Do the Fish Like the Flow Pattern in the Vertical Slot Fishway?

The flow patterns are different due to the varied fishway structures, and they can greatly affect the fish pass efficient of the whole fishway. In this study, we designed an experiment to contrast the fish responses to different flow patterns. Two distinct flow patterns were observed, depending on shape ratios of the pool’s lateral baffle length (P) to pool’s width (B). For P/B=0.1, flow pattern 1 (FP1), the principal flow along the side wall with almost no curve to the next slot, the recirculation region located between the long baffles occupies almost the whole pool. For P/B=0.25, flow pattern 2 (FP2), the principal flow leaving the slot enters the pools as a curved jet which disperses into the pool center before converging again towards the next slot, two eddy areas are formed on the both side of the principal flow. Fish behaviors in the two flow patterns were recorded by videos, the successful passing rate, the migration routes, and the migration time were analyzed. An analysis of the behaviour of juvenile grass carp (Ctenopharyngodon idella) in the scale model clearly showed that: the fish tend to spend more time to pass FP1 than FP2, and the migration rate of FP1 are much lower than FP2. The migration routes of the two flow patterns are obviously different, as the migration routes in FP1 are short but account a relatively higher velocity than the routes in the FP2. Through the above judgment, we can give a suggestion that FP2 tend to be more efficiency than FP1 in the vertical slot fishways.