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Researchers Use New Approach to Identify Threatened Tuna Species

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DNA barcoding is not only a useful taxonomic technique, but it can also help save endangered species and verify the accuracy of your dinner menu, says a study done by researchers at the American Museum of Natural History. The team used DNA barcoding to prove that bluefin tuna, a species currently threatened by over-fishing, is routinely served in sushi restaurants in New York and Colorado where it is mislabeled as another type of fish.

Earlier efforts to identify tuna using DNA barcodes have had less than satisfying results due to the relatedness of the eight tuna species that make up the Thunnus genus. Previously used methods of identifying bluefin with DNA barcoding have typically utilized a short mitochondrial DNA sequence from the cox-1 gene, chosen for its variability and specificity, along with a Blast-like algorithm to search through the Barcode of Life database to construct a distance measure from the sequence in question to the sequences for a known species in the database. However, this method has a somewhat arbitrary cut-off and there's a question about whether it's a good identifier or not.

The AMNH team instead successfully identified closely related species by creating a genetic key based on 14 nucleotide positions contained in cox-1. "We think our research is valuable for demonstrating that barcoding is actually a good identifier for these species. [That] has a lot of applications, but also it informed the barcoding community that you may want to use this approach when you're analyzing your barcode data," says George Amato, director of the Sackler Institute for Comparative Genomics at AMNH. "This is a very straightforward application of molecular technology — we're only talking about sequencing 650 bases. It's something that can be easily done in any laboratory."

Amato and his colleagues are now setting their sights on developing other applications for their approach as well as ways to make the process more portable. "If you were monitoring the trade in fish, you don't need 100,000 species — you need 200 species, so you could probably have those sequences all on a chip and get an accurate identification," he says. "We're thinking about how this can be applied more directly now that we've sort of done the proof-of-concept research."

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