Meeting Abstract
The ability for fishes to move fast is critical for successful prey capture and predator evasion. Here, we uncover the physiological and hydrodynamic mechanisms of a previously undescribed method of propulsion which allows undulating fishes to double their maximal swimming speeds; they do this by superimposing a low-amplitude impulse wave onto their main undulatory wave. Analogous to constructive interference in physics, the impulse wave enhances the transfer of the body momentum to the wake by snapping the tail like a whip, propelling the fish forward in ways that would not be possible with classical undulatory movements. The superimposed impulse wave increases tail tip velocity independently without increasing the body wave speed. Our preliminary data (n=3 rainbow trout, L=22.4±2.0 cm) show that during whipping, an impulse wave is initiated in the region of the dorsal fin. Trout regulate timing and speed of the impulse wave in a way that increases the lateral amplitude of the tail tip excursion up to 20% compared to fish swimming steadily. This allows fish to increase tail tip velocity and angle of attack by 40% and 15°, respectively. Our results also show that a whipping fish generates optimal vortex rings with much higher circulation than those observed during undulation at a comparable speed. We hypothesize that during whipping fish separate muscle functions by coordinating undulatory and impulse waves independently. We predict that red muscles continue powering body undulations as in steady swimming, whereas a transient burst of local white muscle is responsible for the initiation and transmission of the impulse wave.
