title: Boxfish swimming paradox resolved: forces by the flow of water around the body promote manoeuvrability.
abstract: The shape of the carapace protecting the body of boxfishes has been attributed an important hydrodynamic role in drag reduction and in providing automatic, flow-direction realignment and is therefore used in bioinspired design of cars. However, tight swimming-course stabilization is paradoxical given the frequent, high-performance manoeuvring that boxfishes display in their spatially complex, coral reef territories. Here, by performing flow-tank measurements of hydrodynamic drag and yaw moments together with computational fluid dynamics simulations, we reverse several assumptions about the hydrodynamic role of the boxfish carapace. Firstly, despite serving as a model system in aerodynamic design, drag-reduction performance was relatively low compared with more generalized fish morphologies. Secondly, the current theory of course stabilization owing to flow over the boxfish carapace was rejected, as destabilizing moments were found consistently. This solves the boxfish swimming paradox: destabilizing moments enhance manoeuvrability, which is in accordance with the ecological demands for efficient turning and tilting.
authors.affiliation: Department of Biology, Universiteit Antwerpen, Universiteitsplein 1, 2610 Antwerpen, Belgium Evolutionar Morphology of Vertebrates, Ghent University, K.L. Ledeganckstraat 35, 9000 Gent, Belgium sam.vanwassenbergh@ugent.be.
authors.forename: S
authors.initials: S
authors.lastname: Van Wassenbergh
authors.affiliation: Faculty of Mathematics and Natural Sciences, University of Groningen, Nijenborgh 7, AG Groningen 9747, The Netherlands.
authors.forename: K
authors.initials: K
authors.lastname: van Manen
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Los Angeles, 2154 Terasaki Life Sciences Building, Los Angeles, CA 90095, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Marcroft
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Los Angeles, 2154 Terasaki Life Sciences Building, Los Angeles, CA 90095, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Alfaro
authors.affiliation: Faculty of Mathematics and Natural Sciences, University of Groningen, Nijenborgh 7, AG Groningen 9747, The Netherlands Bionik Innovations Centrum, Hochschule Bremen, Neustadtswall 30, 28199 Bremen, Germany.
authors.forename: E J
authors.initials: EJ
authors.lastname: Stamhuis
mesh_terms: D000818:Animals; D057446:Hydrodynamics; D008954:Models, Biological; D013550:Swimming / Q000502:physiology*; D023721:Tetraodontiformes / Q000502:physiology*; D014867:Water
chemical_list: D014867:Water
keywords: boxfish; course stability; drag force; hydrodynamics; manoeuvrability; swimming