Tuna fish identification using mtDNA markers

Abstract

Included in one of the most commercially valuable fishes traded all around the world, the genus Thunnus is a Scombridae which comprises eight nominal species commonly known as tunas. The most widely traded in the international fish market are the species known as Atlantic bluefin tuna (Thunnus thynnus), bigeye tuna, (Thunnus obesus), Southern bluefin tuna (Thunnus maccoyii), yellowfin tuna (Thunnus albacares), albacore (Thunnus alalunga), and Pacific bluefin tuna (Thunnus orientalis). As expected for congeneric species, they are morphologically very similar and the species identification, especially in its traded forms is difficult. Several protocols have been described for species identification of marine products; however, the low genetic distance between several tuna species commonly confound the obtained results depending on the molecular marker used. Additionally, several authors pointed that the use of the DNA barcoding methodology is not effective and cannot recognize all the species due to lack of resolution of this mitochondrial marker. Here we identified a potential region for species delimitation within the genus Thunnus. The mtDNA region between sites 8092 and 8847 which comprises the mtDNA genes ATP8, ATP6, and COX3 presented polymorphic sites which allow precise species delimitation. Moreover, it keeps the advantages of the DNA barcoding region in relation to fragment size (∼750bp) and conserved flanking regions for primer annealing. Flanking primers were developed and are now being tested with samples obtained from the local fish markets.