1Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8528, 2National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, Hatsukaichi, Hiroshima 739-0452, Japan
Field experiments were done to evaluate the effect of predation of fishes on the oyster spats Crassostrea gigas suspended under oyster rafts in Hiroshima Bay. The oyster occurred throughout the year and the blue mussel Mytilus galloprovincialis was mainly observed in summer in the gut content of the black sea bream, Acanthopagrus schlegelii, and the finepatterned puffer Takifugu poecilonotus which seem to be the main predators around the oyster rafts. Spearman's rank correlation coefficient between relative amounts of epibenthic organisms and those of food items in the gut content of both fishes showed a significant correlation in summer. Cage experiments with different mesh sizes suggested that the number of oysters was decreased by the black sea bream from summer to autumn and by the finepatterned puffer in winter.