What causes lateralization of detour behavior in fish? Evidence for asymmetries in eye use.

A consistent population bias to detour a vertical-bar barrier preferentially leftwise during approach to inspect a dummy predator was demonstrated in the poeciliid fish Girardinus falcatus. The asymmetry seems to be due to a preferential use of the lateral visual field of the right eye during fixation of biologically relevant stimuli such as a predator. Viewing tests revealed in fact that fish which tended to detour the barrier on the left side used the right eye to scrutiny a dummy predator and the left eye to scrutiny a neutral stimulus, whereas fish which tended to detour the barrier on the right side showed the reverse pattern of eye use; fish that did not show any consistent bias in the detour test did not reveal any significant preference in the viewing test.