Abstract
A number of contaminants affect fish health, including mercury and selenium, and the selenium:mercury molar ratio. Recently the protective effects of selenium on methylmercury toxicity have been publicized, particularly for consumption of saltwater fish. Yet the relative ameliorating effects of selenium on toxicity within fish have not been examined, nor has the molar ratio in different tissues, (i.e. brain). We examined mercury and selenium levels in brain, kidney, liver, red and white muscle, and skin and scales in bluefish (Pomatomus saltatrix) (n=40) from New Jersey to determine whether there were toxic levels of either metal, and we computed the selenium:mercury molar ratios by tissues. Total mercury averaged 0.32±0.02ppm wet weight in edible muscle and 0.09±0.01ppm in brain. Selenium concentration averaged 0.37±0.03 in muscle and 0.36±0.03ppm in brain. There were significant differences in levels of mercury, selenium, and selenium:mercury molar ratios, among tissues. Mercury and selenium levels were correlated in kidney and skin/scales. Mercury levels were highest in kidney, intermediate in muscle and liver, and lowest in brain and skin/scales; selenium levels were also highest in kidney, intermediate in liver, and were an order of magnitude lower in the white muscle and brain. Mercury levels in muscle, kidney and skin/scales were positively correlated with fish size (length). Selenium levels in muscle, kidney and liver were positively correlated with fish length, but in brain; selenium levels were negatively correlated with fish length. The selenium:mercury molar ratio was negatively correlated with fish length for white muscle, liver, kidney, and brain, particularly for fish over 50cm in length, suggesting that older fish experience less protective advantages of selenium against mercury toxicity than smaller fish, and that consumers of bluefish similarly receive less advantage from eating larger fish.
► We examine mercury:selenium ratios in internal tissues of bluefish in New Jersey. ► Mercury and selenium levels were highest in the kidney and lowest in the brain. ► The selenium:mercury molar ratio was negatively correlated with fish length for all tissues. ► Levels of selenium and mercury in tissues, including brain, were generally below toxic levels.