp fingerlings, with appropriate polyculture of bream, common carp, silver carp and bighead carp. Grass carp size 7-8 liang/fish, stocking density 600 fish/mu; bream size 4-5 liang/fish, stocking density 500 fish/mu; common carp size 2-3 liang/fish, stocking density 100 fish/mu; silver carp size 6-8 liang/fish, stocking density 100 fish/mu; bighead carp size 3-4 liang/fish, stocking density 20 fish/mu, to ensure all can be harvested and marketed before the Dragon Boat Festival.
2. Second season: Start after the Dragon Boat Festival, stocking only grass carp fingerlings weighing 3-4 liang each, at a stocking density of 600 fish/mu. By the end of the year, the fish generally reach over 2.5 jin each. Before stocking, all fingerlings are soaked and disinfected in a 4% saltwater solution for 10-15 minutes to prevent various bacterial diseases and saprolegniasis.
Feed feeding
1. Feed type: Choose sinking pellet feed specially for grass carp with a crude protein content of 28-30%. In the early breeding stage, the pellet diameter is 2.5 mm; in the late breeding stage, the pellet diameter is 3.5 mm. The feed conversion ratio is 1.6.
2. Installation and use of the automatic feeder: The automatic feeder can be installed at the pond edge next to the management house, with the power switch installed inside the management house. When feeding, simply turn on the indoor power switch, and the automatic feeder will evenly scatter pellet feed into the pond at set times and intermittently according to the programmed schedule. When feeding is finished (each feeding session is set to 1 hour), the power can be shut off automatically. One automatic feeder is sufficient for ponds within 10 mu.
3. Feeding method: The feeding ability of fish is closely related to water temperature. When the water temperature is low, the feeding ability of fish is weak; when the water temperature is high, the feeding ability of fish is strong. Therefore, in the early breeding stage, the daily feeding amount is calculated at 2-3% of the total weight of grass carp, bream and common carp in the pond, and in the late breeding stage it is changed to 5-6%. In muggy weather, cold waves, heavy rainstorms and similar conditions, the amount can be reduced as appropriate. Feed 2-4 times per day.
Daily management
For high-density intensive production models, daily management work is mainly to maintain good, stable water quality, with the focus on preventing oxygen deficiency and pond turnover.
1. Add fresh water: Keep a continuous small flow of water coming in day and night. When severe floating head occurs, increase the water inflow.
2. Patrol the pond earlier: Mild floating head starts from 5-6 a.m. and disappears after the sun comes out at 7-8 a.m.; this is normal. Severe floating head starts from 3 a.m. in the second half of the night. If measures are not taken in time, it will lead to pond turnover and fish death by 5-6 a.m. Therefore, get up at 3 a.m. in the second half of the night to patrol the pond once. Severe floating head is most likely to occur in the two solar terms of Xiaoman and Mangzhong. If severe floating head is found, measures such as adding fresh water and turning on the aerator to increase oxygen should be taken in time to prevent pond turnover.
3. Turn on the aerator at the appropriate time: For ponds under 10 mu, one 2.2 kW single-phase spray-type aerator is sufficient. During mild floating head, it can be turned on at 5-6 a.m. and turned off after the floating head disappears at 8-9 a.m. In the two solar terms of Xiaoman and Mangzhong, if there is thunderstorms or muggy weather, it should be turned on at midnight and turned off at 8-9 a.m. the next day.
Disease control
Adhere to the policy of "prevention first, prevention more important than treatment." During pond patrols, if grass carp are found gathering at the water inlet and the fish bodies appear darkened, this is a sign of disease onset. At this time, splash the entire pond with 1 mg/L bleaching powder for 2-3 consecutive days to stop the disease. Disease generally does not occur during the second-season culture period. The main diseases in first-season culture are the "three diseases" of grass carp and hemorrhagic disease of bream.