Boxfish shape aids swimming ability

Scientists have discovered how boxfish manage to swim so effectively when they are blessed with such a ridiculously impractical body shape.

A team of scientists from the Department of Biological Sciences, Old Dominion University, Norfolk, Virginia, studied three different boxfish to see what methods they used to help them to swim and found that each one produced swirly flow patterns called leading-edge vortices (LEVs) capable of generating self-correcting trimming forces during swimming.

Their findings are reported today in a paper in the Journal of Experimental Biology.

Each of the three ostraciid boxfish studied, including the spotted boxfish, scrawled cowfish and buffalo trunkfish, produced LEVs that grew in circulation along the bodies.

The team says that similar flow patterns have also been recorded around delta-winged aircraft.

By using a combination of very sophisticated techniques, the scientists were able to determine how the flow patterns produced by the fish formed.

They found that the spiral vortices formed above the keels and increased in circulation as the angle of the pitch got bigger. On the underside they increased in circulation as the angle became more negative.

The team concluded that the carapace of the boxfish was actually well-designed to correct poor swimming:

\"Although other features of the carapace also affect flow patterns and pressure distributions in different ways, the integrated effects of the flows were consistent for all forms: they produce trimming self-correcting forces, which we measured directly using the force balance.

\"These data together with previous work on smooth trunkfish indicate that body-induced vortical flows are a common mechanism that is probably significant for trim control in all species of tropical boxfishes.\"

For more details see the paper: Bartol IK, Gharib M, Webb PW, Weihs D, Gordon MS. (2005) - Body-induced vortical flows: a common mechanism for self-corrective trimming control in boxfishes. J Exp Biol. 2005 Jan 15;208(Pt 2):327-44.