Significant differences were observed in whole-body mercury concentrations in all treatments in week 0 compared to weeks 1, 2, 3, and 4 during the rearing period. In week 1, significant differences were found in whole-body mercury concentrations in all treatments compared to week 4. Only fish fed the 10% cysteine diet had significantly different whole-body mercury concentrations between week 1 and week 2. There were significant differences in whole-body mercury concentrations in fish fed the 0% and 10% cysteine diets in week 2 and in week 4. Between week 3 and week 4, the only significant difference in whole-body mercury concentration was observed between fish fed the 0% cysteine diets.