Significance of the succession and/or the disappearance of ultraviolet photosensitivity in the Antarctic fish suborder Notothenioidei

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This study aimed to investigate mechanism of the succession and/or the disappearance of ultraviolet photosensitivity in the teleosts. To achieve this aim, Antarctic fishes suborder Notothenioidei, which accomplished evolution in Antarctic sea endemically, were used for analyzing ultraviolet opsin gene and histological presence of UV-photoreceptor(UV-cone) in their retina.1) The UV-cone presented in more endemic 6 families. In the 7th family Bthydraconidae, speceis having UV-cone and not-having were intermingled. Further, the channichthyid species which are most specialized in Antarctica lost UV-cones. Therefore, it was guessed that the UV-cone is a character being lost during the process of speciation in this suborder.2)The full length UV-opsin gene was 1008bp and encoded 336 amino acids. Phylogenetic analysis of UV-opsin genes among 9 species in 3 families expressed a possibility it correspond to speciation of nototheniid species.3)In the retina of juvenile Champsocephalus gunnari belonging to Channichthyidae, the UV-cone presented and UV-opsin gene was isolated. Therefore, in channichthyiids, it was supposed that even if UV-cone was lack in adult fish, the juvenile fish have the UV-cone and express UV-opsin mRNA in their retina.4)The blue-, green- and red-opsin gene was 1056, 1056 and 1068bp and encoded 352 and 356 amino acid residues, respectively. Lower homology was shown for blue- and green-opsins than red-opsin between other teleost genes. This may indicate that fish evolved adaptively in light environment of their habitat depth or place, and then evolved blue- and green-opsin genes species-specifically