Fish farming in cages mainly depends on the water quality and the source of feed. For water bodies with fatter water quality and richer natural foods, silver carp and bighead carp should be mainly farmed. Water bodies with thin water quality, transparency of more than 50 cm, and light water color are not suitable for breeding silver carp and bighead carp, and feed fish such as grass carp, carp, tilapia, California perch, osmanthus fragrans, etc.
(1) Preparatory work before the fish species are put into the fishing cages
Before launching the fishing cages, check the holes and seams carefully. The fishing cage must be installed 3-5 days before the fish species are put into the cage and put into the breeding water area. After the net is soaked and the epiphytic algae, the fishing cage can be fully expanded and the fish body can be avoided from scratching.
Ten days before the summer croaker enters the box, start to pull the net in the original pond to exercise, no less than 3 times, and the intensive time of exercise should be increased successively. This is one of the key measures to ensure the survival rate of the box. When the fry needs to be transported long distances, after 3 exercises, the fry to be transported are placed in a cloth pond set up in another fresh water pond, and after a night of hanging water, the fry will be transported the next morning to increase the survival rate of the fish.
(2) Stocking of fingerlings
1. Stocking of silver carp and bighead carp fingerlings
(1) Variety and matching ratio of stocking
When silver carp and bighead carp fingerlings are reared in cages in lakes, rivers, and reservoirs, the stocking ratio is also different due to the different natural food composition in the waters. In water bodies with fatter water quality, less transparency, and more phytoplankton, silver carp should be the mainstay, and bighead carp should be the supplement. Water bodies with more zooplankton are more transparent and should be mainly bighead carp and silver carp as a supplement. In addition, it is necessary to properly match about 5% of omnivorous and scraping fish such as tilapia, crucian carp, carp, carp or bream to remove the attached algae on the net wall.
(2) Stocking specifications
In general fishing cages, summer flower stocking specifications require more than 3 cm, which should be large rather than small. It is required to have neat specifications, bright body color, strong physique, and no damage to the body surface.
(3) Stocking density
Cultivation of fish species in cages is a high-density fishing, and the stocking density should be determined according to the amount of plankton in the water body, the amount of water exchange in the cage, and the level of breeding management technology. Generally, 50-200 summer flowers are stocked per cubic meter of cultivating fish species in the water, 200-400 fish can be stored in fatter water, 500-600 fish can be stored in particularly fertile water, and the box size is about 13 cm. When cultivating second-instar fingerlings, generally 20-60 fingerlings of 10-13 cm are stocked per cubic meter.
In fact, within a certain density range, increasing the stocking density can increase the production of fingerling populations, but the individual size of the fish species out of the box is smaller, and appropriately reducing the density can correspondingly increase the size of the fish species out of the box.
The level of management technology is related to the survival rate of fish species. At present, the survival rate of higher management technology can reach more than 80%, while most units are around 60%. In production, the death of fish species in cages mainly occurs in the early stage of entering the tank. The main cause of death is caused by careless operation during exercise and transportation, which caused the fish to be injured. Therefore, strict body surface disinfection should be carried out when the fish species are put into the box, and they shall be checked once a week or so after being put into the box and supplemented. It is best to put enough fingerlings at once.
According to our judgment on the production potential and the out-of-box specifications we require, referring to the survival rate index, the following formula can be used to calculate the stocking density.
Number of fingerlings per square meter = production capacity per square meter × number of fingerlings per kilogram ÷ fingerling survival rate.
2. Cage stocking and feeding fish
Cage stocking and feeding fish requires fresh water quality, low fertility, sufficient dissolved oxygen (5 mg oxygen/liter), and water flowing speed of about 0.2 m/s.
The stocking density of fed fish fingerlings can be much higher than that of silver carp and bighead carp fingerlings, which mainly depends on the amount of water exchange, the level of dissolved oxygen, the supply of feed and the species of culture. The water flow is large, the flow velocity is about 0.2 m/s, the water quality is good, the dissolved oxygen is high, the feed is sufficient, and the stocking capacity can reach 1000 fish/m2. The stocking density should not be too high in waters where the water exchange volume is small and the water quality is relatively fertile.
When cultivating fish species in cages, it is best to replace cages with different specifications in time as the fish grow. Generally, three sizes of cages are used from fingerling to growing fish. For example, fish species above the summer flower should be cultivated in a 1.1 cm net cage; for 8 cm fish species, use a 2 cm net cage; for 11-13 cm one-year-old fish species, use a 2.5-3 cm net cage Cage. For fish species over 20 cm, use a net cage with a mesh size of 5-6 cm. In this way, not only can the exchange of water in the cage be improved, but also the cost of the cage can be saved.