In reservoirs with nutrient-rich water, using cages to raise fish species like white cardinal fish without feeding them is not only practical but also offers advantages such as not occupying pond space, eliminating the need for feeding, and keeping costs low. When raising a 13cm white cardinal fish in cages, the cost is less than 0.10 yuan, while raising the same size fish in ponds costs over 0.10 yuan. In terms of density, about 150,000 fish per mu (approximately 0.067 hectares) can be raised in cages, which is 30–40 times more than in traditional ponds. Therefore, raising fish in reservoir cages without feeding not only produces large fish but also ensures low costs and significant economic returns.
The success of this method lies in its ecological and physiological foundations. Ecologically, reservoirs are large bodies of water with strong water flow that maintains stable conditions within the cage, even with high fish density. Physiologically, fish tend to stay in a concentrated area, reducing their activity and allowing nutrients to accumulate, which promotes faster growth.
Here are the main techniques used in cage farming:
First, cage selection. Polyethylene mesh is commonly used, with sizes ranging from 30m² to 50m² and depths between 2m and 3m. These dimensions are ideal for ease of management. The mesh size should be adjusted as the fish grow. For example, when raising 4cm summer flowers, a 1.1cm mesh is suitable, and when they reach 13cm, a 3cm mesh can be used instead.
Second, location selection. Cages should be placed in calm areas, preferably facing north-south, with a depth of around 4m. These locations typically have higher plankton concentrations, which support natural feeding. A slight water current is beneficial, but if it exceeds 2m/s, the fish will swim against the current, using energy unnecessarily and hindering growth.
Third, cage density. Even in good water quality, cage area should not exceed 1% of the total water surface. The spacing between cages should be at least 30 meters apart, as there is no artificial feeding, and the natural plankton supply is limited.
Fourth, stocking density and species mix. The number of fry stocked and the combination of species depend on the plankton composition and water exchange in the reservoir. Generally, 200 to 300 fry per cubic meter of water is appropriate. If the water is rich in small plankton, white cardinal fish are preferred. If larger plankton dominates, then species like silver carp may be more suitable.
Fifth, daily management. Regular checks of the cages are essential. Over time, algae and other organisms attach to the mesh, blocking water flow. Cleaning methods include mechanical washing every two weeks, sun exposure, biological removal using tilapia or other fish, chemical treatments with copper salts, and submerging the cages to prevent photosynthesis by limiting light exposure. These steps help maintain optimal conditions for fish growth.
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