Code of Practice for High-yielding Breeding of Aulatis Tilapia Ponds

Tilapia, a tropical fish widely farmed in freshwater environments, is favored for its adaptability, high fertility, diverse feeding habits, strong disease resistance, efficient feed conversion, fast growth, and delicious meat. Among the various species, *Oreochromis niloticus* (Nile tilapia) is particularly popular among farmers due to its high male ratio, rapid population growth, and high yield. Maoming City in Guangdong Province has successfully leveraged its geographical and natural advantages to develop the tilapia aquaculture industry, achieving remarkable results. Tilapia farming has reached a significant scale in the city. In 2003, the area dedicated to tilapia monoculture and mixed culture reached 380,000 mu, with a total production of 13,003 tons—a 44.73% increase compared to 89,845 tons in 2001. This accounted for one-third of the province's total tilapia production, making Maoming the top producer of tilapia in Guangdong. Based on existing pond culture techniques and technical data on *Oreochromis niloticus*, operational procedures for high-yield tilapia farming have been developed and implemented. **Pond Conditions** - **Area and Depth**: The pond area should range from 5 to 25 mu, ideally 10 to 15 mu. Fingerling ponds should be 1.0–1.8 m deep, while adult fish ponds should be 2.5–3.0 m deep. The pond embankment should be 35–55 cm higher than the water surface. - **Shape**: Rectangular ponds oriented east-west are ideal for better ventilation and sunlight exposure. The aspect ratio should be between 1.5:1 and 3.0:1. - **Bottom**: The pond bottom should be flat, easy for netting operations, composed of loam or sandy loam soil, with silt depth controlled at 14–20 cm. The pond should retain water well without leakage. - **Water Source**: Surface water is preferred. Water quality must meet national standards (GB11607-89), with sufficient supply during peak seasons (May–November). A water exchange of 10–20% is recommended. Each pond should have an independent intake and drainage system, with water transparency around 30 cm. - **Power and Equipment**: Electric power should be at least 1 kW per mu. Diesel generators are recommended as backup. Ponds should be equipped with aerators—3 kW impeller or waterwheel types for larger ponds, and 1–3 kW jet aerators for smaller ones. Automatic feeders may be used if hard pellets are employed. All ponds must have proper water injection and drainage systems. **Preparation Before Stocking** - **Cleaning**: Ponds, bottoms, and inlet/outlet systems should be trimmed to prevent leaks. - **Sludge Removal**: Sludge should be removed annually, keeping it below 14–20 cm. - **Disinfection**: Two methods are commonly used: - Dry method: Leave 8–12 cm of water, add 4–5 kg of tea bran or 50–80 kg of quicklime per mu, expose for 3 days, then refill with filtered water. - Wet method: Use bleaching powder (30% available chlorine) at 13.5 kg per mu, resulting in 20 ppm concentration, or 100–150 kg of quicklime. - **Fertilization**: After water return, apply 250 kg of organic manure per acre, fermented and disinfected with 1–2% lime. Fertilize after 7 days. **Fish Seedlings** - **Source**: Fish stocks must be approved by the relevant authorities and come from licensed hatcheries. - **Quality**: Must be uniform in size (weight variation <10%), healthy, and free from injury or disease. Purebred *O. niloticus* and hybrid F1 strains are preferred, with over 85% male individuals. **Fry Cultivation** - **Breeding Ponds**: 2–3 mu in size, with 1.5 m depth, clean and disinfected before use. Water should be filled 7–8 days before stocking, filtered through 40–60 mesh nets. Apply fertilizers and wait for plankton bloom before releasing fry. Increase water depth to 1.5 m after 10 days. - **Stocking**: Fry should be released when the temperature difference between transport and pond water is no more than ±2°C. Maintain water temperature above 22°C. - **Feeding**: First 3 days: live blood or cooked soybean powder. After 17 days: mix of soybean meal, rice bran, yellow powder, and low-flour feeds. - **Harvesting**: Fry grow to 3–5 cm in 20 days and can be moved to grow-out ponds. Stop feeding the day before harvesting. Use smooth nets and avoid hot sun during sorting. **Adult Fish Cultivation** - **Fertilization**: Apply 250 kg of organic manure per acre, fermented and disinfected. Release seedlings 7 days later. Water depth should be at least 1.5 m. - **Stocking Density**: 0.8–15,000 fry per acre, depending on size. - **Feeding**: Feed pelleted diets with 32% crude protein, 1.5–2 mm in size, twice daily (8–9 am and 5–6 pm). Daily feeding rate is 7–8% of body weight. - **Growth**: After 20 days, fish reach 10–11 cm and 25–50 g in weight. - **Disinfection**: Soak in salt (2–4%) for 5–10 minutes, bleach (10–20 ppm) for 10 minutes, or penicillin (80,000 units/50L) for 5–10 minutes. - **Sorting**: Stop feeding the day before. Use 12-mesh nets for sorting on sunny mornings. **Water Quality Management** - **Transparency**: Maintain between 25–35 cm through fertilization, water exchange, and liming. - **pH**: Keep between 7.0–8.0. Use quicklime to adjust pH, especially in acidic conditions. Apply 7.5–15 kg/mu monthly. - **Dissolved Oxygen**: Above 3 mg/L for 24 hours, no less than 5 mg/L for 16 hours. Use aerators, biological oxygen, and regular water changes. - **Aeration**: Equip each pond with 0.3 kW of aeration capacity. Run aerators twice daily: noon to 2 pm and 2–4 am. - **Avoid "Old Water"**: Add fresh water or increase aeration. Use lime or copper sulfate to treat old water. **Harvesting** - Fish should be sold when they reach marketable size. Stop feeding the day before harvest. Avoid over-sorting to minimize fish damage. **Disease Prevention** Tilapia is prone to gill disease, ulcers, and cold shock. Prevent sudden temperature changes and avoid antibiotics. Use sulfa drugs for prevention. In high-temperature conditions, ascites and red fin diseases may occur. Treat with 15 ppm lime or antibiotics as needed.

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