Nakamura pointed out that the notch should be placed on one-side compared with alternate to shorten the amount of staying time of fish in a pool. However, there is little information on the suitable orifice location for shorten the amount of staying time of fish in a pool. In this study, orifice location in a pool-and-weir fishway is changed alternate or one-side. Behaviors of ayu, Plecoglossus altivelis altivelis, were obtained with the aid of two sets of digital video cameras. It was found that when orifice location is one-side, the consecutive migration rate becomes high and the amount of staying time of fish in a pool becomes shorten, as compared with those of alternate orifice.
