Detailed Explanation of Key Points for Grass Carp Cage Aquaculture Technology

In recent years, as the grass carp market has improved, grass carp farming, especially intensive farming such as cage culture, has become relatively common. How to achieve high yield and high efficiency in farming is a technology urgently needed by many farmers. Here, combining with practical experience, we discuss the key points of grass carp cage aquaculture technology:

Farming Conditions Must Be Suitable

For grass carp cage aquaculture, it is advisable to choose a place that is sheltered from the wind and faces the sun, with an open water surface, stable water level, fresh water quality, unpolluted water source, and convenient transportation. The water body is required to 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 farming area should have complete water conservancy facilities, capable of both drainage and irrigation, and not easily affected by floods.

Cage Setup Must Be Reasonable

The cage should be woven from polyethylene material, with a double-layer structure: the inner layer is a knotless cage (closed type), and the outer layer is a knotted cage (open type). The top cover net is a single layer. The inner mesh size is 3 cm-3.5 cm, and the outer mesh size is 4 cm. The cage specification can be 5 m×5 m×2.5 m. The frame of each cage is made by tying together 4 bamboo poles each 8 m long to support the entire cage. Sinkers are made of long stone strips, tied to the 4 bottom corners of the cage, so that the cage fully unfolds and takes shape in the water. The cage is fixed with cables. The cables are polyethylene thick ropes with a diameter of 4 cm. The cables stretch across the water surface, and after being pulled taut, are tied to fixed stakes on the shore. The two cables are 8 m apart. After the cage is fixed by the cables, the upper edge of the cage should be 20 cm-30 cm above the water surface. The cage should be installed and put into the water 10 days after the fingerlings are stocked, so that algae can grow on the netting, making the mesh smooth and preventing the netting from scratching the fish after the fingerlings enter the cage, because fingerlings are generally not adapted after entering the cage, are prone to colliding, and are easily scratched. Cages can be set up individually or in groups. For individual cage setup, the spacing between cages should be more than 25 m. When set up in groups, every 5-10 cages form a group in a series arrangement, either in a single row or double row. Within a group, the spacing between cages is 4 m, and the spacing between groups is about 100 m. 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 farming water area.

Fingerling Stocking Must Be Scientific

Fingerling stocking should grasp four aspects: First, the fingerlings should be excellent. The fingerlings are required to have a robust physique, uniform size, complete scales and fins, and no disease or injury. Fingerlings entering the cage must be healthy, avoid trauma, and prevent the netting from scraping off the fish body mucus, because the mucus on the fish body can bind and remove attached microorganisms and debris, and is the first barrier for the fish body to resist disease. Therefore, when selecting fish, smooth and slimy ones are preferable, while rough ones are not. When catching fish, one should follow the direction in which the fish are swimming, and must not grab them head-on, so as to avoid injury. Second, the size should be large. When releasing fish, it is advisable to release large-size fingerlings over 20 cm, which not only have strong disease resistance and high survival rate, but also have a short farming cycle and can be marketed by the end of the year. Third, the density should be appropriate. Generally, cage stocking of grass carp is at a size of 300 g/fish-500 g/fish, with a stocking rate of about 20 fish/sq m-25 fish/sq m. Within the cage, a suitable number of silver carp and bighead carp at a size of 200 g/fish-300 g/fish and bream fingerlings at a size of 100 g/fish can be polycultured as appropriate. Fourth, attention should be paid to methods. Before the fingerlings enter the cage, they should be bathed and disinfected to kill external parasites and reduce the probability of pathogen transmission. Generally, 3%-5% salt water or 20 ppm potassium permanganate can be used for soaking and washing for 15 minutes. The stocking time is generally in late autumn or early winter. Stocking is better when the water temperature is around 15°C. At this time, after entering the cage, grass carp can still feed and have a recovery period. After the beginning of spring, they can start feeding early, increasing the fish growth time and laying the foundation for high yield and high efficiency.

Feed Feeding Must Be Careful

In cage aquaculture of grass carp, it is generally not advisable to feed large amounts of grass, because grass has insufficient nutrition and it is difficult to promote their growth. Full-price pellet feed should be fed to improve feed utilization and reduce water quality pollution from residual bait. Grass carp can begin to be fed 2 days-3 days after entering the cage. Before feeding, domestication should be carried out, following the rhythm of “slow-fast-slow” and the feeding amount of “less-more-less”, domesticating for 1 hour-1.5 hours each day. After continuous domestication for 10 days, when most fish can float up to compete for food, normal feeding can begin. The daily feeding amount is 3%-5% of the total fish body weight, fed 3 times-4 times per day, about 0.5 hour-1 hour each time, with the degree being that most fingerlings are full and swim away. The feeding amount each time should also be reasonably adjusted according to changes in water temperature, weather changes, fish feeding and activity conditions, etc. In feeding methods, the “four fixed” principles should be observed. Feeding should be done by scattering small handfuls; after one handful is finished, scatter the second handful. When the fish are not competing fiercely for food, feed a small amount slowly, so that weaker fingerlings can also eat the feed and ensure balanced growth. Grass carp grow fastest at a water temperature of 25°C-34°C, and the feeding amount should be increased. In adverse weather such as cloudy and rainy, muggy, and thunderstorms, feeding should be reduced or stopped. Green feed can be fed once every evening, disinfected with 1% bleaching powder and then put into the cage, with the feeding amount based on no leftover grass the next day.