In reservoirs with nutrient-rich water, using cages to raise fish species like white cardinal without feeding is not only practical but also offers several advantages, such as not requiring traditional fish ponds, eliminating the need for additional feed, and keeping costs low. For example, when raising a 13cm white cardinal fish in a cage within a reservoir, the cost can be less than 0.10 yuan per fish, while raising the same size fish in a pond would cost over 0.10 yuan. In terms of density, about 150,000 fish per mu (approximately 0.067 hectares) can be raised in reservoir cages, which is 30 to 40 times more than what can be achieved in an inner pond. Therefore, raising fish in reservoir cages without feeding not only produces high-quality large fish but also ensures low costs and significant economic returns.
The success of this method is based on both ecological and physiological factors. Ecologically, reservoirs are large bodies of water with good water circulation, ensuring that the conditions inside the cage remain stable, even at high fish densities. Physiologically, when fish are concentrated in a small area, their activity levels decrease, allowing for better nutrient absorption and faster growth.
The main cultivation techniques include:
First, selecting the right cage. Polyethylene mesh is commonly used due to its durability and flexibility. Cages with an area of 30–50 square meters and a depth of 2–3 meters are ideal, as they are easy to manage. The mesh size should be adjusted as the fish grow. For instance, when starting with 4cm summer flowers, a 1.1cm mesh is suitable, and once the fish reach around 13cm, the mesh can be changed to 3cm.
Second, choosing the right location. Cages should be placed in calm areas, preferably facing north-south, with a depth of about 4 meters. 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 may swim near the surface, expending unnecessary energy and hindering growth.
Third, managing cage density. Even in good water quality, the total cage area should not exceed 1% of the reservoir’s surface area. The spacing between cages should be at least 30 meters apart, as there is a limit to how much plankton can naturally support fish without supplemental feeding.
Fourth, stocking density and species mix. The number of fry and the combination of species depend on the availability of plankton and the water exchange rate inside and outside the cage. Typically, 200–300 fry per cubic meter of water is ideal. If the water has a high concentration of small plankton, white pheasants are preferred. When larger plankton dominate, crabs or similar species are more suitable.
Fifth, daily management. Regular inspection of the cages is essential. Over time, algae and other organisms attach to the mesh, reducing water flow and affecting fish health. Cleaning methods include mechanical washing every two weeks, sun exposure, biological removal using tilapia or other cleaner fish, chemical treatments with copper salts, or submerging the cages in deeper water to prevent photosynthesis. These practices ensure the cages remain efficient and the fish thrive.
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