1.Parent mussel selection

(1) Parent mussels require that their shells should be bright, bluish-blue, complete and intact, with a round "belly", a strong and plump body and a strong shell-closing force. The age of mussels should be 6-8 winter, and it is best for females to give birth to females.

(2) It is difficult to distinguish the sex of pearl mussel from the appearance, and it must be judged accurately according to the density and number of internal gill filaments. Generally, female mussels are slightly larger, with wider growth ring lines and slightly wider and thicker shells. When the mussel is opened, the gill filaments of the female mussel are arranged closely. After sexual maturity, the number of gill filaments in the outer gill flap reaches100 ~120; The arrangement of gill filaments in male mussels is sparse. After sexual maturity, the number of gill filaments in the outer gill flap is only 60 ~ 80.

2. Cultivation of parent mussels. The area of the parent mussel cultivation pond is preferably more than 2,000 square meters, the water depth is 1.5 meters, and the mud thickness at the bottom of the pond is moderate. The oxygen content of aquaculture water layer is 4.0 ~ 8.0 mg/L, the pH is 6.5 ~ 8.0, and the biomass of bait is10 ~ 20 mg/L. The water quality should not be too fat, so as to avoid the female germ cells from hypoplasia or sexual reversal due to hypoxia. If the parent mussel is cultivated in a small area of water, it must have slow flow conditions.

Generally, the ratio of male to female is 2∶ 1 (that is, 2 males 1 females 1 combination), and they are hung in the water layer end to end for sex ratio combination culture.

The cultivation of parent mussels should start in autumn, and the pond water should be injected and drained regularly, and the bait organisms should be propagated in time to promote the development and maturity of the gonads of parent mussels.

Second, fertilization and embryo development

1.Fertilization

(1) Hyriopsis cumingii is taken as an example in the fertilization season. In general, Hyriopsis cumingii has the ability to reproduce when it is 3 years old. Sexual maturity begins in May every year. At sexual maturity, the gonads of female Hyriopsis cumingii are orange in appearance, while those of male Hyriopsis cumingii are white. The spawning season is from May to July. Mature eggs are spherical; Mature sperm can swim with tail wagging under microscope. When most eggs in the reproductive nest are mature, the female mussels ovulate and fertilize. Hyriopsis cumingii lays eggs 5-8 times a year, with an amount of 400,000-500,000 eggs.

(2) Fertilization methods There are two fertilization methods: natural fertilization and induced fertilization.

① Natural fertilization: in the breeding season of mussels, the mature eggs of female mussels are discharged into the outer cavity of the body through the reproductive hole; The mature sperm of male mussel is discharged from the vas deferens to the suprabranchial cavity through the reproductive orifice, and then discharged into the external water body through the water outlet pipe. Sperm enters the female shell cavity with water and combines with the eggs to be pregnant, thus completing fertilization. The fertilized egg develops on the left and right external gill flaps of the mother clam.

② Induced insemination: The germ cells of male mussels usually mature earlier than those of female mussels. When some eggs of female mussels mature, the male mussel semen can be taken out manually, diluted with reproductive saline and injected into the mantle of female mussels, and the female mussels can be placed in a fertilization basin with a water temperature 3 ~ 5℃ higher than that of the original pool in advance for induced insemination. The sperm injected at 1 time only plays the role of inducing female mussels to ovulate, so it is necessary to inject the second diluted semen in the same way, and the sperm in this semen is just fertilized with the induced mature eggs. By inducing insemination, mussels can enter the breeding season in advance.

2. Embryonic development The fertilized egg undergoes the embryonic development process from fertilized egg → mulberry stage → blastocyst stage → gastrula stage → hookworm, forming hookworm. The whole embryonic development process usually takes 35 ~ 50 days.

Third, collecting hookworm larvae

After the metacercaria develops and matures on the outer gill flap of the mother mussel, it has sufficient silk and hooks, which can parasitize the fish and must parasitize the fish to complete the metamorphosis and become a young mussel. Therefore, when the hookworm is about to come out of the membrane, it is necessary to use the fish as a "seedling picker" to collect the hookworm on the fish.

1.Selection of fish for picking seedlings Silver carp, bighead carp, grass carp and common carp can all collect hookworm larvae, but the docile bighead carp and grass carp are the best. Each mussel needs 300 ~ 500 9.9 cm fingerlings for each seedling collection. Only by selecting excellent fish species with healthy constitution can we tolerate the parasitism of more hookworm worms.

2. Identification of the maturity of hookworm. Immature hookworm has no parasitic ability, so the maturity of hookworm must be identified. The identification method is to take out several cultured female mussels, first open the mussels with a shell opener, fix them to a certain extent with plugs, and then pick out a few hookworm larvae in the middle of the gills of mussels with a probe. If the picked hookworm larvae can adhere to each other into a chain, they are mature hookworm larvae.

3. Seedling picking method

(1) Collect seedlings indoors, inject clean fresh water with a depth of10 ~15cm into the basin, place the tested mother mussels on the bottom of the basin, then put the fish for collecting seedlings, and introduce a water pipe to make the water into running water. After several hours, it can stimulate the mother mussels to discharge hookworm.

(2) Outdoor seedling collection In the fresh water quality of rivers and lakes, you can use fish boxes to collect seedlings. A large number of seedlings are picked, which is suitable for mass production. When picking seedlings, it is necessary to change the picking points in time, and it is advisable to parasitize about 200 hookworm larvae per fish. If the number is too large, the fish picking seedlings will die. Before picking seedlings 1 day, it is necessary to pull the net to strengthen the physique of the fish, and discharge feces to avoid the pollution of hookworm larvae by the fish.