Vitamin D3 and its metabolites have no role in calcium and phosphorus metabolism in Tilapia mossambica.

The physiological function of vitamin D in fishes still remains uncertain. Earlier we observed no relationship between vitamin D3 content of several freshwater fishes and their calcemic/phosphatemic status and bone mineral content. In the present study the effects of vitamin D3 and its metabolites, 25-hydroxy vitamin D3 (25-OH-D3) and 1,25-dihydroxy vitamin D3 [1,25-(OH)2D3], 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 D3 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 D3/1,25-(OH)2D3 at different levels and/or at various lengths of time. Thus these studies indicate that unlike in terrestrial vertebrates, vitamin D3 or its metabolites are not needed for calcium-phosphorus homeostasis in fish.