Breeding techniques of clam

The clam is dioecious, and the reproductive gland is located around the dorsal intestine of the foot, showing a grape-like gland. the reproductive season is usually in summer, and the sperm and eggs are fertilized in the Gill cavity of the outer Gill until the hookworm larvae are formed. Due to the adhesion of the mother, the fertilized egg will not be washed out by the current, but will stay in the Gill cavity to develop, so the Gill cavity of the outer Gill is also called the parenting sac. Let's take a look at the breeding technology of the clam.

Selection and cultivation of parent clam

1. Parent clam selection

① parent mussel requires that the shell color should be bright, bluish blue, the shell is intact and intact, the "abdomen" is round, the mussel body is strong and fat, and the shell closing force is strong. The best clam age is 6-8 winter age, and the female clam should give birth to the female clam.

It is difficult to distinguish the sex of ② pearl mussel from its appearance, and it can only be judged accurately according to the density and root number of the inner Gill filaments. In general, the female clam is slightly larger, the growth ring is wider, and the shell is also slightly wider and thicker. When the mussel was opened, the Gill filaments of the female clam arranged closely. After sexual maturity, the number of the outer Gill filaments of the female clam reached 100-120, while that of the male clam was sparse. After sexual maturity, the number of Gill filaments of the outer Gill was only 60-80.

2. Parent clam cultivation: the area of parent clam cultivation pool should be more than 2000 square meters, the water depth is 1.5m, and the thickness of silt at the bottom of the pond is moderate. The oxygen content in aquaculture water layer is 4.0 ~ 8.0 mg / L, pH is 6.5 ~ 8.0 mg / L, and the feed biomass is 10 ~ 20 mg / L. The water quality should not be too fat, so as to avoid dysplasia or sexual reversal of female germ cells due to hypoxia. If the parent clam is cultivated in a small area of water, it must have the condition of slow flow.

3. The proportion of male and female: generally, the ratio of male and female is 2 ∶ 1 (that is, 2 male clip and 1 female is 1 combination), and the tail is suspended in the water layer to make progress than the combination culture. The cultivation of parent clam should begin in autumn, regular injection and drainage of pond water, timely breeding of food organisms, and promoting the development and maturity of the gonad of parent clam.

Fertilization and embryonic development

1. Fertilization season: take Hyriopsis cumingii as an example. In general, Hyriopsis cumingii has the ability to reproduce at the age of 3 years. Sexual maturity begins in May every year. At sexual maturity, the gonads of female Hyriopsis cumingii are orange, while those of male Hyriopsis cumingii are white. The spawning season is from May to July. The mature egg is spherical and the mature sperm can swing its tail under microscope. When most of the eggs in the reproductive nest mature, the female clam ovulates and fertilizes. Hyriopsis cumingii lays eggs 5-8 times a year, and the number of eggs laid is 400000-500000 eggs.

2. Fertilization methods: there are two methods of oyster fertilization: natural fertilization and induced fertilization.

① natural fertilization: in the breeding season, the mature eggs of the female clam are excreted into the mantle cavity through the reproductive pore, and the mature sperm of the male clam are excreted from the vas deferens to the suprabranchial cavity through the reproductive pore, and then into the water body in vitro through the outlet pipe. The spermatozoa enter the outer cavity of the female clam with water and combine with the eggs waiting for pregnancy to complete fertilization. The fertilized eggs undergo embryonic development on the outer Gill valves on the left and right sides of the female clam.

②-induced insemination: the germ cells of male clams usually mature earlier than female ones. When part of the eggs of the female clam matured, the semen of the male clam was artificially taken out, diluted with reproductive saline and injected into the outer membrane of the female clam, and the female clam was pre-placed in a fertilization basin where the water temperature was 3-5 ℃ higher than that of the original pool to induce fertilization. The semen injected for the first time can only induce the ovulation of the female clam, and the second diluted semen needs to be injected in the same way, and this time the sperm in the semen happens to be fertilized with the induced mature egg. Through induced insemination, mussel can enter the breeding season ahead of time.

3. Embryonic development: the fertilized egg starts from cleavage and goes through the embryonic development process of fertilized egg → morula stage → blastocyst stage → progut stage → hookworm. The whole process of embryonic development usually takes 35 to 50 days.

Harvest of cercariae vaccine

After the development and maturity of the cercariae on the outer Gill lobe of the female clam, it has foot filaments and hooks, which can parasitize the fish and must be parasitic on the fish in order to complete the metamorphosis process and become the young clam. Therefore, when the hook cercariae are about to come out of the membrane, the fish should be used as a "seedling collector" to collect the hook cercariae on the fish.

1. Selection of larvae: silver carp, bighead carp, grass carp and carp can all collect hook cercariae, but it is better to have gentle bighead carp and grass carp. Each clam needs 300 fish fry with a size of 9.9 cm each time. Good fish species with good physical health should be selected in order to tolerate the parasitism of more hookworm worms.

2. Maturity identification: immature hookworm cercariae do not have parasitic ability, so the maturity of hookworm cercariae must be identified. The identification method is to take out several cultivated female clams, first open the clam with a shell opener, plug and fix it to a certain extent, and then use a probe to pick out a few hookworm larvae in the middle of the clam's Gill valve. If the picked hookworm larvae can adhere to each other into a chain, it is a mature hookworm larva.

3. The method of collecting seedlings

① indoor seedling collection: inject 10-15cm clean fresh water into the basin, place the female clam at the bottom of the basin, then put it into the fry, and drain it into a water pipe to make the water flow. After a few hours, it can stimulate the mother clam to expel the cercariae.

② outdoor seedling collection: in the fresh water quality of rivers and lakes, fish box can be used to collect seedlings. The number of seedlings collected is large, so it is suitable for mass production. The seedling collection site should be changed in time, and it is appropriate for each fish to parasitize about 200 hookworm cercariae, which will lead to the death of seedling fish. One day before collecting seedlings, the fry should be trained by pulling net to strengthen their physique and discharge feces so as to avoid contamination of larvae.