Fig. 8. Body contours over one tail-beat of (A) an eel and (B) a mullet swimming steadily at 1.4Ls^-1 (slip 0.6-0.7, where L is body length). The time between contours is 0.04 s. The light-shaded area indicates the initial water displacement by the head. The maximum crests (thick black line) of the body wave extend considerably beyond this initial displacement only in the eel (grey triangles). This means that only the eel generates strong high-pressure flows. The troughs (thick black line) recess significantly beyond the initial displacement of the head in both fish (grey triangles). This causes strong low-pressure flows in both species.