Wiley, Journal of Applied Ichthyology, 4(30), p. 671-677, 2014
DOI: 10.1111/jai.12513
Full text: Download
Calcium is of vital importance in vertebrates and plasma levels are tightly regulated. Terrestrial vertebrates depend for their calcium uptake exclusively on the diet, while fish have an essentially infinite directly accessible source of calcium in the surrounding water. The need to store calcium seems thus less evident in fish. It was the goal of the present study to investigate the possible role of the scale compartment of zebrafish (Danio rerio) as an accessible pool for calcium and phosphorus. We restricted the calcium availability to zebrafish both in water and diet. Following 12 days restriction, we found that scalar contents of calcium and phosphorus had declined, while magnesium was unaffected, indicating resorption of calcium hydroxyapatite. Osteoclast activity on scales of calcium-restricted fish increased, as we conclude from enlarged demineralized areas on scales, increased TRAcP activity staining, and higher ctsk gene expression. Osteoblasts respond to calcium limitation by increasing expression of col1a2 and alpl. In the presence of water and dietary calcium, removal of scales from one flank of the fish does not affect scalar mineral contents, scale demineralization and osteoclastic TRAcP activity; expression of sp7, alpl and ctsk are up-regulated. Apparently, a high demand for calcium in zebrafish is preferentially complemented with exogenous calcium, while calcium is recruited from the scales when environmental calcium is limited. We conclude that the scales represent an important deposit of available calcium and phosphorus from which these minerals can be recruited in periods of high demand. This finding contributes to a niche for scales as model in bone research.