Hatchery production of spat
As in the case of oysters, mature scallops can be induced to spawn by thermal shock and larvae are grown in hatcheries by techniques similar to those for other bivalves. However, this method of seed production has not become very widespread because of the easy availability of natural seed. On the other hand, most of the seed used in culture of C. farreri and C.nobilis in China are reported to be hatchery-produced. In North America, too, the trend is to use hatchery-produced spat.
Sexually mature adults can be induced to spawn by increases in temperature and by the addition of milt from mature males in spawning tanks. Most species of scallop can be spawned by temperature shock, when properly conditioned brood stock are used. The bay scallop, A. irradians, the Chilean scallop, A. purpuratus, the deep sea scallop, P. yessoensis, andthe Chinese scallops mentioned above have all been spawned in hatcheries by this method. Other stimuli which can be used are ultra-violet rays and hydrogen peroxide in very low concentrations.
Scallops show high fecundity, for example a fully mature P. yessoensis can produce at least
100 million eggs. In spawning hermaphrodite individuals, care has to be taken to avoid polyspermy by collecting the sperm and eggs in separate containers and then artificially fertilizing the eggs. Fertilization can be achieved by adding 2–6ml sperm suspension for every litre of egg suspension. Embryonic development is rapid and free-swimming trochophores can be obtained in 8–24 hours, depending on water temperature. The optimum temperature for the development of the bay scallop is reported to be 26–28°C and gentle aeration and frequent water exchange are usually maintained in the tanks. The larvae are fed on phytoplanktonic organisms such as Monochrysis, Chaetoceros,Isochrysis, Phaeodactylum, Dunaliella and Tetraselmis. The larvae normally settle withintwo weeks.
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