Fig. 1. Kinematics of (A) alternating and (B) synchronous pectoral fin propulsion in ventral view during steady swimming in the blue damselfish Pomacentrus pavo. (A) At 2 BL s^-1, the fish swims by alternating its pectoral fins at approximately 180° out of phase from one another. At 0 ms the left (upper) pectoral fin is protracted (abducted) and at 17 ms the left is retracted (adducted) while the right (lower) fin begins protraction. At 50 ms the left fin is seen during protraction and right during retraction. (B) At higher speeds (7 BL s^-1), damselfish switch gaits to an in phase fin beat pattern with simultaneous protraction (frame 17 ms and 67 ms) and retraction (0 and 50 ms). At 33 ms the fins are shown in mid-retraction phase.