Predicting mercury concentration in fish using mass balance models

Mass balance models have frequently been used with laboratory-derived bioen ergetic models to examine the accumulation of mercury (Hg) in fish. The acc umulation of Hg in fish has usually been successfully described by these mo dels. However, this has generally been achieved by adjusting the parameters of these models until there was a close fit between observed and predicted values. In this study, we present a simple Hg mass balance model (MMBM) to predict Hg concentration in fish. This MMBM was applied with three methods of estimating food consumption rates to predict Hg concentration in three freshwater fish species. The MMBM accurately predicted the accumulation of Hg in the three fish species examined in this study when it was combined wi th food consumption rates that were determined with a radioisotopic method. The MMBM tended to underestimate Hg concentration in fish when it was comb ined with food consumption rates determined using laboratory-derived bioene rgetic models, possibly because activity costs derived under laboratory con ditions do not adequately represent activity costs of fish in the field. Wh en feeding rates were estimated with a bioenergetic model implemented with site-specific estimates of activity costs, the MMBM accurately predicted th e concentration of Hg in fish. Therefore, until activity costs can be accur ately estimated in situ, predictions obtained with the MMBM implemented wit h a laboratory-derived bioenergetic model should be interpreted cautiously.