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Water flowing around an obstruction creates vortices (patterns of swirls) of varying size; by detecting the vortices, fish can determine the size and position of the obstruction. Testing by Yuzo R. Yanagisuru, Otar Akanyeti, and James C. Liao using models of three head shapes-narrow (low ratio of width to length), intermediate, and wide (high ratio of width to length)-showed that for large vortices, fish with intermediate heads would be better able than narrow-headed fish to distinguish between vortices and general turbulence in the water. A second research team has therefore hypothesized that in low-visibility conditions, intermediate-headed fish will be more likely than narrow-headed fish to detect obstructions that create large vortices.