The capability of fish to synthesize vitamin D on exposure to ultraviolet (UV) light was examined. Purposeful exposure of the freshwater fish
Tilapia mossambica (Tilapia) to artificial UV light (300 nm) resulted in a significant increase of vitamin D
3 with a concomitant decrease in provitamin D
3 [7-dehydrocholesterol (7-DHC) ], indicating that provitamin D
3 was coverted to vitamin D
3. However, only 0.13% of the intraperitoneally injected 4-
14C cholesterol was recovered in the vita-min D
3 and 25-hydroxyvitamin D
3 (25-OH-D
3) fractions after 15 h of irradiation. Thus, although fish is capable of photosynthesizing vitamin D through constant, prolonged exposure to UV light of appropriate wave-length, the contribution of this mode of synthesis is unlikely to be of any significance in its natural habitat.
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