Cages used in aquaculture come in two main sizes: 4m² and 25m², each designed for different farming methods. The smaller 4m² cage measures 2m x 2m x 1.7m, with a depth of 1.5m below the water surface. The larger 25m² cage is 5m x 5m x 3.5m, submerged to a depth of 3m. These cages are constructed using 3x3 or 3x4 mesh polyethylene netting. The outer mesh has a size of 3.5–4.5 cm, while the inner mesh is 2.5–3.5 cm. A single-layer net covers the top of the cage, extending upward from the inner net. The cage is mounted on a square bamboo frame, which is 60–120 cm wider than the cage itself to ensure proper net expansion. The bottom of the cage is suspended at the four corners to keep it level, allowing for efficient water exchange. This setup enables fish to swim freely within the enclosure.
For small cages, the feeding system typically includes a feeding tube and an underwater food platform. A 40-mesh polyethylene net is placed at the bottom of the cage, attached to both the base and walls. The opening of this platform is 30 cm above the floor. Feed is delivered via a 1.9-meter-long, 12-cm-diameter plastic tube, ensuring even distribution. A mesh layer at the bottom prevents feed loss and keeps tilapia from entering the pipe. For floating feed, a surface food platform made of reinforced steel and mesh is used, positioned centrally in the cage. It floats 30 cm below the surface and is secured to the cage’s cover net.
When selecting a site for cage placement, factors like water quality, flow, and accessibility are crucial. The reservoir should be clean, with water transparency over 1 meter and dissolved oxygen above 5 mg/L. Cages should be placed in areas with minimal wave action, good water circulation, and a current less than 0.2 m/s. Avoiding major channels helps reduce turbulence. Cages are usually tied in groups using thick ropes or cables and anchored to trees or cement piles. Small cages are arranged in single rows, spaced more than 4 meters apart, while large cages are grouped in sets of three, spaced at least 30 meters apart.
Fish stocking typically occurs between late April and May when water temperatures stabilize above 20°C. Before stocking, cages must be checked for damage and properly secured. Fish should be healthy, uniform in size, and disinfected in a 3–5% salt solution before being carefully introduced into the cages. In small 4m² cages, 500–1,000 fish weighing over 20g are stocked, while 25m² cages can hold 3,000–4,000 fish, depending on conditions and management practices.
Feeding strategies vary based on fish size. Young fingerlings (around 50g) require 2–3mm feed with 30–32% crude protein. As they grow to 100g, the feed size increases to 3–7mm with 28–30% protein. Moldy or contaminated feed should be avoided. Large cages are fed manually, with feed scattered in the center of the cage. Small cages use either floating or sinking feed systems, depending on the type. Feeding frequency changes with water temperature: twice daily in spring (2–3% feed rate), 3–5 times in summer (3–7%), and once or twice in autumn (3–11%).
Daily management involves checking nets for damage, cleaning them monthly, and adjusting cage positions as water levels change. Observing fish behavior, feeding patterns, and water quality is essential. Disease prevention includes regular disinfection with bleaching powder and maintaining clean feeding equipment. If disease occurs, prompt treatment is necessary.
Harvesting typically takes place between May and July, when tilapia reach marketable sizes of 0.5–1.6 kg. A 4m² cage can yield up to 500 kg, while a 25m² cage produces around 2,000 kg. With proper management, one worker can handle 150 small cages, producing 75 tons of tilapia, or 12 large cages, yielding 24 tons. Profit margins are significant, with per capita production values reaching 600,000 yuan and profits of 150,000 yuan for small cages, and 200,000 yuan with 50,000 yuan profit for large ones.
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