Fig. 3. Views in the horizontal (XZ) plane of the wake of a Scomber
japonicus, 24 cm in fork length, swimming steadily at 1.2
FLs-1, where FL is fork length. Flow velocity is
represented by black vectors plotted over a color background indicating
vorticity. (A) Only low levels of vorticity (green) are present in the
horizontal plane of fluid just above the caudal fin, as seen when the dorsal
tip of the tail just intersects the sheet (indicated by the schematic view of
the caudal fin relative to the light sheet to the left of each plot).
Relatively strong negative and positive vorticity, associated with
counterclockwise and clockwise vortices, respectively, and a broad central jet
of flow are seen when the middle of the tail's upper lobe intersects the light
sheet (B) and when the light sheet is at the lateral midline of the tail (C).
One vortex ring is shed during each stroke of the caudal fin.
