Abstract: Observation experiment on fish swimming in a self-circulating water tank was performed to investigate the movement patterns of Crucian in flow channels with different widths and inflow velocities. The Crucians for experiment were 18-20 cm in length and 180-200 g in weight. The width of the flow channel was set to 7-60 cm and the range of inflow velocity was 0.1-0.6 m/s successively. High-speed photography was employed to record the swimming process of Crucian under different flow conditions. And then Image Pro and other analysis software were used to quantify parameters such as tail-beat frequency, amplitude and wave number of fish body. The equations of fish motion under various experimental conditions and the variation law of each parameter along with the inflow velocity and channel width were obtained. Results revealed that the oscillation frequency, amplitude of oscillation and body wave number of Crucian changed apparently with the variation of inflow velocity, but not evidently with the variation of channel width. In general, the motion frequency, amplitude and body wave number increased along with the increasing of incoming flow velocity. Current researches of fish movement mostly focus on the influence of flow velocity on frequency and amplitude or turbulence rather than on the influence of flow path width. The present research offers some background information and theoretical basis for the future researches, design and bionics application of fishway.

Key words: motion pattern of fish swimming, flow path width, incoming flow velocity, tail-beat frequency, amplitude