Mercury distribution in the muscular tissue of farmed southern bluefin tuna (Thunnus maccoyii) is inversely related to the lipid content of tissues

The lipid content and total mercury concentration were measured in whole tissue composites of all edible tissues of farmed southern bluefin tuna (Thunnus maccoyii) and each of the marketed tissue cuts of these fish (akami, chu-toro, o-toro). Despite differences in fish size, condition factor and culture time, the mercury concentrations of tissue cuts and composite samples were found to decrease with increasing lipid content at a consistent rate of −0.00476 Hg (mg/kg)/% lipid within each fish. Consequently, lipid accumulation appears to have a dilution effect on mercury already associated with fish tissues. The increased affinity of lipid for certain tissue cuts (o-toro) over that of others (e.g. akami), results in cross carcass variation in the mercury concentration of fish muscular tissue with clear implications for mercury advisory statements – the tissue sample collected for analysis is critical.