A biologist walks into a sushi bar and orders some tuna. What does he get? Escolar, a nasty fish with buttery flesh that can cause bizarre episodes of diarrhea, accompanied by a waxy intestinal discharge.

It's not a joke. It happened five times to the same scientists during a brief research project. The results of that study were published Wednesday in PLOS One.

"A piece of tuna sushi has the potential to be an endangered species, a fraud or a health hazard," wrote the authors. "All three of these cases were uncovered in this study."

The team of researchers from Columbia University and the American Museum of Natural History ordered tuna from 31 sushi restaurants and then used genetic tests to determine the species of fishes in those dishes. More than half of those eateries misrepresented, or couldn't clarify the type of fish they were mongering. Several were selling endangered southern bluefin tuna.

Although their results were shocking, exposing sloppy sushi joints wasn't their main goal. The scientists were trying to improve on a new species-identification technique, called DNA barcoding. A coalition of labs has been collecting fish, reading their genes and uploading the information to a database called FISH-BOL.

Their goal is to build a catalog of every fish species on earth so that anyone with a handheld DNA reader could definitively identify fish within minutes. Wildlife officials could use that technology to spot-check fish markets, and fine people who are selling protected species.

Right now, the FISH-BOL database is roughly 20 percent complete, but zooligsts can't seem to agree upon the best way to condense the genetic information from each fish into a concise signature. That's where this study comes into play. By checking 14 carefully selected spots on a gene called cox1 and matching them up with the database, the scientists could accurately identify any kind of tuna.

Citation: Lowenstein JH, Amato G, Kolokotronis S-O, "The Real maccoyii: Identifying Tuna Sushi with DNA Barcodes – Contrasting Characteristic Attributes and Genetic Distances." PLoS ONE 4, 11, 2009, e7866.

Photo: Spicy tuna roll

stuart_spivack/Flickr

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