Experience in the sources and selection of broodstock for freshwater pomfret (pirapitinga) farming

Freshwater pomfret has a strong reproductive capacity. When selecting broodstock, choose individuals that are large, fast-growing, free of any disease or injury, with smooth body surface and clearly defined coloration. Also avoid using fish that are closely related as broodstock, so as to prevent degeneration of the offspring and its effect on growth.

(1) Sources of broodstock: Since the introduction of freshwater pomfret into China, the broodstock have mainly come from reserve broodstock selected and retained from pond culture, which are then reared to become mature broodstock for artificial propagation. To avoid "inbreeding" causing degeneration of the offspring, offspring produced by breeding farms in two or more regions can be selected and retained as reserve broodstock.

(2) Broodstock selection

① Male and female identification: During broodstock rearing and hormone-induced spawning, the appropriate ratio of females to males must be mastered, so the sex of the broodstock needs to be correctly identified. Like many vertebrates, when fish approach or reach sexual maturity, the gonads secrete a sex hormone whose physiological action produces secondary sexual characteristics, which are especially obvious on male fish. The secondary sexual characteristics of freshwater pomfret are never obvious throughout life, making male and female identification rather difficult. Even during the breeding season they are not easy to distinguish. In mature females, the outline of the ovary is visible on the abdomen, the rear abdomen is soft and elastic, and the genital pore and anus are slightly red and clearly protruding outward. In terms of body color, compared with males, the body color is darker, and the red color on the chest, pelvic fins and anal fin is deeper. The main characteristics of mature males are: the area from the front chest to the abdomen on the side of the body shows red, deeper and more vivid than in females; the body surface is silvery gray; the urogenital pore is slightly closed; the abdomen is relatively flat; and gently squeezing the abdomen causes a small amount of milt to flow out.

② Maturity age and body weight: Under normal conditions, the age and body weight of freshwater pomfret are positively correlated, that is, the older the age, the greater the body weight, and vice versa. For broodstock of the same age reared in different waters, differences in body weight may be quite due to different ecological and nutritional conditions. Freshwater pomfret reaches sexual maturity at age 3 or above, with body weight generally 2.5-4 kg for females and 2-3 kg for males, and body length over 40 cm. The broodstock selected must be fish with a strong physique, smooth body surface and no wounds, to be used as broodstock for induced spawning.

Because freshwater pomfret has a large spawning capacity and can spawn multiple times within a year, for an ordinary unit the number of broodstock need not be too large. As long as the broodstock are well reared and the spawning and fertilization rates are high, 30-50 pairs are sufficient.