Fishway is important structure to expedite the migration of fish. It is necessary to grasp the influence that the conditions of the fishway give on swimming characteristics of the fish in designing the fishway. Therefore, it is necessary to examine the fishway of various shapes. However, the examination that changed a spanwise gradient at the bottom of fishway is not yet carried out. In this study, an investigation on swimming characteristics of Candidia temminckii was conducted under the condition that spanwise gradient at the bottom of open-channel and also the flow velocity are changed. It was found that the number of fish that swims at the deepest area in open-channel increases with the increase of the spanwise gradient at the bottom of open-channel. The fish in the case open-channel with the spanwise gradient at bottom is more stagnant than the case open-channel with the flat bottom.