Practical Experience Sharing on Temporary Rearing of Yellow Catfish Fry
The temporary rearing and cultivation stage of yellow catfish fry refers to the brief process in which newly hatched larvae that cannot swim freely are cultivated with careful nursing methods into individuals that can swim and feed on their own. The temporary rearing and cultivation of fry is also called larval-stage temporary rearing.
(1) Facility conditions
The characteristic of temporary rearing and cultivation of fry is that the time is relatively short and the temporary rearing area is relatively small. It can be carried out in hatching facilities, in small cages made of 30-40 mesh netting, or in cement hatching ponds and other facilities. No matter which facility is used, there must be a slight water flow condition, so that the larvae are not left motionless and caused to die.
(2) Cultivation methods
1. Cage temporary rearing The temporary rearing cage is processed into a rectangle with 40-50 mesh net cloth. The method is: first disinfect the pond to kill wild and miscellaneous fish, fill with water to a depth of 0.6-0.8 m, and fertilize the pond water quality until a large number of zooplankton appear. When the water transparency is above 40 cm, fix the cage firmly with wooden (bamboo) stakes, and tie all the upper and lower parts of the cage firmly so that the cage does not shake in wind and waves. The upper opening of the cage should be 10-12 cm above the water surface. If slight water flow can be provided, stock 8,000-10,000 larvae per sq m; when there is no water flow, stock 3,000-5,000 fry per sq m in the cage. When the fry can swim freely, begin feeding egg yolk slurry for 2 days. When the fry have relatively strong activity ability and can normally feed on zooplankton in the water, sink the upper opening of the cage to about 10-15 cm below the water surface, allowing the fry to leave the cage automatically and enter the pond. About 1-2 days after the cage is sunk, remove the fry that have not left the cage and put them into the pond. Attention must be paid to maintaining good water quality in the pond. The water should not be turbid, so as to prevent mud from sticking to the fry's body and affecting normal activity, which could lead to death. Keep the dissolved oxygen content of the pond water above 5 mg/L.
2. Temporary rearing in flowing-water cement ponds Clean all debris and dirt from the flowing-water cement pond, fill with water to a depth of 0.6-0.8 m, and place larvae with yolk sacs into the cement pond at 15,000-20,000 larvae per cubic meter of water. For the first 2-3 days, it is only necessary to keep water flowing continuously to maintain sufficient oxygen. At this time, all the fry gather around the bottom of the pond. When the fry have absorbed most of their internal nutrients and begin to feed on exogenous nutrition, that is, when the fry swim freely in groups, begin feeding egg yolk for 1 day. From the second day, begin feeding a combination of egg yolk and zooplankton. Live bait such as rotifers, cladocerans and copepods gives better feeding results. The feeding method is small amounts given many times. During the cultivation process, sufficient oxygen must be maintained in the water. In addition to flowing water, use an air compressor to increase oxygen in the pond, and remove debris and feces from the cement pond once every 2 days.
3. Management Yellow catfish larvae have delicate bodies, poor adaptability to the environment, weak activity ability, and difficulty in starting to feed. Therefore, management during the temporary rearing stage requires care and caution.
(1) Pond patrols During the temporary rearing stage, the frequency of pond patrols should be increased, especially during the period from 4 a.m. to dawn, when patrols should be repeated, because during this period the dissolved oxygen content in the water is lowest and the fish's activity ability is poorest. During pond patrols, attention should be paid to water inflow and drainage, bait density, power supply, fish activity, water temperature variation range, and fish disease conditions.
(2) Water quality The water quality is required to be fresh, free of pollution and excessive organic matter, with a pH of 7-8, and a dissolved oxygen content of about 6 mg/L, with a minimum not lower than 5 mg/L. Incoming water must be filtered to prevent pollutants and harmful organisms from entering. To ensure dissolved oxygen content, an oxygen pump should be installed in the temporary rearing pond.
(3) Shading Yellow catfish fry and fingerlings are photophobic and like to live in a weak-light environment. Therefore, the temporary rearing pond should be shaded to give the yellow catfish larvae a suitable habitat space.
(4) Waste removal and water changes When there is a lot of residual bait and feces, waste should be removed by siphon method. During waste removal, be careful not to siphon too quickly and not to suck out the larvae. If yellow catfish are sucked out, they should be put back into the temporary rearing pond.