Abstract
Retinal structure in marbled sole was examined microscopically in their early developmental stage to estimate a linkage of changes of visual ability with the caudal fin loss. Photoreceptor cells in the pre-metamorphosis stage were comprised of single cones exclusively. During metamorphosis, adjacent single cones formed double cones, while a regular square mosaic pattern composed of four double cones surrounding one single cone appeared in post-metamorphosis stage. These morphological changes were assumed to improve the visual ability. As one of possible causes for caudal fin loss, biting other individuals is considered to increase by the help of the improved visual sense.
