Fig. 3. Flow field adjacent to an eel (body length L=0.079 m) swimming steadily at speed U=0.121 m s^-1 from the lower right to the upper left of the field of view (sequence 1, see Table 1). The black arrows indicate the flow velocity. Blue shades indicate clockwise vorticity, red shades indicate counterclockwise vorticity. Darker shades indicate higher levels of vorticity. The flow fields are continued in Fig. 6. The time t is arbitrarily set to t=0 s for the first frame shown in Fig. 3. The field of view is 108 mmx108 mm.