Relationship among mercury concentration, growth rate, and condition of northern pike: A tautology resolved?

Methylmercury is a bioaccumulative contaminant that biomagnifies in aquatic food webs and adversely affects the health of freshwater fish. Previous studies have documented an inverse relationship between fish condition and concentration of mercury in fish. However, this relationship may be a result of slow-growing fish accumulating large amounts of methylmercury rather than the effects of methylmercury on fish condition and growth. An evaluation was conducted of the relationship among fish condition, growth, and mercury concentration in northern pike Esox lucius from 26 lakes in the western region of the Laurentian Great Lakes (USA-Canada). The relative weight (an index of fish condition) of northern pike was inversely related to mercury concentration in the axial muscle. The concentration of mercury in standard-size northern pike increased with fish age and suggested that fast-growing fish accumulated less mercury than slow-growing fish. However, there was no relationship between the mean relative weight of northern pike in each population and mean age or mercury concentration of standard-size northern pike. These results suggest that the relationship between mercury and fish condition is not because of the effects of mercury on rate of growth, but rather because slow-growing fish bioaccumulate greater concentrations of mercury than fast-growing fish of the same length. Environ Toxicol Chem 2016;35:2910-2915. © 2016 SETAC.