Detailed Explanation of Key Technical Points for Grass Carp Cage Culture

For cage culture of grass carp, it is advisable to choose a location that is sheltered from the wind and facing the sun, with an open water surface, stable water level, fresh water quality, unpolluted water source, and convenient transportation. The water body should be rich in dissolved oxygen, with a pH value of 7.0-8.5, a water depth of 4 m-5 m, water transparency above 50 cm, and dissolved oxygen at around 5 mg/L. The culture area should have complete water conservancy facilities, capable of both drainage and irrigation, and not easily affected by floods. Now let us take a look at grass carp cage culture technology together!

Cage Configuration Methods

1. Cage equipment: The cage should be woven from polyethylene netting in a double-layer structure. The cage specifications can be 5 m × 5 m × 3 m. The cover net is single-layered with a mesh size of 5 cm and 3×4 thread. The inner layer mesh of the bottom net and side nets is 3 cm with 3×4 thread, and the outer layer mesh is 4 cm with 3×6 thread.

2. Cage installation: The cages are arranged in a “non” shape pattern, with one end fixed to the riverbank and the two corners at the other end fixed with concrete blocks weighing 100 kg each. The cage supports use galvanized steel pipes 6 m long, 40 mm in diameter, weighing 13 kg~14 kg, tied to oil drums with iron wire. At each of the four corners of every cage, a mineral water bottle filled with 2 kg of sand and gravel is attached as a sinker. The spacing between cages is 1 m, and the cage depth in water is 2 m.

3. Setting up fences: The cages should be installed and put into water 7 days before the fingerlings are stocked, allowing algae to grow on the netting to make the mesh smooth, so as to avoid the netting scratching the fish bodies after the fingerlings are placed in the cages. The arrangement direction of the cages should be perpendicular to the water flow direction. To prevent debris from damaging the cages, fences should be set up outside the culture water area.

Fingerling Stocking Methods

1. Superior fingerlings: The fingerlings should have a robust physique, uniform size, intact scales and fin rays, and be free of disease and injury. When stocking, it is advisable to use large-size fingerlings of over 20 cm.

2. Appropriate density: Generally, the grass carp stocked in cages should be 300 g-500 g per fish, with a stocking density of about 20-25 fish per sq m. A suitable number of silver carp and bighead carp fingerlings at 200 g-300 g per fish and blunt snout bream fingerlings at 100 g per fish can be polycultured in the cages.

3. Method matters: Before the fingerlings are placed in the cages, they should be bathed and disinfected to kill external parasites. They can be soaked in 3%-5% salt water or 20 g per cubic meter of potassium permanganate for 15 minutes. The stocking period is generally in late autumn or early winter, and stocking is best when the water temperature is around 15°C. At this time, after entering the cages, the grass carp can still feed and have a recovery period. After spring begins, they can start feeding early, increasing the fish growth time and laying the foundation for high yield and high efficiency.

Feed Management

1. Feed selection: When culturing grass carp in cages, it is generally not advisable to feed large amounts of grass, because grass has insufficient nutrition and can hardly promote growth. Instead, full-price pellet feed should be used to improve feed utilization and reduce water quality pollution from residual bait.

2. Feeding method: About two to three days after the grass carp are placed in the cages, domestication feeding can begin. The daily feeding amount is 3%-5% of the total fish body weight, fed three to four times per day, with each feeding lasting 0.5 hours-1 hour, until most fish are full and swim away. The feeding method should follow the “four fixed” principle. Feeding should be done by scattering small handfuls, and only after one handful is finished should the second be scattered. When the fish are not competing fiercely for food, feed slowly in small amounts so that weaker fish can also eat the feed and ensure balanced growth.

3. Strengthen feeding: Grass carp grow fastest at a water temperature of 25°C-30°C, so the feeding amount should be increased. In adverse weather such as rain, muggy heat, and thunderstorms, feeding should be reduced or stopped. Green feed can be disinfected with 1% bleaching powder and fed once every evening, with the feeding amount determined by no leftover grass the next day.

Routine Management of Grass Carp

1. Persist in cage inspection: Inspect the cages every day, regularly check fish growth, reasonably adjust the feeding amount, carefully observe and analyze fish conditions, and promptly handle any problems found. Wash and brush the cages once every 10 days-15 days, remove residual bait, debris, and attached algae, and ensure full water exchange.

2. Regularly inspect cages: Frequently check the cages and repair any damage in time to avoid fish escape or entry of predatory fish. During flood season, also promptly check rope strength, whether the cables are firm, and whether the netting is deformed.

3. Frequently adjust cages: As the reservoir water level rises and falls, the cages must be adjusted to positions with suitable water depth and water quality.

Fish Disease Prevention and Control Techniques

1. Prevention first: Persist in healthy culture, operate according to regulations, prevent disease before it occurs, do good prevention work, and carry out artificial immunization well. Generally, before entering the cages, inject inactivated vaccine for the grass carp “three major bacterial diseases” and inactivated vaccine for grass carp hemorrhagic disease. Before fingerlings are placed in cages, they should be disinfected with salt water. Regular disinfection and disease prevention are also needed. About every 10 days, feed medicinal bait such as Yubingkang and other Chinese herbal medicines once, for three to five consecutive days, to prevent the occurrence of bacterial fish diseases.

2. Purify water quality: Every 10 days-15 days, dissolve 250 g-500 g of quicklime in water for each cage and splash it across the entire cage while hot to purify the water quality.

3. Disinfect and sterilize: Every month, use insecticides and fungicides to splash across the entire cage. In high-temperature seasons, hanging bags around the cages can be used for disinfection and sterilization. Drugs can include bromochloro hydantoin, a mixture of copper sulfate and ferrous sulfate, etc., to promptly prevent and control water mold disease, red skin disease, gill rot disease, enteritis disease, and hemorrhagic disease.