Uptake and loss of dissolved zinc by the stickleback Gasterosteus aculeatus L.

Uptake and loss by sticklebacks of both stable zinc and 65Zn in hard and soft water have been studied for periods of upto400 h. In calcium‐free water, the 65Zn uptake curve is approximately asymptotic over a period of 24 h, while in hard water internal 65Zn levels are dropping at 24 h. Over 5 h, however, fish in hard tapwater absorb about 3.5 times more 65Zn than those in calcium‐free water. There is a positive linear relationship between log 65Zn uptake and log wet weight of fish. Whole‐body concentration factors (c.f.) at 16 h reach a maximum of 12.2 (mean=2.9), highest concentrations of 65Zn being found in the gills (mean c.f.=5.l) and lowest concentrations in the gonads (mean c.f.=0.8). Over longer periods (400 h), internal stable zinc levels offish exposed to 1 and 4 p.p.m. Zn2+ remain little higher (max 28 %) than controls. 65Zn efflux into zinc‐free water falls to zero after 5 h, more zinc (78 %) being lost after uptake in tapwater than in calcium‐free water (56 %).