Research Article: The Real maccoyii: Identifying Tuna Sushi with DNA Barcodes – Contrasting Characteristic Attributes and Genetic Distances

Date Published: November 18, 2009

Publisher: Public Library of Science

Author(s): Jacob H. Lowenstein, George Amato, Sergios-Orestis Kolokotronis, Jon R. Bridle.

Abstract: The 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.

Partial Text: 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]. As sushi, 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. As a result, in a recently published sushi advisory guide, a collective of conservation organizations urged consumers to avoid eating bluefin altogether [3]. Efforts to extend the public’s appreciation of bluefin beyond sushi highlight iridescent grandeur [4], [5]: fish that can exceed a ton in weight [6], reach speeds of over 50 km/h [7], cross ocean basins [8], depths and temperatures [9]–[11], returning to spawn in the same ancestral waters [12] fished by people for millennia [13]. 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. Distinguishing bluefin’s smallest essence, its DNA, plays a role in cultivating conscientious consumerism and effective regulation by eliminating market ambiguity.

Of the 68 samples from 31 establishments (Table 1), eight were listed on menus as bluefin, 4 as albacore, 1 as bigeye, and 1 as yellowfin tuna. There was no written description as to which species was being served for the other samples. For this latter group, when asked for verbal clarification as to what species was being served, 20 were said to be bluefin (with no indication as to which species), 17 as bigeye tuna, 4 as yellowfin tuna, 1 as dorado (Coryphaena hippurus), 3 as “tuna” (ambiguous but correct by the U.S. Food and Drug Administration standards), 3 as “red tuna,” 2 as “white tuna,” and 1 as “mackerel tuna.” One sample (JHL403) was excluded as the interviewer slipped and used a leading question with the example “yellowfin” to query the species. The identity of two pieces identified on the menu as white tuna was not verbally queried. Price per order ranged between US$2.25 and $15 and ranged in mass between 9 and 40 grams.



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