Vitamin D3 compounds induce hypermelanosis on the blind side and vertebral deformity in juvenile Japanese flounder Paralichthys olivaceus

The purpose of the present study was to investigate the effect of vitamin D-3 com- pounds on the occurrence of hypermelanosis on the blind side and vertebral deformity in juvenile Japanese flounder Paralichthys olivaceus. To elucidate the mechanism by which vitamin D-3 causes hypermelanosis in Japanese flounder, larvae (total length (TL), 9.8 +/- 0.77 rhm; 22 days post-hatching (dph)) were fed an artificial diet without any vitamin D supplement (control group), a diet supplemented with 0.5 mg vitamin D-3/100 g (VD3 group), or a diet supplemented with 0.05 mg 1,25-dihydroxyvitamin D-3/100 g (1,25(OH)(2)D-3 group) until 49 dph. Fish were harvested at 49 dph and 70 dph for assessment of the TL, survival, pigmentation, and vertebral deformity. A high incidence of hypermelanosis on the blind side was observed on the head and caudal regions in all groups at both 49 dph and 70 dph. A significantly higher frequency of occurrence of severe hypermelanosis on the trunk region of the blind side was observed in the 1,25(OH)(2)D-3 group (P < 0.05) compared with the control group at 70 dph. Moreover, completely hyperpigmented fish were observed only in the 1,25(OH)(2)D-3 group. A higher frequency of the occurrence of winding of the abdominal vertebrae was also observed in the VD3 and 1,25(OH)(2)D-3 groups (P < 0.05).