Lateralization of response to social stimuli in fishes

We measured the time spent in monocular viewing during inspection of their own mirror images in females of three species of fish (Xenotoca eiseni, Gambusia holbrooki and Xenopoecilus sarasinorum) using a rectangular tank in which fishes could observe their own reflections in two mirrors positioned along the major walls, and in females of five species of fish (X. eiseni, G. holbrooki, X. sarasinorum, Danio rerio and Gnatonemus petersii) using a quasi-circular tank in which fish could rotate clockwise or counterclockwise and observe their own reflections in a mirror positioned along the outer wall. Results revealed a consistent left-eye preference during initial sustained fixation in all species irrespective of the type of apparatus. However, in the quasi-circular tank apparatus, fish showed more variability of response. The asymmetry was apparent during the first 5 min of observation and tended to fade thereafter, probably as a result of habituation. These findings add to current evidence for a quite invariant pattern in the direction of lateralization in similar tasks in a variety of vertebrates species, with a preferential involvement of structures located to the right side of the brain in response to the viewing of images of conspecifics.