Fig. 2. Motion of the pectoral fin in a bluegill sunfish (17 cm total length, L) during steady locomotion at 0.5 L s^–1. Each row shows frames from simultaneous lateral, ventral and posterior digital videos (taken at 250 Hz) at three time intervals, 97 ms (A), 142 ms (B) and 174 ms (C), during a single pectoral fin beat. Yellow arrows indicate the major fin motions (smaller amplitude movements of the fin surface are not labeled with yellow arrows), the small red and blue arrows show the position of the upper (dorsal) and lower (ventral) pectoral fin edges respectively, and the green arrow shows the location of the `dimple' on the dorsal fin margin that forms as a wave of bending passes out along the fin from base to tip. The large blue arrows and dot in A show the direction of water flow, which is perpendicular to the page in the posterior view. Note the considerable twisting and bending of the fin, and the cupped shape as the upper and lower fin margins move away from the body at the same time (A: posterior view). The fin beat begins at time 0 ms. Scale bars, 1.0 cm.