STARVATION OF DRIFTING GOBY LARVAE DUE TO RETENTION OF FREE EMBRYOS IN UPSTREAM REACHES

The embryonic drift pattern of amphidromous Rhinogobius species varies along river courses. It peaks soon after sunset in reaches with gentl e gradient on the plains, whereas it occurs throughout the day in stee p reaches. Examination of the size of the sagittal otolith and notocho rd length indicated that the age of embryos drifting in steep reaches varied widely, ranging from 0 to 7 days. Many had exhausted their yolk . We attributed the all-day drift in steep reaches to retention of dri fting embryos in slack waters or eddies near the banks. In contrast, m ost embryos drifting in reaches with gentle gradients were recently-ha tched individuals. We estimated that in normal or low river flow most embryos from the upstream reaches perish through starvation before the y reach the sea.