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It is important to keep suitable area by boulder for fish in pool-and-weir fishway to make the migration rates high. In this study, migrating behaviors of oikawa by putting boulder on pool bed in pool-and-weir fishway was investigated. The migration rate of oikawa was obtained with the aid of two sets of digital video cameras. In addition, swimming position, swimming direction and migration route was investigated. It was found that migrating behaviors are difference between bed with boulder and flat bed. This is because oikawa swim slow flow area caused by boulder on pool bed. Further, swimming direction of oikawa in the case of flat bed comparatively match with each other, whereas that of it in the case of bed with boulder don't match.