Preferential left-eye use during mirror inspection in five species of fishes

We recently found 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 (Bisazza et al., Anim. Behav. in press). This 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. Indirect evidence for this has been obtained using detour tests: when faced with a vertical-bar barrier through which a target was visible, female mosquitofish showed a consistent bias to turn left when the target was a predator and to turn right when the target was a conspecific of the same gender. We measured the time spent in monocular viewing during inspection of their own mirror images in females of five species of fish, belonging to different families - Gambusia holbrooki, Xenotoca eiseni, Phoxinus phoxinus, Pterophyllum scalare, Xenopoecilus sarasinorum. Results revealed a consistent left-eye preference during sustained fixation in all of five species. 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 images of conspecifics.