This Patagonian toothfish tends to be marketed as Chilean Sea Bass.

At the grocery store, you may forego a less sustainable variety of fish to pick up a Marine Stewardship Council (MSC) vetted choice.

But increasingly, there are good reasons for consumers to question what fish they are actually purchasing.

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Such is the case with the Patagonian toothfish (Dissostichus eleginoides), usually marketed as Chilean sea bass. After examining mitochondrial DNA from fish purchased at retail outlets in eight different states, researchers found 8 percent of 36 fish samples were a different species of fish entirely.

Their findings, featured in the journal Current Biology, reveal the packaged fish didn’t originate from off the coast of the island South Georgia (part of the South Sandwich Islands) — the only sustainable place to harvest the fish at this time. Researchers looked at 1,200 nucleotides of mitochondrial DNA from the fish to distinguish whether they came from the same genetic population.

And of the remaining 33 samples that belonged to the species, 15 percent possessed genetic information uncharacteristic of the South Georgia area. For comparison, about half of the non-certified products sampled seem to have been harvested from other Antarctic waters, where populations aren’t managed sustainably.

The species has been overfished in the past because of its slow maturity (it starts reproducing relatively late). Experts have advised against common fishing practices such as trawling used to catch the fish, which can unintentionally harm other marine wildlife.

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After scientists published the study, the non-profit MSC released a response, detailing the organization’s plan to launch an investigation into the Chilean sea bass claims. It states the MSC previously used DNA testing to rule out false claims in the same species and will take away responsible parties’ certification if necessary. At present, the MSC works with 258 fisheries around the world.

To be fair, it’s unlikely all MSC choices are misleading or false, and it’s obvious many fisheries and businesses play by the rules because they care about their products and the planet. But the study at hand highlights a chink in the system’s eco-friendly armor that needs to be addressed.

Somewhere along the line — whether the fish have been harvested by people who don’t uphold the MSC’s mission or want to make money, MSC’s labeling system may have misled consumers into thinking they’re making sustainable choices while depleting vulnerable populations.

But the problem isn’t limited to Chilean sea bass.

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With a handful of sustainable populations to take from, even the most vulnerable species of tuna still find their way to our dinner plates and sushi bars, according to another blog post.

Resources such as the Monterey Bay Aquarium’s project Seafood Watch give consumers the dirt on their possible seafood choices. The organization slapped an “avoid” on the Chilean sea bass profile because of overfishing and concerning mercury levels.

Photo by U.S. FDA/Wikimedia Commons