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Sole searching
How we tested

How we tested: Using DNA to solve a mystery

Last reviewed: December 2011
Illustration of fish in a question mark
Illustration by Tom Garrett

An outside lab tested our fish samples using DNA bar coding, a recently developed, standardized way of identifying species. It uses a short DNA sequence that can be taken from raw, cooked, pickled, or smoked fish and compares it with the DNA of hundreds of thousands of specimens in newly available public databases. Searching a database is sort of like using Google, except you search with the letters of a DNA sequence instead of a word. So far, DNA bar coding has been used mostly by research organizations such as universities and museums.

Our project started with two staffers who served as mystery shoppers, buying a wide variety of fish from 55 stores and restaurants in fall 2010. The stores comprised 19 supermarkets, 13 fish markets, 12 gourmet and natural specialty stores, six restaurants, and five big-box stores.

We tested three samples or fewer of each type of fish from any store or restaurant, so we can't draw conclusions about the practices of chains or even individual retailers. And we bought all samples near the Consumer Reports headquarters in Yonkers, N.Y.: Results might differ if you order the same fish in your local market or restaurant.

In the stores

Our shoppers observed seafood display counters, placards, and menus, and asked questions. They noted each fish's country of origin and recorded whether it was labeled as wild or farmed and whether the label included sustainability claims. They noted prices, which ranged from $1.99 to $64.99 per pound. When buying whole fish, they asked the person behind the counter to cut it into fillets. "Many of the employees were not happy about doing this, especially with the cheaper fish," one of our shoppers says. "We received a lot of strange looks." At restaurants, the shoppers bought take-out orders of cooked seafood.

The shoppers placed the fish in refrigerated containers, froze them at our headquarters, then shipped them overnight to the lab.

Which fish were switched?

In descending order of percentage mislabeled, by species or group.

Chart showing which fish were switched