Wintering Technology of Tilapia Fish Species in Greenhouse

Winter breeding technology involves a series of carefully planned and managed practices to ensure the healthy growth and survival of fish during colder months. The process begins with the preparation of greenhouses, which are essential for maintaining stable water temperatures and protecting fish from harsh weather conditions. The greenhouses used in this system are rectangular structures measuring 34 meters in length and 23 meters in width. The indoor pond area covers approximately one acre, with stone walls and an earthy bottom that reaches a depth of 3.0 meters. These ponds are equipped with intake and drainage systems, as well as an impeller aeration machine with a power rating of 1.5 kilowatts. A plastic film covers the top of the greenhouse, helping to regulate internal temperature and provide a controlled environment for fish rearing. For fingerling sourcing, the Anoxilus species used in this operation is divided into two size categories: large (average weight of 42 g/tail, making up 80% of the stock) and small (average weight of 25 g/tail, accounting for 20%). The male ratio among these fish is over 93%, ensuring better growth performance and production efficiency. Before stocking, the greenhouses are cleaned in mid-September, and any damaged structures are repaired. Plastic film is applied in late September to seal the structure. Meanwhile, the pond itself is cleared of sludge using a mud pump, then disinfected with calcium oxide at a rate of 100–150 g/m³. After a seven-day disinfection period, the pond is refilled with water to a depth of 1.5 meters. The water source includes cold well water (at 27°C) and existing pond water, with a 40-mesh sieve installed at the inlet to prevent unwanted organisms from entering. Once the water is in place, it is treated with 1 g/m³ of bleach, and an aerator is installed to maintain good water circulation. Fingerlings are stocked between September 20th and 30th. Prior to transfer, they are fasted for three days to reduce stress. Fish are sorted by size and only those of similar sizes are stocked together in the same greenhouse. Before introduction, the fish are bathed in a solution of copper sulfate (8 mg/L) and bleach (10 mg/L) for 5–10 minutes to prevent disease. Water temperature in the greenhouse and the fish transport container must not differ by more than 3°C to avoid shock. Stocking density is maintained at 45–50 fish per square meter. During the pre-culture phase (late September to mid-November), the focus is on feeding, water quality control, and disease prevention. Feeding is done twice daily with self-developed compound feed containing 31–32% crude protein and 5–6% crude fat. Large fish receive 2.0 mm-sized pellets at a rate of 2.0–2.5%, while smaller fish get 1.5 mm-sized feed at 2.5–3.0%. Each feeding session lasts about 30–40 minutes, followed by 20–25 minutes of monitoring to ensure full consumption. Water changes occur every 2–3 days, with about 30% of the water replaced depending on factors like temperature, dissolved oxygen, and feeding activity. Aerators are used for 1 hour during sunny days and 5–7 hours at night to maintain oxygen levels. By mid-October, the water level is raised to 1.8 meters, and the water quality is adjusted to maintain a temperature of 22–23°C, dissolved oxygen of 3–4 mg/L, and transparency of 30–35 cm. Disease management includes treating fungal infections with Quanchiposa and administering florfenicol for 5 consecutive days. For trichodermosis, a copper sulfate and ferrous sulfate mixture is used, along with increased water exchange and continued feeding. During the middle phase (late November to early March), feeding continues with higher-energy feed (28% crude protein, 7–8% crude fat). Feeding frequency is reduced to 1–2 times per day, with lower feeding rates to maintain fish health in low temperatures. Water levels are kept at 2.0 meters, and water changes occur every 1–2 days. In the final stage (mid-March to early May), water changes are made daily, and photosynthetic bacteria are added every 15 days to improve water quality. Aerator use is adjusted based on sunlight and time of day to keep dissolved oxygen at around 3.0 mg/L. As temperatures rise, the greenhouse film is gradually removed to allow natural cooling, and the water temperature is maintained at 21–23°C. Fish diseases such as bacterial gill disease, enteritis, and fatty liver are monitored and treated accordingly. Bacterial gill disease is addressed with sodium dichloroisocyanurate, while fatty liver is managed through dietary adjustments. To improve efficiency, the author suggests several technical upgrades. First, water recycling using ozone treatment and biological purification can reduce hot water usage by 30–40%. Second, increasing the male ratio to over 95% enhances growth and reduces the need for smaller fish. Finally, improving fry specifications by extending the cultivation period through greenhouse and outdoor pond relay systems can increase fingerling size, reduce feed costs, and lower overall production expenses.

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