Abstract
BackgroundThe use of DNA barcodes for the identification of described species is one of the least controversial and most promising applications of barcoding. There is no consensus, however, as to what constitutes an appropriate identification standard and most barcoding efforts simply attempt to pair a query sequence with reference sequences and deem identification successful if it falls within the bounds of some pre-established cutoffs using genetic distance. Since the Renaissance, however, most biological classification schemes have relied on the use of diagnostic characters to identify and place species.Methodology/Principal FindingsHere we developed a cytochrome c oxidase subunit I character-based key for the identification of all tuna species of the genus Thunnus, and compared its performance with distance-based measures for identification of 68 samples of tuna sushi purchased from 31 restaurants in Manhattan (New York City) and Denver, Colorado. Both the character-based key and GenBank BLAST successfully identified 100% of the tuna samples, while the Barcode of Life Database (BOLD) as well as genetic distance thresholds, and neighbor-joining phylogenetic tree building performed poorly in terms of species identification. A piece of tuna sushi has the potential to be an endangered species, a fraud, or a health hazard. All three of these cases were uncovered in this study. Nineteen restaurant establishments were unable to clarify or misrepresented what species they sold. 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.Conclusions/SignificanceThe Convention on International Trade Endangered Species (CITES) requires that listed species must be identifiable in trade. This research fulfills this requirement for tuna, and supports the nomination of northern bluefin tuna for CITES listing in 2010.
Highlights
The cognomen ‘‘bluefin tuna’’ encompasses three distinct species: southern bluefin tuna (Thunnus maccoyii, Castelnau 1872), Pacific bluefin tuna (T. orientalis, Temminck & Schlegel 1844), and northern bluefin tuna (T. thynnus, Linnaeus 1758) [1]
Albacore, and Pacific bluefin tuna all had a single nucleotide at each diagnostic site, whereas the nucleotides for the other species were not fixed at some positions yielding multiple compound characteristic attributes (CAs)
The Utility of cox1 for Thunnus Identification This research demonstrates that tuna fish species can be reliably identified with cox1 barcodes using either our character-based key or highest BLAST sequence similarity
Summary
The cognomen ‘‘bluefin tuna’’ encompasses three distinct species: southern bluefin tuna (Thunnus maccoyii, Castelnau 1872), Pacific bluefin tuna (T. orientalis, Temminck & Schlegel 1844), and northern bluefin tuna (T. thynnus, Linnaeus 1758) [1]. Bluefin are unrivaled in popularity, and the economic value per fish unmatched by any other species [2]. Immediate demand for bluefin has far outpaced efforts for long-term management threatening the persistence of this species triad. In a recently published sushi advisory guide, a collective of conservation organizations urged consumers to avoid eating bluefin altogether [3]. Efforts to garner reverence for bluefin—and with it a popular prohibition against consuming them—are limited because tuna sushi is often made with less imperiled species. The use of DNA barcodes for the identification of described species is one of the least controversial and most promising applications of barcoding. Since the Renaissance, most biological classification schemes have relied on the use of diagnostic characters to identify and place species
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