Preferential left and right eye-use in fish: Concordance between different methods

We measured the time spent in monocular viewing during inspection of their own mirror images in females of three species of fishes (Xenotoca eiseni, Gambusia holbrooki and Xenopoecilus sarasinorum), using a rectangular-shaped tank in which animals could observe their own reflection in two mirrors positioned along the major walls, and in females of five species of fishes (Xenotoca eiseni, Gambusia holbrooki, Xenopoecilus sarasinorum, Danio rerio and Gnatonemus petersii), using a quasi-circular tank in which the animals could rotate clockwise or anticlockwise and observe their own reflection 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 apparatus, though in the quasi-circular tank fish showed more variability of response. The asymmetry was apparent during the first 5 minutes 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 vertebrate species, with a preferential involvement of structures located to the right side of the brain in response to the viewing of images of conspecifics.