STANDEN, E.M.*; LAUDER, G.V.; Harvard University; Harvard University: Hydrodynamics function of dorsal and anal fins in trout ( Salvelinus fontinalis)

Fish fins produce moments around the fish�s body that potentially contribute to thrust and stability. The dorsal and anal median fins are located above and below the rolling axis of the fish and oscillate during locomotion, which suggests they produce rolling moments on the fish�s body. How moments produced by dorsal and anal fins affect fish stability is not well understood. Previous flow visualization experiments have shown that the dorsal fin produces large lateral jets above the fish�s rolling axis possibly causing rolling instabilities during swimming. The location and structure of the anal fin suggests it may counteract the forces produced by the dorsal fin. To date, anal fin wake structure has not been described. In this study we use particle image velocimetry to visualize the wake structures of dorsal and anal fins of brook trout (Salvelinus fontinalis). Using two parallel light sheets with high-speed digital cameras filming each sheet simultaneously we assess the kinematics of the dorsal and anal fins as well as the timing, magnitude and direction of forces produced by these fins during swimming. We find that the anal fin is producing large lateral jets of similar magnitude and direction to the dorsal fin. We hypothesize the timing, direction and magnitude of dorsal fin jets are balanced by anal fin jets to minimize rolling perturbations experienced by fish.