Detailed Explanation of Key Points for Artificial Breeding of Mullet

Selection and cultivation of broodstock: In autumn or early winter, select intact and uninjured individuals from those caught in sea areas or from adult fish raised in seawater or brackish water as broodstock. Female fish should be 3 years old and weigh more than 1.5 kg; male fish should be 2 years old and weigh more than 1 kg. The broodstock pond area should not be too large, preferably 1500-2000 sq m, with a water depth of 1.5-2 m, access to seawater and freshwater sources, and convenient drainage and irrigation. The stocking density per mu of broodstock pond should not exceed 100 kg. Mullet begin to seek food in small amounts at a water temperature of 4°C, and more than 10% feed normally. In broodstock cultivation, the method of completely artificial feeding with commercial bait can be adopted, or the method of feeding combined with fertilizing the water can be used. Commercial bait types are preferably peanut cake, soybean cake, @#@245@#@ sprouts, and Acetes shrimp. Organic fertilizer should be used for fertilizing; chemical fertilizers are not suitable. The transparency of the broodstock pond should be controlled at around 30 cm. Before spawning, "salinity transition" and flowing water stimulation should be carried out. "Salinity transition" refers to introducing seawater into the broodstock cultivation pond in late autumn and spring for broodstock cultivated at a salinity below 5‰, gradually raising the pond water salinity to above 15‰, which is very effective for increasing the maturation rate of broodstock gonads. In addition, fresh water should be injected into the broodstock pond every half month to 20 days in autumn, every week to 10 days in spring, and every 2-3 days before spawning, draining old water while injecting, to promote broodstock appetite, reduce disease, and stimulate gonadal development.

Induced spawning: The optimal water temperature for induced spawning of mullet is 16%-20%. The induced spawning season runs from late April to mid-June, generally concentrated from late April to mid-to-late May. The timing of the induced spawning season is related to the quality of broodstock cultivation. The induced spawning drugs and dosage combinations can refer to the following (dosage per kg of fish body weight): carp or crucian carp pituitary alone 15-20 mg, HCG alone 2000-4000 IU, LRH-A alone 150-300 micrograms; or carp or crucian carp pituitary 5-10 mg + HCG 1000-2500 IU + LRH-A 100-150 micrograms, carp or crucian carp pituitary 10 mg + HCG 1500-2500 IU, carp or crucian carp pituitary 100 mg + LRH-A 100-300 micrograms. Generally, female fish are injected in 2 doses with a 24-hour interval; the first dose is 1/3 of the total, the second dose is 2/3 of the total. If spawning does not occur, an additional 1/2-2/3 of the total dosage can be supplemented. During the induced spawning process, flowing water stimulation with fresh water has a great impact on improving the induced spawning rate. Artificial insemination is so far the only method of mullet reproduction. The optimal time for mature eggs to maintain fertilizing capacity is at a water temperature of 16%-20°C; the characteristics of mature eggs are full and transparent egg spheres, with an egg diameter of about 1 mm, a large oil globule in the center with a diameter of 0.45-0.5 mm, uniform egg size, glossy and round, elastic, and showing a bright orange-yellow color; the egg flow characteristic is that when the abdomen is gently squeezed by hand, the eggs flow out smoothly without blood clots or egg masses. Both the dry method and semi-wet method can be used for insemination.

Hatching of fertilized eggs: At a salinity below 13‰, the eggs are demersal; above 15‰, they are pelagic. The hatching water temperature is 16°C-20°C. Both flowing water and still water can be used, but the hatching rate is higher with flowing water. The speed of embryonic development depends on the water temperature. At a water temperature of 16°C-20°C, embryonic development can be completed in 46-52 hours.

Fry and fingerling cultivation of mullet: At present, the fry-rearing techniques for cyprinid fish are mostly adopted, that is, in ponds, natural food organisms are propagated through fertilization while commercial bait is fed for cultivation.

Preparation of the fry pond: Before the fry are stocked into the pond, the fry pond must be thoroughly cleared with pond-clearing drugs. After pond clearing, 7-10 days before the fry are stocked, fill with water to 50-60 cm and apply base fertilizer to cultivate natural food organisms. Apply 3750-6000 kg of livestock and poultry manure per mu of water surface; use less in old ponds and apply sufficient amounts in new ponds. Ten days after applying the base fertilizer, plankton in the pond begins to propagate initially, reaching a peak in about half a month.

Stocking of fry: Mullet fry begin to swim horizontally 4-5 days after hatching and can actively feed, so they should be stocked into the nursery pond at the appropriate time, at a density of 80,000-120,000 fry per mu. When the fry are stocked, the water temperature difference between the hatching pond and the fry pond must not exceed 3°C; when the fry are stocked, the pond water salinity must not be lower than 7‰; the stocking time should be chosen on a clear and windless day, preferably at 3-4 p.m.; the fry should be stocked with water, and a "test water" should be conducted 1-2 days before stocking the fry to observe whether the fry activities are normal.

Feeding and management: Different feeding and management measures should be adopted according to the feeding habits of mullet fry at different stages. In the early stage, a method combining fertilization and spraying soybean milk is used. For every 10,000 fry, about 20-25 kg of soybean milk is used, and according to water quality conditions, additional fertilizer is applied 3-4 times, with a total additional fertilizer amount of 100-150 kg per mu. If the food organisms in the pond are not abundant enough, Artemia nauplii, rotifers, egg yolk, etc. can be added 10 days before fry rearing. When the fry grow to 1.5-2.0 cm, they enter the stage of mixed cultivation with animal and plant-based bait, feeding soybean cake, peanut cake paste, soybean residue, as well as cornmeal, rice bran, etc. As the fry gradually grow, the water volume in the nursery pond should be gradually increased, with each water addition of 15-20 cm, and fresh freshwater can be gradually introduced into the pond to reduce the pond water salinity. After 25-30 days of cultivation, the fry grow into 2.5-3 cm summer fingerlings and can fully adapt to living in freshwater. Summer fingerlings should be promptly trained by hauling with a net and transferred to ponds for sparse rearing, and can be transferred to fry cultivation ponds. Fingerlings can be cultivated in dedicated ponds or polycultured with cyprinid fish or prawns. For dedicated pond cultivation, 7000-10000 summer fingerlings are stocked per mu, combining fertilization and feeding commercial bait, with a daily feeding amount of 3%-5% of the total weight of fish in the pond. Commercial bait can be soybean cake, peanut cake, cornmeal, sweet potato flour, bran or artificial compound bait. In the same year, fingerlings of 12 cm in size can be reared.