1Research Institute for Ocean Economics, Minato, Tokyo 105-0003, 2Department of Marine Science and Technology, Tokyo University of Fisheries, Minato, Tokyo 108-8477, Japan
The change in visual acuity and retinal adaptation according to light intensity was investigated for red sea bream Pagrus major. Visual acuity was estimated by a behavioral training method as 0.24 in 500lx, 0.19 in 100lx, 0.15 in 10lx and 0.10 in 1-0.1lx. Retinal adaptation was examined by a histological method in fish exposed to the same light condition as a behavioral experiment. The pigment index was 72.8-65.8% in 500-1lx and 42.0% in 0.1lx. From the results of behavioral experiments and histological experiments, it was suggested that the visual cells of red sea bream shift to rods from cones between an illumination strength of 1lx and 0.1lx.