Physical origins of speed control in swimming fishes.

A physical model links fish swimming speed to body morphology and kinematics, showing maximum stride length depends on wavelength and phase offset, not body length.

• Why it matters: Understanding the physical basis of fish speed control addresses the lack of a comprehensive framework explaining the empirical linear relationship between tail-beat frequency and swimming speed across species.
• What they did: The authors derived a speed relationship from fin thrust and boundary layer drag, validated it against experimental data, simulations, and Bainbridge’s original measurements, covering diverse swimming regimes.
• The result: The model predicts swimming performance within ten percent without recalibration, revealing that body waveform, not actuation frequency, primarily determines speed, expanding the understanding of propulsion in fishes and bioinspired systems.