The influence of sodium fluoride (NaF) on calcium metabolism was examined in goldfish (fresh water teleost). At
2 days after administration of NaF (500 ng/g bodyweight; 5 μg/g bodyweight) (around 10−5 to 10−4  Mingoldfish),we indicated that plasma calcium levels upregulated in both doses of NaF-treated goldfish. To examine the mecha-nism of hypercalcemia by NaF treatments, therefore, direct effects of NaF on osteoblasts and osteoclasts in goldfishwere investigated by an original assay systemusing teleost scalewhich has steoblasts, osteoclasts and bonematrix. Alkaline phosphatase activity in the scales increased with the treatment of NaF 10−6 and 10−5 M) during 6 h of incubation. Also, tartrate-resistant acid phosphatase activity increased after exposure to NaF (10−5 M) at the 6 h of incubation. To investigate the osteoclastic activation, the mRNA expression of osteoclastogenesis related factors were examined. The receptor activator of the nuclear factor-κB ligand (RANKL) which is known as a factor for oste-oclastogenesis, increased in the NaF-treated scales after 6 h of incubation. The ratio of RANKL/osteoprotegerin (os-teoclastogenesis inhibitory factor) significantly increased after 6 h of incubation. Resulting from the increase of RANKL mRNA level, the expression of transcription-regulating factors was significantly increased. Furthermore, the expression of functional genes, cathepsin K and matrix metalloproteinase-9 mRNA, was significantly increased. In our knowledge, this is the first report concerning the effects of NaF on osteoblasts and osteoclasts in teleosts.We concluded that NaF influences calcium metabolism via osteoclastic activation in goldfish.