Movie 1

Vortex ring perturbation applied to the caudal fin of a Bluegill Sunfish during natural swimming
Vortex ring generated and used as a perturbation to the caudal fin of a Bluegill Sunfish (165 mm total body length) at three different swimming speeds, 0.65, 1.1 and 1.5 body lengths per second, during natural swimming. The video was recorded at 1000 frames per second and is being played at 0.04x speed. Particle image velocimetry was used to visualize the flow during the vortex formation and vortex's interaction with the fish fin.