How to ensure success in the three key areas when inducing spawning in broodstock in summer?

From the Start of Summer to Grain Full is the best period for inducing spawning in broodstock. At this time the water temperature is suitable, the spawning rate and hatching rate of broodstock are high, and the survival rate of fry after being stocked in ponds is also high. If this favorable opportunity is seized and strict control is exercised over the three key areas - broodstock selection, drug use, and spawning induction management - spawning induction can be successful.

Selecting good mature broodstock Whether the broodstock used for spawning induction are mature determines the quality of the spawning induction results. When selecting broodstock, maturity is generally judged by external characteristics. Mature female broodstock have a distended, rounded, soft and elastic abdomen; in grass carp and silver carp, the ribs can be felt when touched with a finger, and the genital pore protrudes and is slightly red. Immature female broodstock have a relatively rounded front abdomen but a thinner rear abdomen, are not soft enough and lack elasticity, and the genital pore does not protrude or protrudes only slightly and shows no red color. Overmature female broodstock show an excessively distended abdomen that has elasticity but no resilience, like an inflated appearance, and the genital pore protrudes and is congested and purplish red. Therefore, when selecting broodstock, maturity cannot be determined by abdominal size alone.

When selecting male broodstock, the fish body should be turned belly upward and the sides of the rear abdomen gently squeezed; those from which thick milky-white milt flows out and disperses immediately upon contact with water are good. Male broodstock with a small amount of milt or milt that forms strands and does not disperse quickly after entering water are immature; those with thin, watery, slightly yellow milt are overmature. During spawning induction, the ratio of female to male broodstock is 1:1.5, and their individual sizes should not differ too greatly. After selecting the broodstock, use a pencil, ballpoint pen, or smooth bamboo slip to number them in sequence on top of the head, put them into broodstock bags, weigh them, and keep records, ready for injection of spawning induction drugs.

Correct use of spawning induction drugs Commonly used spawning induction drugs include carp pituitary, human chorionic gonadotropin, ovulation-stimulating hormone and its analogs, mixed hormones, and others. Because the chemical composition of each drug is different and the mechanism of action is not the same, the fish species for which they are used in spawning induction are also not entirely the same. Generally speaking, carp pituitary can be used for various fish, ovulation-stimulating hormone and its analogs are often used to induce spawning in grass carp and black carp, mixed hormones are mainly used to induce spawning in bighead carp and silver carp, and human chorionic gonadotropin is more effective when mixed with other drugs and is ineffective when used alone to induce spawning in grass carp. The doses commonly used in production are determined by the dose injected per kilogram of female broodstock, generally 4-6 mg of carp pituitary, 1 international unit of mixed hormones, 800-1200 international units of human chorionic gonadotropin, and 20-80 micrograms of ovulation-stimulating hormone and its analogs. In the early stage of spawning induction or when inducing spawning in broodstock that have spawned before, the higher limit of the dosage is used; otherwise it should be reduced. The dosage for grass carp and silver carp is less than that for black carp and bighead carp. The dosage for male fish is 1/2 of that for female fish. The pectoral fin injection method is generally used; some are given a single injection, and some are given two injections. A single injection is generally carried out in the afternoon, and eggs are collected the next morning. For two injections, the first is generally given at around 10 a.m., injecting 1/10 to 1/8 of the total dose; the second is given in the evening, with a dose of 7/8 to 9/10 of the total dose, with the two injections 6-12 hours apart. When giving the second injection to the female fish, the entire dosage for the male fish is injected into its body at one time.

Strengthen spawning induction management After the injected broodstock are placed in the spawning pond, a designated person should watch over them to prevent the broodstock from jumping out, and attention should be paid to the activity of the broodstock, with records kept. In addition, after the second injection, water should be flushed once, and again before the broodstock become excited and spawn, each time for about 30 minutes, to give the fish the stimulus of flowing water and enhance their spawning rate.