The physiological function of vitamin D in fishes still remains uncertain. Earlier we observed no relationship between vitamin D
3 content of several freshwater fishes and their calcemic/phosphatemic status and bone mineral content. In the present study the effects of vitamin D
3 and its metabolites, 25-hydroxy vitamin D
3 (25-OH-D
3) and 1, 25-dihydroxy vitamin D
3 [1, 25-(OH)
2D
3], administration on serum calcium-phosphorus levels, intestinal calcium absorption, whole-body calcium-phosphorus uptake, and gill calcium binding protein (CaBP) activity in the freshwater fish,
Tilapia mossambica (Tilapia) was examined. It was observed that vitamin D
3 and its metabolites could alter neither serum calcium-phosphorus levels nor intestinal calcium absorption and gill CaBP activity in fish at various doses. Further, the whole-body uptake of labelled calcium and phosphorus was also unaffected by vitamin D
3/1, 25-(OH)
2D
3 at different levels and/or at various lengths of time. Thus these studies indicate that unlike in terrestrial vertebrates, vitamin D
3 or its metabolites are not needed for calcium-phosphorus homeostasis in fish.
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