Artificial breeding technology for bay scallop farming
Indoor artificial breeding of the bay scallop includes the following procedures: Parent scallop selection and fattening. The parent bay scallops selected generally have a shell height above 5 cm and are required to have full gonadal development; if they have not reached mature fullness, they are temporarily cultured for fattening. The feed types for parent scallop fattening are generally Platymonas, Nitzschia closterium, Chaetoceros, golden algae, etc., and formulated feed can also be used. In the 1980s, China could already carry out artificial temperature-controlled breeding of the bay scallop. Under temperature control, parent scallops are stocked and fattened in advance, thereby obtaining juvenile scallops earlier and extending the growth cycle in farming. The bay scallop is generally kept at a controlled temperature of 20-24 degrees Celsius. The daily water temperature increase is 1-2 degrees Celsius. The daily feeding amount is: Platymonas 60,000-100,000 cells/ml; diatoms and golden algae 150,000-400,000 cells/ml. During fattening, other suitable physicochemical factors are: pH 7.9-8.2; salinity 25‰-28‰; total ammoniacal oxygen not exceeding 300 mg/cubic m; light not greater than 500 lux; chemical oxygen demand not higher than 2.3 ml/L. After 20-25 days of stocking, mature sperm and eggs can be obtained.
Fertilization and hatching. Scallop sperm and eggs are stirred in purified seawater for fertilization and hatching. The development processes of the fertilized eggs and larvae of various scallops are basically similar, with slight differences in development time. The fertilized egg passes through the multicellular stage, morula stage, blastula stage, and gastrula stage; larval development is divided into trochophore, straight-hinge larva, early umbo larva, late umbo larva, and after the eyespot appears, the eyespot larva stage; when the foot can crawl and the velum begins to degenerate and disappear, it enters the creeping stage, and after attachment and metamorphosis produce a secondary shell, it becomes a juvenile scallop.
Larval rearing. After hatching, the straight-hinge larvae are selected for quality and cultured in separate tanks at a density of 8-12 larvae per ml of water. Suitable environmental factors to be controlled during rearing: water temperature 22-24 degrees Celsius, ammonia not exceeding 200 mg/cubic m; light below 500 lux; continuous or intermittent aeration, dissolved oxygen not lower than 5 mg/L; pH 7.9-8.2; COD not higher than 2 mg/L. The initial feed is Phaeodactylum tricornutum, golden algae, and Chaetoceros. After 3 days, a mixed feed mainly of Platymonas is given. The feeding amount is determined by how much food is in the larval stomach. Water is changed twice a day, and the temperature difference during water change should not exceed 2 degrees Celsius. During larval rearing, to prevent water quality pollution and infection by microorganisms and bacteria, management work such as changing tanks 2-3 times and discharging sewage from the tank bottom should be carried out. When necessary, antibiotics or chelating agents are added to purify the water quality.
After the eyespot appears, attachment substrates should be placed in time. Intermediate rearing is carried out. Before leaving the tank, the temperature should be gradually lowered, by about 2 degrees Celsius per day, until it is close to the natural seawater temperature, and then it is transferred to the sea for temporary culture. Double mesh bags, plastic tubes, or net cages can be used for seedling preservation, and temporary culture for seedling preservation can also be done in large prawn culture ponds. After 25-30 days of intermediate rearing, when the shell height reaches 0.5 cm, they can be sold as commercial seedlings. By the late 1980s, China's artificial scallop breeding technology had reached an industrial level, with 100,000-500,000 commercial seedlings produced per cubic meter of water, and a maximum of 988,000.