1Usa Marine Biological Institute, Kochi University, Tosa, Kochi 781-1164, 2Nishinihon Institute of Technology, Wakamatsu, Kochi 780-0812, 3Kanefuku Co., Ltd., Higashi, Fukuoka 812-8654, 4Takahashi Research Office of Freshwater Biology, Yasu, Kochi 781-5603, Japan
The distribution and feeding habits of the larvae of ayu Plecoglossus altivelis altivelis were investigated in the coastal waters of Tosa Bay from 2000 to 2004. The larvae (chiefly yolk-sac and preflexion stages, 4.0-13.5 mm BL) were distributed horizontally 3 km inshore and vertically on the surface, being influenced by coastal waters. Average feeding incidences were 40.8-47.9% in yolk-sac and 46.6-81.5% in preflexion stages. They fed on cope-pods, chiefly Oithona and Paracalanus type, which were dominant in the zooplankton fauna of the waters. In accordance with the development of the larvae, the copepods consumed gradually changed from the nauplius to copepodite stage. When the monthly frequency of hatching of ayu larvae inhabiting surf zones close to the waters investigated were compared among year groups, it was suggested that the degree of assemblage of early larvae near the coast and the density of copepods were significant for their survival until migration to the surf zones.