DNA 'Barcodes' Surface Fishy Imposters on Menus
Researchers Use Gene Segments to Settle Restaurant Mysteries, Check Stream Quality and Take Inventory of All Living Things
December 04, 2009
The Wall Street Journal
By Robert Lee Hotz
Researchers using a new DNA test recently discovered that fish ordered from menus in New York and Denver might not always be the species served. Sampling the fare at 31 sushi bars, scientists at the American Museum of Natural History found that customers who ordered tuna were sometimes served a cheaper substitute, an endangered species or a fish banned in several countries as a health hazard.
Scaled, sliced and hand-rolled, the eight most marketable species in the tuna genus Thunnus are prime candidates for honest error -- or bait and switch. On a plate, these wild tuna are almost identical, but sushi lovers especially prize the three species of bluefin tuna, whose annual catch was sharply curtailed last month. To identify the premium filets, the museum researchers singled out a short piece of genetic code naturally found in fish cells that, for the first time, can reliably label each of the eight species like a grocery store's inventory tag.
The researchers call it a DNA barcode.
More than a way to monitor menu mistakes, the development of the barcode arises from the need to tighten enforcement of regulations on tuna fishing. Regulators had no way to accurately identify which species of tuna had been sold, as required by an international convention on endangered species.
The museum researchers believe their DNA barcode, reported last month in the journal PLoS One, satisfies that requirement. "We want to be able to monitor the trade," says Sergios-Orestis Kolokotronis at the museum's Sackler Institute for Comparative Genomics, who helped conduct the study. Concerned about overfishing, the government of Monaco recently proposed a global ban on trade in the northern bluefin tuna species, which will be considered at a March meeting of the Convention on International Trade in Endangered Species in Qatar.
More broadly, the tuna DNA barcode is the latest application of genetic markers for biodiversity bookkeeping, which is quickly gaining international acceptance. Centers for DNA barcoding have opened recently in Canada and Mexico, with national facilities under development in China, France, Poland and the Netherlands.
The largest is the Biodiversity Institute of Ontario at the University of Guelph in Canada, where the technique was pioneered in 2003. There, researchers have culled barcode data from 750,000 specimens to create a reference library for about 100,000 species. "By 2015, I am confident we will have registered five million barcode records and at least 500,000 species," says Guelph biologist Paul Hebert.
As new barcode biomarkers become available, they are posted online in the Barcode of Life Data System, which encompasses findings from 300 global barcoding projects. The goal is nothing less than a DNA barcode for every living thing -- 10 million species or more.
Combined with traditional taxonomic techniques, a DNA barcode can make species identification as easy as name, rank and serial number.
Each of these inventory tags relies on a fraction of a single gene located in every cell's mitochondria. Unlike the genes in a cell's nucleus, though, this mitochondrial DNA isn't scrambled when the cell normally divides during reproduction. The gene segment mutates quickly enough so that scientists can distinguish closely related species but slowly enough that individuals of the same species have similar barcodes. With it, researchers can link tissue to its formal scientific identity and to all of the other specimens, field notes, lab studies and species data already on file.
"Used correctly, it is a great tool," says marine biologist Phaedra Doukakis at Stony Brook University in New York, who is using DNA tests to verify the labelling of commercial caviar.
As a practical matter, proponents promise that DNA barcodes will improve the international regulation of public health, agricultural imports and the environment. "We think the regulatory implications of this are really important," says David Schindel, executive secretary of the Consortium for the Barcode of Life at the Smithsonian Institution in Washington, D.C.
"This is something that has a number of applications and potential benefits in fisheries and the seafood market," says Jeremy Brown, vice president of the Commercial Fishermen of America. Techniques like DNA barcoding, he says, could give "the consumer the confidence to value the seafood they buy."
Already, U.S. regulators are trying it out. At the U.S. Environmental Protection Agency's national exposure research laboratory, population geneticist Mark Bagley is testing how quickly and accurately DNA barcodes can identify the insects whose presence or absence is used to gauge stream quality. The telltale insect larvae can be hard to distinguish from those of other aquatic bugs.
At the Smithsonian's feather identification laboratory, researchers use DNA barcodes to identify the remains of birds that flew into aircraft, handling 5,000 cases for the Federal Aviation Administration and the U.S. military so far this year. "You can't do anything about the problem until you know what it is," says ornithologist Carla Dove, who manages the laboratory.
In the Fish Barcode of Life Initiative, researchers so far have assembled DNA barcodes for 7,335 species of fish -- out of 30,000 known varieties.
At a minimum, they are hoping to dispel commercial confusion. Under U.S. regulations, for example, 33 species can be sold as grouper. Common market names are at odds with formal taxonomic labels and vary from region to region. One man's red mullet is another man's spotted goatfish.
When Dr. Hebert and his colleagues at Guelph last month tested fish at 18 restaurants in Canada, they found that almost half the orders served were mislabeled. "You order red snapper sushi, it is tilapia every time," says Dr. Hebert. University of North Carolina scientists in 2004 estimated that three-quarters of all snapper sold in the U.S. is mislabeled.
Likewise, the researchers from the American Museum of Natural History also found the sushi menu an unreliable guide. In all, they tested 68 servings of tuna sushi, ordering the raw fish at 31 eateries ranging from the Michelin-starred Nobu to a corner convenience store.
Their barcoding tests confirmed that sushi sold by Nobu as bigeye tuna was correctly labeled, but the tuna sold at half the other restaurants frequently was not, the researchers reported. Five of nine sushi servings sold as albacore tuna, for example, were actually a fish called escolar, which is banned in Italy and Japan because it can cause gastrointestinal illness.
Still, it will be a long time before a DNA barcoder shows up as a consumer appliance. For now, the lab test usually costs about $5 and takes 90 minutes or so.
Jacob Lowenstein, who devised the tuna DNA barcode, envisions an iPhone-like device that can produce instantaneous species identifications. "That's still far from reality," he says.
Write to Robert Lee Hotz at email@example.com