Fig. 5. Comparison of theoretically predicted velocity profiles across planar sections of isolated vortex rings (left panels, where paired circles indicate vortex cores in solid-body rotation and arrows indicate the direction of induced flow rotation; Milne-Thompson, 1966) with velocity profiles taken from XY planar light-sheet images of the wake of a mackerel 26 cm (fork length, FL) swimming at 1.2 FL s^-1 (right panels). The velocity values shown are raw data calculated using a high-resolution 50x50 vector field. (A) X' is the longitudinal axis of the vortex ring, which traverses the centers of the two vortex cores; (B) Y' is the central axis of a vortex ring (perpendicular to X'); (C) Y' is the line extending across the counterclockwise vortex core parallel to the ring's central axis (see Fig. 4B for an illustration of axes used here on an XY planar vorticity plot). The components of velocity parallel to X' and Y' are u' and v', respectively. In the region of the central jet, v' is negative.