A farming method for cage polyculture of grass carp and silver carp in reservoirs

The so-called "cage-in-cage in reservoir cages" means placing 4 small cages inside 1 large cage, and "grass carp on top, silver carp below" means raising grass carp in the small cages and bighead carp in the upper and lower interlayers between the small cages and the large cage (the small cages are 5 m high, the large cage is 5.5 m high, and the interlayer is 0.5 m high). The grass carp in the small cages are intensively cultured at high density by feeding compound pellet feed, while the bighead carp in the large cage mainly use grass carp feces and drifted feed as bait, with no special feeding, in an extensive, low-density grazing-style culture. This farming model uses the different habits of different fish species to maximize feed utilization, adopts the cage-in-cage method to increase the three-dimensional aquaculture space in the water area and raise the unit aquaculture capacity of the water area, and is a new model and new technology that is energy-saving, high-density, and refined in regulation and rearing. Generally, 1 large cage of 10 m x 10 m x 5.5 m and 4 small cages of 5 m x 5 m x 5 m are used to stock 1,000 grass carp fingerlings of 100-250 g each, together with 70 bighead carp of 150-250 g each, and raise them for 1

year, when the grass carp can reach 2-3 kg per fish and the bighead carp can reach 1.5-2 kg per fish, with a survival rate above 95%.

1. Selection of water area.

1. Choose a reservoir bay near a village, facing the sun and sheltered from the wind, with a water depth of more than 15 m, to place the cages. This is both convenient for management and can prevent the cages from touching the bottom during the dry season (the normal fluctuation range of the water bottom is 3 m).

2. Choose a water area far from shipping lanes and wharves, with a current within 0.1 m/s. In this way, the water environment is relatively quiet and the stress response of the fish can be reduced.

3. Water areas with pollution sources such as chemical fertilizer plants, paper mills, and pesticide plants upstream and in surrounding areas should not be selected.

2. Making the cages.

1. Cage material: use 3 x 3 polyethylene knotted netting.

2. Cage specifications: the large cage is an open-top five-sided type, 10 m long, 10 m wide, and 5.5 m deep; the small cage is a closed six-sided type with a cover, 5 m long, 5 m wide, and 5 m deep; mesh size 3 cm.

3. Fishing raft structure: a bridge-raft-type fishing raft with a 5 m x 5 m frame built from large foam floats and pine boards. Generally, one fishing raft is installed with 5-10 large cages and 20-40 small cages.

3. Installation of the cages.

1. Fixing the large cage: after pulling the top rope of the large cage straight and taut, tie the corner ropes at the 4 corners to the pine board frame of the fishing raft, and use 0.25/7 x 3 polyethylene rope to wind and fix the perimeter of the cage's top rope to the edge of the frame; hang 3-5 kg heavy stones or sandbags on the outer sides of the 4 bottom corners of the cage so that the cage fully unfolds and takes shape in the water.

2. Fixing the small cages: install 4 small cages in each large cage. The fixing method for the small cages is the same as for the large cage.

3. Time for putting the cages into the water: the cages should be installed and put into the water 7-10 d before the fingerlings are placed in the cages, so that the netting becomes smooth after algae grow on it, thereby avoiding friction damage to the skin and scales of the fingerlings.

4. Stocking of fingerlings.

1. Stocking time: generally choose the period from after New Year's Day to the 15th day of the first lunar month of the following year to stock @#@233@#@ the fingerlings. During this period, the air temperature and water temperature are low, the fish body is firm, the scales are tight, and the fish do not like to struggle or jump, so the fingerlings are not easily damaged during operations such as netting, counting, and transport, and the survival rate after stocking is high. Stock grass carp fingerlings first, then bighead carp fingerlings.

2. Fingerling size: grass carp 100-250 g each; bighead carp 150-250 g each.

3. Stocking density: grass carp 120-200 fish/sq m; bighead carp 10 fish/sq m.

4. Concentrated holding: after the grass carp fingerlings are purchased and transported back, they should be soaked in a 3%-5% saline solution for 5-10 min, then held at a density of 600-1,000 fish/sq m in a few cages.

5. Vaccine injection: after the grass carp fingerlings have been held together until March-April, inject the "four-in-one" vaccine (a vaccine to prevent the four diseases of bacterial gill rot, enteritis, red skin disease, and hemorrhage), and raise them in separate cages according to the planned density.

5. Feeding method.

1. Feed type: throughout the entire farming cycle, feed only special sinking pellet feed for grass carp with a protein content of 28%-30%. In the early stage of farming, feed medium-sized pellets with a particle size of 2.5 mm; in the middle and late stages, feed large pellets with a particle size of 3.5 mm.

2. Daily feeding frequency and daily feeding amount: the feeding capacity of grass carp is closely related to factors such as water temperature, climate, and water environment. When the water temperature is low and the weather is abnormal, the feeding capacity of the fish is weak; when the water temperature is high, the weather is good, and the wind is calm, the feeding capacity of the fish is strong. From May to September, the water temperature is high and the climate is good, which is the golden season for grass carp growth. At this time, generally feed 3 times a day, and the daily feeding amount is 6%-8% of the total body weight of the grass carp; before May and after September, the air temperature is cold and the water temperature is low, so generally feed 2 times a day, and the daily feeding amount is 3%-5% of the total body weight of the grass carp. In case of abnormal weather such as muggy heat, cold waves, or strong wind and heavy rain, the number of meals and the amount can be reduced as appropriate.

3. Feeding method: feeding should follow the principles of "slow-fast-slow" and "little-many-little." In the initial stage, the fish school has not yet all risen to the surface to compete for food, so the feeding speed should be slower and the feeding amount should be smaller; in the middle stage, the fish school has all risen to the surface to compete for food and competes fiercely, so the feeding speed should be faster and the feeding amount should be larger; in the later stage, most of the fish school has already eaten enough and sunk down, leaving only a few small and weak ones that have not yet eaten enough, so the feeding speed can be slowed down and the feeding amount reduced. During feeding, methods such as splashing water or knocking on the frame can be used to make food-attracting sounds, so that they form a conditioned reflex and the fish school can rise to the surface promptly and as a whole to compete for food.

6. Daily management

Grass carp can feed on the algae attached to the cage walls, so there is no need to wash the cages during the farming period. Daily management work mainly consists of carefully observing and checking whether the netting is damaged or has loose knots, and repairing it promptly if so.

7. Disease prevention and control

After grass carp fingerlings are injected with the vaccine, their immune protection can last for more than 14 months, and they generally do not develop disease during the entire farming period. For safety, regular external disinfection for prevention can be maintained. The following 2 methods are mainly used in production for external disinfection:

1. Bleaching powder bag hanging disinfection: use small woven bags, each containing 150-250 g of bleaching powder, and hang them at the upper corners of the cage, with the medicine bags about 1 m into the water. Hang 2 bags per small cage, and add medicine once every 3-5 d.

2. Regularly splash quicklime: carry out disinfection once every 7-10 d, for 3 consecutive d each time, using 2-3 kg of quicklime per small cage each day, mixed with water and splashed while hot.