DNA barcoding of Scomberomorus (Scombridae, Actinopterygii) reveals cryptic diversity and misidentifications

The genus Scomberomorus is economically important; however, the taxonomic status and phylogenetic relationships in this genus are not clearly resolved, making it difficult to effectively protect and exploit fish resources. To clarify the taxonomic status of Scomberomorus species, mitochondrial cytochrome c oxidase I (COI) gene sequences of 150 samples were analyzed. The average genetic distance among 14 species was approximately 11 times greater than the distances within species, in accordance with the '10× rule' of species identification. Five of the 14 species did not form monophyletic clades based on a Bayesian inference gene tree. The application of four DNA-based species delimitation methods (automatic barcode gap discovery, barcode index numbers, Poisson tree process, and the K/θ method) yielded several key results. (1) Cryptic species were detected within Scomberomoruscommerson. (2) A Scomberomorusqueenslandicus sample from Australia was misidentified as S.commerson in the Barcode of Life Data System (BOLD). (3) Specimens originally identified as Scomberomorusguttatus was differentiated into four OTUs or species, two in the Yellow, South China, and Java seas, and two in geographically distant areas, one each in the Arabian Sea and the Bay of Bengal. (4) Six specimens from South Africa originally identified as S.plurilineatus most likely do not belong to the species. (5) Specimens identified as S.maculatus and S.regalis were conspecific; however, introgression cannot be ruled out. Our findings revealed cryptic diversity and difficulties in morphological identification of species in the genus Scomberomorus. This study provides scientifically based support for the conservation of germplasm resources of the genus Scomberomorus.