Effective pretreatments of spat-collectors for induced settlement of the Pacific oyster, Crassostrea gigas

The erects of pretreatment of scallop shell spat-collectors on oyster Crassostrea gigas larval settlement were studied. Spat-collectors were pretreated by immersion in 1 mM L-DOPA, filtered seawater, surface seawater, filtered seawater with oyster shells or live adult oysters for 4 days. An average of 84% spats were found on spat-collectors pretreated in seawater with the presence of live adult oysters after 3 days of the settlement experiment. This settlement-inducing effect was increased by extending the pretreatment period and by increasing the number of adult oysters. The settlement-inducing effect decreased considerably when such pretreated spat-collectors were soaked in hot (50 degrees C) water and dried. The results of these experiments confirmed that the pretreatment with live adult oysters increased the ratio of larval settlement to spat-collectors, and enabled the setting period to be reduced. The pretreatment of spat-collectors with live adult oysters could be applied to the large-scale artificial setting of oyster larvae.