1Fisheries and Ocean Technologies Research Center, Hiroshima Prefectural Technology Research Institute, Kure, Hiroshima 737-1207, 2Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8528, Japan
The presoaking of spat collectors in seawater containing adult Pacific oysters Crassostrea gigas is known to induce their larval settlement. In this study, we experimentally examined how presoaking conditions affect variations in success of larval oysters, using scallop Patinopecten yessoensis shell chips as spat collectors. The rate of larval settlement was enhanced by increase in water temperature, number of adult oysters, and length of presoaking period, while it was not affected by feeding to adult oysters. The ammonia-N concentration in the presoaked water was also closely related to the success of larval settlement. We herein propose a new indicator, termed condition index, which is the product, expressed in mg/L・hours, of the ammonia-N concentration multiplied by presoaked hours, and suggest that larval settlement is very successfully induced at about 20 mg/L・hours.