Three-dimensional nesting and efficient technology of reservoir cages

In order to promote the industrialization of fish farming and breeding, we initiated ecological breeding experiments and technical demonstrations for cage-raised catfish in Qingjiang Reservoir, Hubei Province, starting from 2007. The project achieved significant success, and the key technical aspects are outlined below. First, the materials and methods used in the project were carefully selected and implemented. 1. Water Conditions The reservoir provides an ideal environment for aquaculture. The water has a high transparency of over 250 meters, with a pH level between 7.3 and 8.5, and dissolved oxygen levels ranging from 6.5 to 8.5 mg/L. The average depth of the water is about 65 meters, with clean water and minimal sediment. During flood season, the water flows rapidly, but the surface temperature remains stable between 8°C and 28°C. The water temperature stays within 20°C to 26°C for approximately 185 days annually, ensuring a strong self-cleaning capacity. The area is free from large docks, factories, or sources of pollution, making it suitable for high-quality fish farming. 2. Cage Setup The rigid cages were designed to accommodate fluctuations in water levels. They were arranged in a “non”-shaped frame for easy management. To ensure stability, fixed piles, cables, and other facilities were installed based on the maximum water level drop and storm resistance requirements. Before stocking, fingerlings were soaked in nets for 15 days, and the net bodies were installed 7 days prior to allow algae growth, which makes the net softer and easier for fingerlings to enter. All nets were inspected for damage, aging, and secure stitching before submersion. The cage dimensions were 4m x 3.5m x 3.5m and 4m x 4m x 4.5m. A double-layer net was used, with inner mesh size of 2.5 cm and outer mesh of 3.0–4.0 cm. The top of the cage extended 50 cm above the water, and the openings matched the frame size. Polyethylene ropes were used to secure the upper edges. Cages were spaced 50 cm apart, and sandbags were placed at the corners to prevent deformation. The test cages were open-type double-layer nets. 3. Fish Stocking Fish fingerlings were sourced from large-scale farms in Hubei, with sizes ranging from 15 to 18 cm and weights of 50 g per tail. They were stocked in the inner cages. Other species, such as filter-feeding and predatory fish, were obtained from semi-commercial ponds in Jianghan. Fingerlings were transported using oxygenated live fish tanks or bags, with a temperature difference of less than 5°C between the source and destination. Fish were fasted for two days before transport, and water temperature and oxygen levels were closely monitored during transit. Stocking was done early in the morning or during cloudy or rainy weather to reduce stress. On February 18, 2007, 12,000 high-quality fingerlings were introduced, including 50 g/tail catfish, 500 g/tail carp, 30 g/tail tilapia, and 100 g/tail koi. Koi served as "signal fish" to detect any damage to the cages. Before stocking, fish were disinfected in povidone iodine (3–5 mg/L) for 15–20 minutes, then treated with formalin (2‰–3‰) for 2–10 hours, and finally rinsed in 10–20 minutes of fresh water. 4. Feeding Management Feeding began 1–2 days after stocking, using compound feed with about 36% protein. The feeding amount was adjusted based on water temperature, weather, and fish condition, typically 2–3% of body weight. Feedings were conducted twice daily, with reduced frequency during high temperatures and winter. Regular patrols were carried out to monitor signal fish and repair or replace damaged nets. Attachments to the cages were checked, and if excessive, they were cleaned manually or replaced. Daily records were kept, documenting weather, water temperature, feeding, fish growth, disease prevention, and mortality. 5. Disease Prevention Fingerlings were sterilized 5–7 days before transport, and water-soluble vitamins were added to reduce stress. Fish were disinfected before entering the cages. During rearing, diseases were prevented by adding Chinese herbal medicine and vitamin mixtures to feed, along with external disinfectants like chlorine dioxide and bromine chloride. Second, the harvest and economic results were impressive. 1. Harvest Statistics After 10 months of cultivation, fish were harvested on December 19, 2007. A total of 10,500 fish were collected, averaging 650 g/tail, totaling 6,825 kg, with a yield of 48.75 kg/m². The survival rate was 87.5%. Squid harvested from the cages weighed 1,400 g, with each squid averaging 1,750 g. Tilapia and koi were also collected, with 200 kg of tilapia at 200 g/tail and 10 tails of koi at 100 g/tail. 2. Economic Benefits The total revenue reached 82,250 yuan, while total costs were 57,400 yuan, resulting in a profit of 24,850 yuan. The unit profit was 155.3 yuan/m³, and the input-output ratio was 1:1.43. Third, analysis and discussion revealed several key points. 1. Net Cage Effectiveness Cage farming proved highly effective for spot and tail catfish, which are in high demand and have a short breeding cycle. Compared to other species, catfish had the highest net profit. By using this technology, market supply was ensured, seasonal price differences were utilized, and natural resources were protected. This method also reduced water pollution and improved economic returns. 2. Importance of Fish Quality High-quality fingerlings are essential for successful cage farming. Only those from certified hatcheries with good health and growth performance were selected. These fish had higher survival rates, faster growth, and better disease resistance. 3. Rational Stocking of Filter and Shade Fish Filter-feeding and non-competitive fish were stocked alongside catfish to optimize space and utilize natural food sources. This helped purify the water, reduce disease risks, remove algae, and improve overall efficiency. This project demonstrated that ecological cage farming can be both economically viable and environmentally sustainable, offering a promising model for future aquaculture development.

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