How fish larvae swim: lessons from bending moment patterns

How sh larvae swim: lessons from bending moment patterns. Cees J. Voesenek, Gen Li, Florian T. Muijres and Johan L. van Leeuwen. Most species of sh swim with body undulations, also in their larval stages.These undulations result from uid-structure interaction between the internal tissues of the sh and the surrounding water. Although the governing physics Schoorl meeting 23-24 May 2019 19are complex, just-hatched larvae can already swim effectively, despite their presumably limited neural capacity for muscle control and lack of swimming experience. To examine how these larvae swim, we calculated spatio temporal distributions of the net bending moment along the body of free-swimming zebras larvae from 312 dpf. These distributions were computed from a large data setof video-tracked 3D motion, applying 3D computational uid dynamics, and a large-amplitude deformation model of the body. We show that bending moment patterns of each half-beat are similar throughout larval development, and across their typical swimming repertoire. The pattern changes mainly in amplitude and duration, depending on the combination of swimming speed and acceleration:combinations with high amplitudes and/or short durations support swimming at high speeds, or with strong accelerations. Although the patterns are similar,the envelope of possible amplitudes increases considerably in the rst days of development, allowing older larvae to swim at higher speeds and accelerations.The similarity of the bending moment patterns suggests that muscle activation patterns are also comparable. This may imply that sh larvae actuate their swimming relatively simply, despite the complex physics.