DNA damage, histological changes and DNA repair in larval Japanese medaka (Oryzias latipes) exposed to ultraviolet-B radiation.

Cyclobutane dimer formation, photorepair capability and histological damage were compared among four differently pigmented strains of larval Japanese medaka (Oryzias latipes) to determine whether pigmentation modifies the level of UV-B radiation (290-320 nm) inducible damage in these fish. One-day post-hatch medaka were exposed to one of several UV-B fluence rates with or without photoreactivating light for 5 days for 7 h per day. Their DNA was extracted for analysis by ELISA for cyclobutane pyrimidine dimers or the larvae were processed for histological examination. At the higher UV-B fluence rates tested, wild-type melanophore-containing medaka formed significantly more dimers than at least one of the other strains tested. Wild-type medaka also showed significantly less photorepair capability than the white melanophore-lacking medaka. The wild-type larvae had significantly more necrosis than the orange-red melanophore-lacking larvae at the lower UV-B fluence rate tested and at the higher fluence rate used, the wild-type medaka also exhibited significantly more necrosis than the white melanophore-lacking larvae. Of the 19 medaka observed with cellular hyperplasia, six were wild-type. These six individual larvae showed the greatest degree of cellular hyperplasia. Cellular hyperplasia appeared to be greatest at the lowest UV-B fluence rate used. The presence of melanophores in the wild-type medaka may have contributed to an increased level of tissue damage in this strain when compared to the other strains.