Key Technical Points for Semi-Artificial Propagation and Culture of Yellow Catfish
Because the testes of male yellow catfish are dendritic in shape, semen cannot be squeezed out; therefore, in current fully artificial propagation, the usual practice is to kill the male fish, remove the testes, cut them into pieces, and perform artificial insemination, after which all the male fish die. After manual egg squeezing, the vast majority of female fish also die. The cost of broodstock for fully artificial propagation is relatively high, and the labor intensity is also relatively high. Semi-artificial propagation involves artificial induction of spawning and then allowing yellow catfish broodstock to naturally mate, spawn, and fertilize, with low labor intensity; the broodstock can be reused or sold, greatly reducing broodstock costs, and the spawning effect is very obvious, so it is worth promoting.
Broodstock selection Broodstock selection is generally carried out in winter, requiring male fish to weigh more than 100 grams each and female fish to weigh more than 75 grams each, with smooth body surface, no injuries or diseases, and complete fin rays, obtained by net capture or pond draining. The female-to-male ratio is selected and retained at 1:1.5.
Spawning pond preparation Cement ponds are best for spawning ponds, and the area should not be too large, with convenient water inlet and drainage and conditions for flowing or flushing water. Before spawning, carry out thorough cleaning, disinfect with a 20 mg/L potassium permanganate solution, rinse with clean water, and set aside for use.
Spawning nest preparation Select PVC pipes with a diameter of 15-30 cm, saw them into short pipes 35-45 cm long, cover one end well with 40-60 mesh sieve silk cloth, disinfect with a 20 mg/L potassium permanganate solution, and after cleaning, place them flat on the bottom of the spawning pond, fix them securely so they cannot move, with the end covered by sieve silk cloth facing the direction of water flow.
Induced spawning When the water temperature stabilizes above 22 degrees C and there are several consecutive clear days, select broodstock with better development for induced spawning. The female-to-male ratio of broodstock for induced spawning is 1:1.3-1.5. The first injection of spawning agent is given at 8 p.m., using 40-50 micrograms of LHRH-A2 plus 2,000-2,500 international units of HCG per kilogram of male fish body weight, and 60-70 micrograms of LHRH-A2 per kilogram of female fish body weight; the second injection is given at 7-8 a.m. the next day, using 80-90 micrograms of LHRH-A2 plus 4,000-5,000 international units of HCG per kilogram of female fish body weight, with no injection for male fish. Each fish is injected with 0.2-0.3 milliliters.
Management of broodstock after induced spawning Immediately after injection, place the broodstock into the spawning pond and maintain slight flowing water. About 8 hours after the second injection, increase the water flow. Check the spawning nests early the next morning; if eggs are found, immediately take out the spawning nest and place it into the hatching pond, and at the same time add one more spawning nest. After 48 hours, take out the spawning nests and broodstock.
Hatching After the spawning nests are taken out, place them into the hatching pond, and place one air stone at the pipe opening of each spawning nest for aeration. The water level of the hatching pond is controlled at 60-70 cm, with 1/3 of the water changed every 24 hours. During membrane shedding, change water promptly and maintain slight flowing water. At a water temperature of 24 degrees C, membrane shedding can occur in about 60 hours.
Management after membrane shedding After the fish eggs have completely shed their membranes, take out the spawning nests. Replace 1/2 of the water, siphon off dirt, and keep the water quality fresh. The temperature difference between the replacement fresh water and the original hatching pond water must not exceed 1 degrees C. Seventy-two hours after membrane shedding, first feed small rotifers, then gradually transition to feeding large rotifers and cladocerans.
Pond removal After 5-6 days of rearing, when the fry size reaches 1.2-1.5 cm, promptly move them into summer-fry culture ponds for culture or sell them.