L-responses to UV stimulus and UV sensitive cones in marine fishes. To examine the UV sensitivity of marine fishes, the L-responses to monochromatic UV of 337 nm and 368 nm were recorded from the retinae of 11 fishes. 5 species, including Chelidonichthys spinosus （A group）, showed L-responses to both the wavelengths, Pagrus major and Sparus sarba （B group）, showed L-responses only to 368 nm, and the other 4 species, including Konosirus punctatus （C group）, showed no response to the UV stimulus. Histological examination of the retinae revealed that all these fishes had twin cones but no small accessory corner cones. Twin cones and central single cones formed cone mosaics in a regular arrangement in A and B groups, and central single cones were missing missing in most cone mosaics in C group. These experimental results indicate that the central single cone is sensitive to the UV used.