| The boulders on Ramp fish passage create turbulence and backwater, and decrease the flow velocity on the slope. To consider adequate boulder arrangement and size, the swimming physiology of chars and freshwater sculpins on a ramp fish passage were observed using ultra-high speed cameras. Each species required different boulder arrangements based on their swimming physiology. Chars, which have large swimming forces, used the straight flow along the boundary current for swimming and the low velocity areas at the rears of boulders to rest for short periods. In the high velocity flow against their swimming force, they migrated above the rough sides of boulders. In both cases, the fine spaces between boulders that matched their body lengths were required to maintain balance in high flow velocities. Sculpins, which are bottom swimming fish, have weak swimming forces. They lose their swimming balance and fail to migrate in boundary flow currents and in the turbulent water around boulders. They avoid unstable flow based on its direction or its velocity. High density and several linear arrangements of boulders are required for these bottom-swimming fish. |
