Fig. 2. Experimental apparatus. (A) Fish swam in a multi-speed flow tank. Three high-speed digital cameras captured synchronous dorsal, ventral and lateral views of swimming fish. (B) Fin ray digitizing. Four points along every other fin ray, represented here as yellow (x) symbols and lines, were digitized in three dimensions using two simultaneous views (only the lateral view is shown here) to calculate fin area and fin ray curvature. Yellow dots represent the trailing edge of each fin as well as the body point that were digitized to calculate excursion and phase lag.