FUNCTIONS OF GRAZING FISHES OF AYU, Plecoglossus altivelis, AND PALE CHUB, Zacco platypus, ON THE COMPOSITION OF PERIPHYTON

Abstract

This study aims to propose a new approach of river flow management to sustain healthy riverbed condition by utilizing the grazing effects of freshwater fauna. We performed experiment to investigate the functions of grazing of ayu (Plecoglossus altivelis) and pale chub (Zacco platypus) on the composition of periphyton. The results of this study are as follows: i) The grazing of ayu restrains and reduces deposition of fine sediment and blooming of filamentous green algae, which were pointed out the inferior quality of riverbed condition. However, the grazing of pale chub cannot reduce them. ii) Feeding activities by not only ayu (Plecoglossus altivelis) but also pale chub (Zacco platypus) contributed to a decrease in the Autotrophic Index and an increase in the AFDM (%) and the ratio of living algae for the periphyton assemblages which were dominated by diatom.