Decoding Tuna

Tuna served in sushi restaurants may come from endangered species.
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Results from DNA barcoding research conducted by the Sackler Institute for Comparative Genomics at the American Museum of Natural History suggest that tuna sushi purchased in supermarkets might actually be healthier than that from restaurants. "We found that mercury levels are linked to specific species," Jacob Lowenstein, a graduate student affiliated with the Museum stated. "So far, the U.S. does not require restaurants and merchants to clarify what species they are selling or trading, but species names and clearer labeling would allow consumers to exercise greater control over the level of mercury they imbibe."

A quarter of restaurants, the study found, serve bluefin tuna, and some even sold escolar, a waxy fish banned for sale in Japan and Italy because of potential stomach illness. Genetic testing allowed researchers to pinpoint exactly which species were being served—including critically endangered Northern bluefin species.

This study also shows that all species tested exceed or approach mercury levels permissible by Canada, the E.U., Japan, the U.S., and the World Health Organization. Mercury levels were reported to be higher in bluefin akami and all bigeye tuna than in yellowfin. Although mercury typically accumulates in muscle, other factors affecting mercury content include size, age, body temperature and bioaccumulation.

Joanna Burger, professor at Rutgers University, said, "The levels of mercury in some tuna are sufficiently high to provide a health risk both to the fish themselves and to the predators that eat them, including humans, particularly those who eat fish frequently."

SOURCE: American Museum of Natural History.