Fig. 3. Tips of the caudal, dorsal and anal fins cup actively into the flow. Motion of fins through half a tail beat from left to right in two transverse planes is presented. Each panel shows 7 tracings of the posterior margins of the fins, spaced equally in time, as seen from behind the fish. Color and thickness of the bar indicate lateral velocity of a particular segment of the fin. The beat frequency for each fin is the same, 4.9±0.3 Hz. (A) Caudal fin kinematics. Note how the upper and lower lobes bend into the flow at stroke reversal. Inset shows position of the two planes. (B) Dorsal and anal fin kinematics. Note the cupping motion of the outer edges of each fin. Scale bars are the same for A and B.