Abstract: The response mechanism of fish swimming to the surrounding flow environment is important to ecological protection and bionic application of fishes. Using the high speed video experimental technology and ANSYS FLUENT numerical simulation software, we observed the kinematic behaviors of Carassius auratus swimming in the wake of a circle cylinder. Their movements in uniform flow were also studied using comparative analysis. By analyzing the variation of body profiles during fish swimming, the parameters such as the tail-beat frequency, head-swing angle, flapping amplitude, and wavelength and wave speed of the body deformation were measured. Their dependency on factors such as flow speed and flow structure was assessed. The results showed that the carps may exploit a Kármán gait to hold their stations in the Kármán vortex street. Whether they exploit this special gait or not was related to the intensity and shedding frequency of the vortices. During the Kármán gait, the carp synchronized its movement with the vortex street, with the flapping frequency equals to the vortices shedding frequency. Compared with that in a uniform flow with equivalent flow velocity, the head-swing angular and the flapping amplitude of the whole body were much larger, the tail-beat frequency was lower, and the wavelength and wave speed of the deformation of the fish were larger. Our results deepen our understanding of fish swimming mechanism and provide basic support for bionic application and ecological protection of fishes.

Key words: underground runoff and sediment yield, surface runoff and sediment yield, artificial rainfall, Karst slope cropland