SIZE-RELATED CHANGE IN THE VISUAL RESOLUTION OF SUNFISH (LEPOMIS SPP)

Visual resolution of juvenile sunfish (Lepomis spp.) (8-33 mm standard length (SL)), although extremely poor in comparison with the larger i ndividuals (38-160 mm SL) used in previous studies, improves rapidly a s they grow. Histologically and behaviorally determined (mean reaction angle) visual angles of fish between 10 and 33 mm SL decrease by appr oximately 50 and 100 minutes of are, respectively, and decline nonline arly with increasing fish size. Behaviorally determined visual resolut ion of juvenile sunfish based on maximum location distance (MLD) is eq uivalent to that calculated from intercone spacing. The mean reaction angle used in previous studies may have underestimated behavioral Visu al resolution of larger (>38 mm SL) sunfish by approximately 30%. Visu al volume and search volume increase by nearly three orders of magnitu de in sunfish between 8 and 50 mm SL. After sunfish exceed 50 mm SL (w hen they can safely return to the pelagic zone), visual resolution inc reases comparatively slowly as body size increases. Our results sugges t that the size-related change in behavioral visual resolution in sunf ish is influenced by other factors in addition to the growth-related c hanges in the resolving power of the retina.