Longitudinal distribution and dietary habits of the genus Rhinogobius in the Genka River of northern Okinawa Island, Japan

Abstract

The longitudinal distribution and dietary habits of five and fbur Rhinogobius species were investigated in the Genka River of northern Okinawa Island, Japan. Two sampling points for the assessment of fbod habits, and locations for determining longitudinal distribution (n=13), were identified along the length of the Genka River. Habitat prefbrence was observed to be relatively discreet among the five Rhinogobius species sampled: R. giurinus was distributed from the tidally influenced river reaches to the lower river reaches, R. sp.MO was commonly fbund in the middle river reaches, R. sp.CB was fbund in riffles along the length of the river without the lowest and uppermost stations, R. sp.DA occurred from the middle to the uppermost river reaches, and R. sp .BB was commonly found in pools from the middle to the uppermost reaches of the Genka River. Four Rhinogobius species (MO, CB, DA, BB) were found to feed primarily on Trichoptera, with R. sp.CB and R. sp.BB also observed to feed on terrestrial insects. R. sp.DA observed to feed on molluscs (snails). These findings suggest that the members of Rhinogobius species assayed in the Genka River have become somewhat specialized with respect to habitat (5 species) and food prefbrence (4 species).