DNA barcoding and taxonomic validation of Caranx spp. larvae

Of the five nominal species in the genus Caranx Lacepède 1801 distributed throughout the Eastern Central Pacific, Caranx caballus and Caranx sexfasciatus are the only two that have formal fish larval descriptions based on diagnostic characteristics (morphology, meristics and pigmentation). In this study, the diagnostic characteristics of three Caranx species larvae were validated using DNA barcoding analysis cytochrome c oxidase subunit I (COI; 651 bp). For the first time, the morphological taxonomic assignation of C. caballus fish larvae was confirmed using COI gene partial sequences of adults, with a genetic similarity between 99.8-100%. However, molecular evidence demonstrated that fish larvae previously described as C. sexfasciatus had high genetic similarity (99.7-100%) and low genetic distance (<1%) to Caranx caninus adults. An undescribed larval morphotype collected in the present study genetically matched (100%) with COI sequences of C. sexfasciatus adults. The diagnostic characteristics of this new morphotype were a lack of pigmentation in the supraoccipital crest, over the gut, and at the terminal region of the gut. The combination of diagnostic characteristics and DNA barcoding evidence allowed the discrimination and validation of C. caballus, C. caninus and C. sexfasciatus larvae. The diagnostic characteristics and COI sequences of Caranx lugubris and Caranx melampygus larvae, which are also distributed in the Eastern Central Pacific, remain to be investigated.