Safe Transport Methods and Precautions for Spring Fish Stock
Early spring is the season for releasing fry and fingerlings, and transporting fry and fingerlings between locations has become an important part of shallow-water aquaculture production. Transport must be safe and efficient, and the survival rate during transport must be ensured and improved.
When selecting fingerlings, choose those with thick flesh on the back and tail, a robust body, bright coloration, intact scales and fin rays, no wounds or parasites on the body surface, active swimming in the net cage, a strong ability to swim against the current, and that gather densely in one spot of the cage with heads down and tails up, straining against the water flow.
Transport of fry and fingerlings
Plastic bag oxygen-filled transport. The specifications of plastic fry bags are 70 cm x 40 cm. At a water temperature of 20 degC to 25 degC, each bag can hold 80,000 to 100,000 fry, 5,000 to 7,000 wuzai, or 1,200 to 1,500 summer fry; or it can hold 600 to 800 fingerlings 5 cm to 7 cm long, or 300 to 500 fingerlings 7 cm to 8 cm long, and can ensure a survival rate of about 90 percent within 24 hours.
Open-mouth canvas basket transport. At a water temperature of about 20 degC, each basket (0.4 cu m to 0.5 cu m) can generally hold 200,000 to 300,000 fry, 10,000 wuzai, or 14,000 to 18,000 summer fry; or it can hold 3,000 to 4,000 fingerlings 8 cm to 10 cm long. If oxygen supply is available, the density can be increased by 40 percent to 50 percent.
Canvas basket lined with a plastic bag and filled with oxygen for transport. Line a large plastic bag inside the canvas basket, with the bag height at least twice the basket height. Fill with clean water to one-half the basket height, then load the fish, squeeze out the air in the basket, then fill with oxygen, and tie the bag mouth tightly for transport. The fish-loading density is 2.5 times that of open-mouth transport.
Precautions for transporting fry and fingerlings. Before transport, formulate a careful transport plan; prepare tools and medicines for loading and unloading, starting transport and disinfection, as well as a disinfected pond; and prepare oxygen supply equipment. The transport density should be comprehensively determined according to the fish species, size, water temperature, water quality, transport time, transport method and oxygen supply equipment. Generally, the weight ratio of fingerlings to water is preferably 1:4 to 1:5. Choose clear days with lower air temperatures for transporting fingerlings. Feeding should be stopped 2 to 3 days before starting transport, and the fish should be concentrated with a seine net 2 to 3 times. Fingerlings should be seined and held in a temporary holding box 2 to 3 hours before loading and transport. Strictly grade the fingerlings with a sieve, remove wild and miscellaneous fish, and ensure uniform size. During transport, frequently observe the fish's activity and adjust the oxygen supply. Generally, change the water once every 5 to 8 hours, draining the old water to about one-third before adding new water. Once fingerlings are found to be short of oxygen, oxygen should be supplied promptly. After the fingerlings arrive, ensure that "people wait for the fish" and "water waits for the fish." Before the fingerlings are put into the pond, they should be soaked and disinfected with medicine.