Fig. 4. DPIV analysis of the wake of the tail of a representative Triakis semifasciata (A) and Chiloscyllium punctatum (B) during steady horizontal locomotion. On the left is a tracing of the tail depicting its position relative to single the shed vortex ring visible in this vertical section of the wake. The color plot to the right shows fluid vorticity, with superimposed black velocity vectors representing the results of DPIV calculations based on particle displacements. A strong jet, indicated by the larger velocity vectors, passes between two counter-rotating vortices representing a slice through the vortex ring shed from the tail at the end of each beat. The white dashed line indicates the ring axis cycle. Note that a green color indicates no fluid rotation, a blue color reflects clockwise fluid rotation and a red/yellow color indicates counterclockwise fluid rotation. To assist in visualizing jet flow, a mean horizontal flow of U=19 and U=24 cm s^-1 was subtracted from each vector for T. semifasciata and C. punctatum, respectively.

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