KINEMATICS OF PECTORAL FIN LOCOMOTION IN THE BLUEGILL SUNFISH LEPOMIS-MACROCHIRUS

The pectoral fins of ray-finned fishes are flexible and capable of com plex movements, and yet little is known about the pattern of fin defor mation during locomotion. For the most part, pectoral fins have been m odeled as rigid plates. In order to examine the movements of different portions of pectoral fins, we quantified the kinematics of pectoral f in locomotion in the bluegill sunfish Lepomis macrochirus using severa l points on the distal fin edge and examined the effects of swimming s peed on fin movements. We simultaneously videotaped the ventral and la teral views of pectoral fins of four fish swimming in a flow tank at f ive speeds ranging from 0.3 to 1.1 total lengths s(-1). Four markers, placed on the distal edge of the fin, facilitated field-by-field analy sis of kinematics. We used analyses of variance to test for significan t variation with speed and among the different marker positions. Fin b eat frequency increased significantly from 1.2 to 2.1 Hz as swimming s peed increased from 0.3 to 1.0 total lengths s(-1). Maximal velocities of movement for the tip of the fin during abduction and adduction gen erally increased significantly with increased swimming speed. The rati o of maximal speed of fin retraction to swimming speed declined steadi ly from 2.75 to 1.00 as swimming speed increased. Rather than the enti re distal edge of the fin always moving synchronously, markers had pha se lags as large as 32 degrees with respect to the dorsal edge of the fin. The more ventral and proximal portions of the fin edge usually ha d smaller amplitudes of movement than did the more dorsal and distal l ocations. With increased swimming speed, the amplitudes of the lateral and longitudinal fin movements generally decreased. We used two dista l markers and one basal reference point to determine the orientation o f various planar fin elements. During early adduction and most of abdu ction, these planar fin elements usually had positive angles of attack . Because of fin rotation, angles of attack calculated from three-dime nsional data differed considerably from those estimated from a simple lateral projection. As swimming speed increased, the angles of attack of the planar fin elements with respect to the overall direction of sw imming approached zero. The oscillatory movements of the pectoral fins of bluegill suggest that both lift- and drag-based propulsive mechani sms are used to generate forward thrust. In addition, the reduced freq uency parameter calculated for the pectoral fin of Lepomis (sigma=0.85 ) and the Reynolds number of 5x10(3) indicate that acceleration reacti on forces may contribute significantly to thrust production and to the total force balance on the fin.