Effects of 1,25- and 24,25-dihydroxyvitamin D3 on bone formation in the cichlid teleost Sarotherodon mossambicus

1,25-Dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 have antagonistic effects on the acellular bone of the tilapia Sarotherodon mossambicus. 1,25-Dihydroxyvitamin D3 inhibits the activity of the lining osteoblasts. Prolonged administration leads to demineralization of the bone matrix. Injection of 24,25-dihydroxyvitamin D3 induces structural signs of greatly enhanced appositional bone growth within three days. No effects were observed on the mineral content of pre-existing bone. Both 1,25- and 24,25-dihydroxyvitamin D3 may have distinct, but different physiological functions in fish.