Boxfish swimming paradox resolved: forces by the flow of water around the body promote manoeuvrability

S. Van Wassenbergh*, K. van Manen, T. A. Marcroft, M. E. Alfaro, E. J. Stamhuis

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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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.

Original languageEnglish
Article number20141146
Number of pages11
JournalJournal of the Royal Society Interface
Issue number103
Publication statusPublished - 6-Feb-2015


  • boxfish
  • hydrodynamics
  • manoeuvrability
  • course stability
  • swimming
  • drag force
  • FINS

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