CHADWELL, BA**; STANDEN, EM; LAUDER, GV; Wake Forest University; Harvard University; Harvard University: Dorsal and anal fin function during the C-start escape response in bluegill sunfish.

Axial kinematics during the fish C-start have been studied extensively and the pattern of body and caudal fin movement is well understood. However, there are effectively no detailed kinematic data on median fins such as the dorsal and anal fins during C-starts. We filmed the escape response of bluegill sunfish simultaneously with three high-speed, high-resolution cameras at 500 fps for a 3-dimensional kinematic study of median fins, in particular the soft dorsal (sfD) & anal (An) fins. Individual fin rays in the sfD & An fins were digitized to determine detailed movements in relation to the body and to each other throughout the escape maneuver. We also measured the degree of elevation & curvature of the rays. Fin movement occurred simultaneously with onset of Stage 1 (S1), increasing fin surface area by the elevation of anterior rays and depression of posterior rays. During S1, trailing edges of both fins were displaced from the midline contralateral to the direction of movement. Curvature of the trailing edges increased rapidly and maximum curvature occurred within 15-21 msec, just prior to maximum lateral displacement of the tail. At the start of the return stroke, i.e. Stage 2 (S2), the trailing edges were again displaced to the contralateral side and maximum curvature occurred within 2-4 msec. Unlike S1, fin curvature & displacement remained fairly consistent throughout S2 and maximum curvature & displacement were less. While fin kinematics differed between S1 and S2, the sfD & An fins showed coordinated movements and curvature throughout the maneuver. We suggest that the synchronicity of sfD & An fin kinematics functions 1) to resist rolling during the escape maneuver and 2) to possibly increase acceleration performance over that obtainable with collapsed median fins.