Prey availability and daily growth rate of juvenile Japanese flounder Paralichthys olivaceus at a sandy beach in the central Seto Inland Sea, Japan

摘要

The aim of this study was to characterize a nursery ground (Ohama Beach, Hiuchi-nada) for the Japanese flounder Paralichthys olivaceus in the central Seto Inland Sea having insufficient availability of mysids, Nipponomysis ornata and Iiella oshimai. We examined daily growth rates of wild juveniles; this measure can be used as an index of quality of a nursery. Juveniles consumed not only mysids, but also Crangon uritai and fishes. Mysid availability was lower at the study beach than in the nursery in the Sea of Japan; however, mean growth rates (MGRs) from May to June varied from 0.75 to 1.84 mm day(-1) and equaled that in the nursery with sufficient availability of mysids in the Sea of Japan. Prey availability was high from May to June and decreased after July. Additionally, water temperatures after late July were higher than the optimal temperature. Multiple regression analysis suggested that the low availability of prey and high water temperatures reduced the MGR after July. The results indicate that the optimal season for releasing hatcheryreared juveniles is from May to June, a period characterized by high availability of prey.