Roots of brain specializations: Preferential left-eye use during mirror- image inspection in six species of teleost fish.

It has recently been reported that predator inspection is more likely to occur when a companion (i.e., the mirror image of the test animal) is visible on the left rather than on the right side of mosquitofish Gambusia holbrooki. This very unexpected outcome could be consistent with the hypothesis of a preferential use of the right eye during sustained fixation of a predator as well as of a preferential use of the left eye during fixation of conspecifics. This study measured the time spent in monocular viewing during inspection of their own mirror images in females of 6 species of fish, belonging to different families. Results revealed a consistent left-eye preference during sustained fixation in 5 of the species. Males of G. holbrooki, which do not normally show any social behavior, did not exhibit any eye preferences during mirror-image inspection. It was found, however, that they could be induced to manifest a left-eye preference if tested soon after capture, when some affiliative tendencies can be observed. These findings add to current evidence in a variety of vertebrate species for preferential involvement of structures located in the right side of the brain in response to the viewing of conspecifics.