Technical Key Points for Cage Culture of Bighead Carp in Reservoirs

I. Cage Structure The cage material is polyethylene, the netting twine diameter is 1.13 mm, the mesh size is 3—5 cm, the cage specifications are 4 m x 7 m x 2 m, a single-layer cage is adopted, the frame is bamboo poles, the bamboo pole diameter is about 10 cm, several are connected as one unit, and fixed with sinkers.

II. Cage Placement The placement position of the cage is extremely important and directly affects the growth rate of bighead carp. Generally, it is advisable to place it in a reservoir area with broad water, slight flowing water, good water quality, no pollution, ample sunlight, shelter from wind and facing the sun, relatively high water temperature, abundant food organisms, relatively close to shore, water depth of 4—7 m, relatively small wind force, and convenient transportation.

III. Fingerling Stocking

1. Fingerling stocking time: November--December each year, or February—March of the following year, when the water temperature is relatively low, transportation is convenient, fish bodies are less injured, and the survival rate is high.

2. Fingerling stocking size: there are two types, about 80 g or about 350 g respectively.

3. Stocking quantity: for 80 g fingerlings, stock 450—550 fish per cage; for 350 g fingerlings, stock 200--250 fish per cage.

IV. Precautions: the water temperature for releasing fingerlings should be lower than 12 degrees Celsius; the fingerlings should be robust and uniform in size; strict disinfection should be carried out before and after entering the cage to prevent saprolegniasis and death. Before the fingerlings enter the cage, due to transportation and loading, the fish bodies are injured, and under relatively low water temperature conditions saprolegniasis is very likely to occur. IV. Feeding Management The success or failure of cage culture of bighead carp depends greatly on feeding management. Good management can accelerate the growth of bighead carp, increase yield, and obtain relatively good economic benefits. Otherwise, due to poor management, growth may be slow, or the fish may even escape, resulting in culture failure. Feeding management mainly includes the following aspects:

1. Soaking the cage: new cages have rough surfaces, and directly loading fish can easily injure the fish bodies. Therefore, they must be placed in the reservoir to soak 7—10 days in advance.

2. Brushing the cage: after the cage is placed in the reservoir, due to the action of plankton in the water, much dirt adheres to the cage, affecting water exchange and causing a decrease in the number of plankton in the cage, so bighead carp grow slowly due to a shortage of food organisms. Therefore, the cage must be brushed and washed frequently. Generally, during the growing season, brush and wash once every 15—20 days.

3. Moving: there are two situations for moving. First, during flood season, move the cage to prevent it from being smashed by floods and strong winds; second, by moving the cage, increase the content of food organisms in the cage and accelerate the growth of bighead carp.

4. Feeding: sometimes the reservoir water body is relatively lean or there are relatively many cages, and other methods cannot increase the food organisms in the cage. At this time, it is necessary to pile or hang organic fertilizer or chemical fertilizer around the cage. Chemical fertilizer is hung in windless conditions.

5. Cage splitting: after one year of culture, the fingerlings mostly grow 10—20 times. In the following spring, in order to ensure normal growth of the fish in the cage and avoid insufficient dissolved oxygen and food in the cage, the cage must be split.

6. Watching and management: during the growing season, the cage needs to be checked frequently, the activity of the fish observed, and measures taken promptly when problems are found to prevent fish from escaping. In winter, fish not yet sold should be gathered together for watching and management to prevent strong winds from breaking the cage or theft.

V. Harvest and Sales In November, when the reservoir water temperature drops to 10 degrees Celsius, bighead carp have stopped growing, and harvesting and sales of bighead carp begin. At this time, stocked 100 g bighead carp can grow to more than 500 g, and each cage can yield a net production of more than 200 kg of bighead carp; after cage splitting the following year, they can grow to more than 1500 g. Stocked 350 g bighead carp can grow to 1000 g, and each cage can yield a net production of more than 250 kg of bighead carp; after cage splitting the following year, they can grow to more than 2500 g. 1000 g bighead carp can be sold at 5 yuan/kg; bighead carp of more than 2000 g can be sold at 6.4 yuan/kg. Therefore, each cage of bighead carp, after one year of culture, can bring a net income of more than 1000 yuan. If each household among the people in the reservoir area cultures 4—10 cages, each year they can obtain a net income of 4000--10000 yuan.