Fig. 2. Mean wave amplitudes (± S.E.M.) for seven points along the body for four fish at three swimming speeds. The y axes show amplitude as a percentage of the total body length (L) and in cm. Black bars, 2.0 L s^-1 (absolute speed 46.5 cm s^-1), gray bars, 1.0 L s^-1 (absolute speed 23.3 cm s^-1) and white bars, 0.25 L s^-1 (absolute speed 5.8 cm s^-1). At the lowest speed, only the posterior 44% of the body undulates. As the swimming speed increases, a larger proportion of the body undulates and the body wave amplitude increases non-linearly. Note that over the speeds tested the tail-beat amplitude (determined by tracking point 7) does not plateau.