Fig. 9. (A) The orientation of the pectoral fin showing the leading and distal edges and the z=1.5 cm plane, for which the in-plane velocity components (cm s^-1) are shown. The swimming velocity of the fish (45 cm s^-1) is subtracted from the x component of the velocity to reveal the vortical structures. (B) Two counter-rotating vortices are observed at t-0.906 s, just after stroke reversal. These are shed from the distal edge on the previous upstroke. (C) A large vortex spans the entire chord at t=1.065 s, when the thrust is minimum. (D) A vortex is shed from the trailing edge midway during the upstroke, t=1.14 s, leading to a momentary increase in lift force. (E) At t=1.167 s, 68% upstroke, the TEV is convected downstream. (F) At t=1.197 s, prior to stroke reversal, two vortices are shed from the distal edge. UDEV, upper distal edge vortex; LDEV, lower distal edge vortex; LEV, leading edge vortex; TEV, trailing edge vortex.