Size-related Change in the Visual Resolution of Sunfish (Lepomis spp.)

Visual resolution of juvenile sunfish (bepornis spp.) (8-33 mm standard length (SL)), although extremely poor in comparison with the larger individuals (38-1 60 mm SL) used in previous studies, improves rapidly as they grow. Histologically and behaviorally determined (mean reaction angle) visual angles of fish between 10 and 33 mm SL decrease by approximately 58 and 100 minutes of arc, respectively, and decline non-linearly with increasing fish sine. Behaviorally determined visual resolution of juvenile sunfish based on max-imum location distance (MSD) i s equivalent to that calculated from intercone spacing. The mean reaction angle used in previous studies may have underestimated behavioral visual resolution of larger (>38 mrn Sk) sunfish by approximately 30%. Visual volume and search volume increase by nearly three orders of mag-nitude in sunfish between 8 and 50 rnm SL. After sunfish exceed 50 mm SL (when they can safely return to the pelagic zone), visual resolution increases comparatively slowly as body size increases. Our results suggest that the sine-related change in behavioral visual resolution in sunfish i s influenced by other fac-tors i n addition to the growth-related changes in the resolving power of the retina. La resolution visuelle chez de jeunes crapets (bepornis spp.) (de 8 33 rnm de Bongueur standard (LS), bien qu'extremement faible, comparativement aux iwdividus plus grands (38 A 160 mm de LS) utilises dans les etudes precedentes, augmente rapidement a mesure qu'iis grandissent. kes angles visuels (angles d