ASCENDING SMALL GYMNOGOBIUS UROTAENIA SP. FISHES DURING THE UPSTREAM MIGRATION AT THE NOTCH OF STEPPED-POOL FISHWAY

Abstract

 In this research, the ascending of small Gymnogobius urotaenia sp. (Goby) fishes was studied, the flow velocity distribution around the notch was measured, and an observation survey was conducted using an underwater video camera at a full cross-sectional overflow stepped-pool fishway at the mouth of the Iwaki River in the first head works in the Aomori Prefecture. The results show that Goby fishes with a length under 5 cm was faced difficulty in swimming upstream at a hydraulic condition of approximately 30 cm of overflow water depth at a 40 cm thick notch without chamfer and a 20 cm head between pools. As Japan comprises numerous fishways of the same type, this study could contribute to knowledge about the hydraulic conditions which is hard to ascend for the Goby under 5 cm body length.