Our previous research suggested that the entrance selection of a multiple path fishway affects migration success ratio. In this research, firstly, we prove that entrance selection affect migration success through field experiment. Secondly, we determine suitability index for air bubble condition, which were 0.27 for no bubble, 0.88 for surface bubble, 1.00 for bubble reaching mid-depth, 0.16 for bubble reaching the bottom. They are opposite results to the existing research. It seems that air bubble itself is not preferred but the cover created by air bubble is preferred. Thirdly, we conduct entrance selection experiments in the field, and found that the major mechanism of entrance selection was air-bubble, followed by velocity. Sound pressure and depth affected little.