Elasmobranchs and Bony Fishes

Second, most of the mercury in the fish flesh was in the orgaiuc form, mainly methylmercury. This is because fish assimilate inorganic mercury less efficiently than methylmercury from the ambient medium and from their diet, and eliminate inorganic mercury more rapidly than methylmercury. Maximum concentrations of total mercury in shark and fish muscle usually did not exceed 2.0 mg Hg/kg FW however, forms of mercury with very low 

Fourth, total mercury was uniformly distributed in edible muscle of finfish, demonstrating that a small sample of muscle tissue taken from any region is representative of the whole muscle tissue when used for mercury analysis. 

Finally, elevated levels of mercury in wide-ranging oceanic fish were not solely the consequence of human activities but also resulted from natural concentrations. This last point is apparently not consistent with the rationale underlying U.S. Seafood guidelines regulating mercury levels in comestibles and formulated in the 1970s. When the U.S. Food and Drug Administration (USFDA) introduced safety guidelines - which eventually were instrumental in the temporary removal of all swordfish and substantial quantities of canned tuna from market - it acted essentially under the assumption that the fish product was adulterated by an added substance.  

It is noteworthy that muscle from two species of recreationally inportant fish spotted seatrout (Cynoscion nebulosus, red drum, Sciaenops ocellatus) collected from coastal bays in Texas considered minimally impacted by mercury exceeded the current recommended value in the U.S. of 0.3 mg total Hg/kg FW muscle. And walleye (Stizostedium vitreum vitreum) collected from Clay Lake, Ontario - a water body heavily contaminated by mercury wastes from a chloralkali plant between 1962 when discharges began and 1970 when the plant closed - contained 2.7 mg 

Of the 159 species of finfish, including sharks and rays, from coastal waters of Alaska, Hawaii, and the conterminous U.S., most muscle samples had mean concentrations less than 0.3 mg total Hg/kg FW. However 31 species contained more than 0.5 mg total Hg/kg FW, the action level set by the USFDA. These 31 species represented about 0.65% of the weight of the catch from the 159 species intended for human consumption. Extrapolation of these results indicate that less than 2% of the U.S. catch intended for human consumption may be in excess of the USFDA action level. Of the 31 species containing more than 0.5 mg total Hg/kg FW in muscle, ten were sharks and four were billfishes. 

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