SILVER UPTAKE BY THE OYSTER (CRASSOSTREA-VIRGINICA) - EFFECT OF ORGANISM SIZE AND STORAGE SITES

Three sizes of hatchery-reared oysters (mean sizes 32, 66 and 104 mm) were exposed to 0 (control), 2 and 7 mug l-1 added Ag for 1 and 2 weeks. Control oysters exhibited no change in soft tissue Ag concentration, but exposed tissue concentrations generally increased with exposure concentration and duration for all sizes. Silver body burdens generally increased with size, but because of large dry weight differences, tissue concentrations of small oysters were up to 20 times those of large oysters. Large oysters (93 mm) were also exposed to 0, 2 and 7 mug l-1 added Ag for 2 weeks and then analysed for Ag in various tissues both before and after spawning. Highest concentrations as well as largest increase in tissue concentrations of pre-spawning oysters were found in the gonads, with the following order: gonads>gills>muscle>residue. In post-spawning oysters, gills and mantle concentrations were higher than residue and muscle, but none of these tissues contained levels as high as in pre-spawning gonads. A high concentration of Ag in the gonads allows oysters to rapidly reduce Ag body burdens in summer through spawning.