Mercury in Marlin


Most people are unaware that marlin have been documented to accumulate harmful levels of mercury.  The U.S. Environmental Protection Agency health guidelines for fish consumption indicate that any fish with a mercury level greater than 1.5 parts per million (ppm) should not be consumed in any amount.   Marlin, especially large specimens, have been found to contain mercury levels as high as 15 ppm, or 10 times the EPA limit.

But recent research suggests that the toxicity of mercury may be cancelled out in some species of fish by the presence of sufficient quantities of selenium, a trace mineral that is important to the health of cells, in humans and other animals.  The relationship, and precisely how it works, is still under study; it appears the selenium binds with the mercury, blocking it from binding to brain tissue, for instance.  Because many fish contain selenium, mercury concerns are being downplayed, especially by the seafood industry.  They shouldn’t be.  

It’s agreed among researchers that the key factor is the ratio of selenium (Se) to mercury (Hg).  A high Se:Hg ratio would mean the selenium makes the mercury benign, with enough left over for its own benefits to cellular function.  If the ratio is low, for example, more mercury than selenium, then the mercury can is harmful and there are no nutritional benefits from the selenium.  Those fish with high Se:Hg ratios include salmon, tuna and red snapper.  Those fish with the lowest ratios include swordfish, shark and marlin.  According to a 2007 study using fish purchased in the U.S., marlin steaks contained twice as much mercury as selenium (Se:Hg ration of 1.45:2.89 ppm), making it the most potentially toxic fish examined. (Sivakumar et al, Trace Elements in Fish and Fish Oil Supplements, Atomic Spectroscopy, March 2007)   


National Coalition for Marine ConservationInternational Game Fish Association