Even savvy consumers may be eating more mercury than they realize thanks to retail outlets in America mislabeling Chilean sea bass.

University of Hawaii scientists have found that Chilean sea bass certified by the Marine Stewardship Council are generally a healthier option than uncertified fish, but not always because of fishery-stock substitutions.

“Accurate labeling of seafood is essential to allow consumers to choose sustainable fisheries,” said UH Manoa biologist Peter Marko, lead author of the new study published in the scientific journal PLOS One, in a news release Monday. 

“But consumers also rely on labels to protect themselves from unhealthy mercury exposure. Seafood mislabeling distorts the true abundance of fish in the sea, defrauds consumers, and can cause unwanted exposure to harmful pollutants such as mercury.”

Fish market in Oahu's Chinatown

Fish market in Oahu’s Chinatown

Michelle Lee

Scientists had previously determined that 20 percent of fish purchased as Chilean sea bass were not genetically identifiable as such, the release says. Of the ones positively identified using DNA techniques, 15 percent had genetic markers that indicated that they were not sourced from the South Georgia fishery that MSC has labeled sustainable.

Scientists used the same fish samples to collect detailed mercury measurements.  When they compared the mercury in verified, MSC-certified sea bass with the mercury levels of verified, non-certified sea bass, they unexpectedly found no significant difference in the levels, the release says.

Chilean sea bass

Chilean sea bass in a grocery store.

“What’s happening is that the species are being substituted,” Marko said. “The ones that are substituted for MSC-certified Chilean sea bass tend to have very low mercury, whereas those substituted for uncertified fish tend to have very high mercury.  These substitutions skew the pool of fish used for MSC comparison purposes, making certified and uncertified fish appear to be much more different than they actually are.”

The UH study aside, another thing that may surprise consumers is learning that Chilean sea bass aren’t even a type of bass. They are actually Patagonian toothfish. Chilean sea bass is a name that someone made up a few decades ago so Americans would want to buy it.

Read the study here:

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