Feeding habits of Japanese temperate bass and copepod community in the chikugo river estuary, ariake sea, Japan

Abstract

The early life history of the Japanese temperate bass Lateolabrax japonicus in the Chikugo River estuary is characterized by a habitat shift toward lower salinity environments with larval growth. To clarify the ecological background of this ascending migration, feeding habits of the bass and distribution of prey copepods were investigated in March and April of 1997. Dominant copepods present in the environment and those preyed on by fish varied greatly with the salinity of the water. The bass preyed exclusively on cyclopoid copepods (mainly Cyclops vicinus) in the fresh-water region, and on a brackish-water calanoid Sinocalanus sinensis in the region of low salinities (0.1 to ca. 15). In the areas of salinities higher than 13.8, it preyed on common coastal copepods (Oithona davisae, Paracalanus parvus s.1. etc.). Surveys on zooplankton distribution revealed that S. sinensis was extremely abundant in the low salinity region, while the copepod density was much lower in high salinity and fresh-water regions, in spring. We concluded that the utilization of S. sinensis is one of the ecological key factors directly involved in the growth and survival of the Japanese temperate bass larvae and early juveniles which migrate toward the low salinity zone of the Chikugo River estuary.