Vitamin D₃ and Its Metabolites Have No Role in Calcium and Phosphorus Metabolism in Tilapia mossambica

Abstract

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.