Meeting Abstract

69.9  Jan. 7  Fin Shape and Fast Starts: A 3-D Kinematic Analysis. CHADWELL, B.A.*; STANDEN, E.M.; LAUDER, G.V.; Wake Forest Univ.; Harvard Univ.; Harvard Univ. chadba1@wfu.edu

Fish fins act as control surfaces to enhance locomotion and/or provide stability. Studies of median fins during C-starts have shown that, like axial kinematics, timing and direction of fin movements during Stages 1 & 2 (S1 & S2) are stereotypical and coordinated. To determine whether fin movement and shape during escape responses are due to passive deformation or active control, we compared fin kinematics to local axial kinematics. Three high-speed cameras were used to film fast starts in bluegill sunfish. Videos were taken at 500 fps and digitized to determine 3D kinematics of soft dorsal (sfD) and anal (An) fins. At five points along the length of each ray, lateral displacement (LD) and total curvature were calculated and compared to local axial kinematics, i.e. where the ray joins the midline. Throughout the entire fast start, the proximal regions of the rays matched, or even preceded, the timing, direction and speed of local axial movement, which was not expected if fin movements were completely passive. For more distal regions, ray kinematics differed from axial movement with these differences peaking at periods of high lateral acceleration: the onset of S1 when axial LD was first initiated, and then during the S1/S2 transition when axial LD changed directions. During these periods, the rays underwent the greatest amount of deformation; forming a brief S-curve with a proximal bend contralateral to the direction of axial LD and a distal ipsilateral bend. After the S1/S2 transition, differences between axial and distal fin kinematics decreased and fin deformation was reduced. We suggest that 1) sfD and An fins actively resist/reduce deformation throughout C-starts and 2) resistance to deformation of the distal fin regions is most effective when lateral acceleration is minimal.