Mercury comparisons between farmed and wild Atlantic salmon (Salmo salar L.) and Atlantic cod (Gadus morhua L.)

Wild and farmed Atlantic salmon (Salmo salar L.) and Atlantic cod (Gadus morhua L.) were collected to assess changes in mercury with size in wild vs. farmed fish. Mercury concentrations were compared with Health Canada and United States Environmental Protection Agency consumption guidelines. Lipid dilution of mercury was examined by comparing lipid-extracted (LE) and non-lipid-extracted (NLE) flesh samples in both farmed and wild fish. Mercury concentrations in the flesh and liver of farmed salmon were significantly lower than concentrations in wild salmon of similar fork length (P < 0.001), possibly due to growth dilution in rapidly growing farmed fish. Mercury concentrations were higher in LE tissue compared with NLE (P < 0.05), suggesting lipid dilution of mercury in farmed fish with a high lipid content. Farmed cod, which do not grow more rapidly than wild cod, did not have significantly different flesh and liver concentrations compared with wild cod of similar fork length (P > 0.05). Between species of farmed fish, cod had significantly higher mercury concentrations than salmon (P < 0.05), but neither farmed nor wild salmon mercury concentrations exceeded federal consumption guidelines. These results suggest that rapid growth rates and a high lipid content may play important roles in regulating concentrations of contaminants such as mercury.