Fig. 4. (A) Mean propulsive wave speed for the lowest (white), middle (hatched), and highest (black) swimming speeds (mean ± S.E.M., N=16 cycles). Wave speed was determined by calculating the time required for a wave to travel past two points of a known distance. Note that the proportion of the body that undulates depends on the swimming speed. In each case, the body wave traveled posteriorly faster than the forward speed of the fish. (B) Changes in propulsive wave speed down the body were investigated for the two extreme swimming speeds. At 0.25 L s^-1, only a small region of the body undulates. When that region is divided in half, both the anterior (light gray column) and posterior (dark gray column) section contain part of the dorsal and anal fins. Wave speeds for the two segments are not significantly different (=0.05). (C) At 2.0 L s^-1, the entire body undulates except for the rigid neurocranium. Due to the presence of the median fins, the posterior section of the propulsive wave is significantly slower (P<0.001) than the anterior section, reflecting an overall deceleration of the body wave.

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