What tuna are you eating?

The latest  meeting of the international commission created to manage harvests of tunas and other wide-ranging fish species in the Atlantic Ocean ended by setting 2010 quotas for bluefin tuna that  conservation groups and  United States fisheries officials said were -- while lowered -- still far too high to allow the imperiled fish to recover. (from DotEarth)

The government of Monaco proposed a ban on international trade of bluefin tuna, and was  initially supported by the European Union and the U.S. It won't be hard for people who know the fish to recognize bluefin if whole fish are being shipped, but what if they've already been processed into steaks or filets? What then?

A little over a year ago a couple of high school students from Manhattan pointed the way. They used DNA fingerprinting to identify samples of sushi at New York restaurants and found that 25% were misidentified.

Jacob Lowenstein and his colleagues develop a more sophisticated DNA barcode based on cytochrome C oxidase subunit I to distinguish among all tuna species in the genus Thunnus (the genus to which bluefin belongs). They sampled tuna sushi from 31 restaurants in Manhattan and Denver. Among the 68 samples they tested they found some that were from endangered tuna species, some that weren't what they said, and some that were a health hazard.

Five out of nine samples sold as a variant of "white tuna" were not albacore (T. alalunga), but escolar (Lepidocybium flavorunneum), a gempylid species banned for sale in Italy and Japan due to health concerns. Nineteen samples were northern bluefin tuna (T. thynnus) or the critically endangered southern bluefin tuna (T. maccoyii), though nine restaurants that sold these species did not state these species on their menus.

The take home message? I see two. First, Lowenstein and colleagues demonstrate yet again that DNA barcoding can be a useful tool in identifying commercially sold fish (and other products). Second, think twice next time you order a piece of maguro at your favorite sushi bar and ask yourself how confident you are that it's not bluefin (and that the folks who run your sushi bar would know the difference or care).