Abstract
In order to apply individual-based fish school behavior model to evaluate fishway effectiveness, parameters in the model e.g. parameter of rheotaxis should be improved. In this study, upstream behavior of Japanese dace school was observed in an experimental vertical-slot fishway installed in an indoor flume channel, and rheotaxis of individual fish was examined. In the upstream passage, fish school seldom entered the pools created between the vertical-slot baffles. Flow velocity was 0.2m/s at the no-baffle area in the flume channel. In contrast, water flow was accelerated at the slot area of vertical-slot fishway because the channel width was narrowed by the baffles, and the velocity was over 0.5m/s at the center of the slot area. However, there was a zone of low flow velocity (0.2m/s) close to the pools in the slot area, and fish school ascended at the low-velocity zone. When fish traversed fast flow area at the upper part of the slot area, the rheotaxis appeared to become strong. Fish employed the burst speed against fast flow, while they swam at their sustainable speed in ascending in the low-velocity area. In vertical-slot fishway, the flow velocity varied largely, and the flow pattern was complicated. Fish were likely to ascend through the low-velocity zone, and appeared to change their swimming speed according to the flow velocity to maintain the ground speed.
