Fig. 2. Experimental approach for visualizing the median fin wake. (A) Within the region bound by the rectangle, lateral video images of bluegill sunfish were recorded during steady swimming at both low and high speed and during unsteady turning maneuvers. (B) Representative lateral-view reference image showing the dorsal lobe of the tail and the trailing edge of the soft dorsal fin intercepted by a horizontal (frontal-plane) laser sheet seen on edge as a white stripe. (C) Synchronized dorsal-view video of this laser sheet allowed analysis of wake flow using digital particle image velocimetry (see Materials and methods). (D) To study the wake structures and fluid forces generated by the soft dorsal and caudal fins, flow was analyzed within laser planes at three heights (1–3). Fin movements and the resulting fluid flow within these planes are illustrated in Figs3–8 and Fig.10.
