Key Technical Points for Grouper Culture in Earthen Ponds

Grouper is delicious and comes in a dazzling variety of forms, and is deeply loved by consumers everywhere. At present, cage culture is common in our country, but as the marine environment changes, cage culture suffers from more diseases that are difficult to control, so promoting grouper culture in earthen ponds is highly worthwhile.

1. Pond selection and silt removal 1. Pond selection Ponds of 5—20 mu each, 300 mu in total, with a water depth of 2—6 m; the bottom should be sandy or gravelly; tidal water intake should be convenient, the water fresh and clean, free of domestic and industrial pollution, and the maximum daily water exchange rate can reach 50%. 2. Pond clearing and disinfection Two months before stocking, drain the pond, dry it for 2 weeks, and remove silt and debris from the pond surface; install artificial reefs in the deep-water area using strip stone or rocks; install filter screens, fill with 50 cm of water, apply 150 kg of quicklime per mu and soak for 15 days for disinfection to kill pathogens and harmful organisms, then flush the pond twice with incoming water. 2. Basic feed cultivation Twenty days before stocking, fill with water to a depth of 0.4 cm, apply 500 g of urea, 50 g of superphosphate, and 25 g of silicate per mu for 3 consecutive times, so that the water color turns yellow-green, then gradually fill with water to 1 m, keeping transparency at about 0.4 m. 3. Fry stocking Grouper fry all come from natural fry caught in local sea areas, and the fry purchased are those caught by cage or by hook. When purchasing hook-caught fry, those with hook injuries or swallowed hooks should be discarded. The fry size is related to the stocking time: fry stocked in April weigh about 50 g each, and fry stocked in June weigh about 100 g each. The stocking density should be controlled within 667 fry/mu. 4. Feed feeding The feed is mainly fresh small trash fish and shrimp; when fresh feed is insufficient, compound feed is fed, once each morning and evening every day. When the water temperature is below 13°C, feed less or not at all, and no feed is given during the overwintering season. The daily feeding amount is 8%—10% of fish body weight in the early stage, and 5%—6% in the middle and late stages. The specific feeding amount is adjusted according to weather, water quality, feeding conditions, and the amount of leftover feed; generally, feeding conditions are checked through set feed frames, and the principle is to finish feeding within 2 hours. Feed at fixed times twice a day, at 6 a.m. and 5 p.m. The feeding location should be changed every 10 days to avoid deterioration of the local bottom sediment caused by long-term feeding at one spot, which would affect water quality. 5. Water quality management and disease control 1. Water quality control Regularly test the physical and chemical factors of the water. Through water exchange and splashing quicklime, keep transparency in the range of 0.3—0.5 m, pH at 7.8—8.5, dissolved oxygen above 5.0 mg/L, and ammonia nitrogen content below 0.5 mg/L. The daily water exchange rate is about 30%. In high-temperature seasons, according to tidal conditions, schedule water exchange in the evening or at dawn, and try to avoid draining water at noon. 2. Disease control Persist in disinfecting the pond water once a month with 0.3—0.5 g/cubic meter of Yuchongjing to kill parasites; about every half month, disinfect the pond water once with 25 g/cubic meter of quicklime or 0.3—0.5 g/cubic meter of Sandai Yuxia'an to kill pathogens; in summer, feed medicated bait with oxytetracycline or allicin for one treatment course each month to prevent the occurrence of diseases. 6. Culture results 1. Yield After nearly 2 years of culture, all grouper can be harvested. The largest individual grouper weighs 0.7 kg, the smallest individual weighs 0.3 kg, and the average individual weight is 0.5 kg. 2. Survival rate The survival rate throughout the process reaches about 66.1%. 3. Feed coefficient The feed coefficient for compound feed is 1.7, and the feed coefficient for fresh feed is 8.61. 4. Economic benefits The average selling price is about 100 yuan/kg, the output value per mu reaches 23,000 yuan, and after deducting costs of 13,000 yuan, the profit per mu is 10,000 yuan, with an input-output ratio of 1:1.75. 7. Other technical points 1. Grouper has the habit of cannibalism, so when stocking fry, the fry should be uniform in size and stocked all at once. If individual differences are large, they should be classified and cultured in separate ponds. Since the fry come from hook capture or cage capture, before entering the pond they should first be bathed in 10 mg/L potassium permanganate for 10 minutes to kill parasites and bacteria, prevent wound infection, increase the survival rate, and prevent disease occurrence. 2. When filling the pond with water, filter screens must be used to prevent harmful organisms from entering the pond. 3. Artificial reefs should be installed in the deep-water area of the pond to provide a good habitat for grouper. 4. In order to improve the physique of grouper and enhance disease resistance, in the early stage of culture, feed containing compound vitamins (vitamins C, E, A and trace elements) should be fed regularly. 5. In order to prevent leftover feed from polluting water quality, it is recommended to polyculture a small number of sparid fish to clear leftover feed and maintain good water quality.