Mitochondrial Genomes of Six Discogobio Species (Teleostei, Cyprinidae) and Their Phylogenetic Analysis

Discogobio is an important small freshwater economic fish in Southwestern China. In this study, we determined the complete mitochondrial genome (mitogenome) sequences of six Discogobio species by conventional overlapping PCR and Sanger sequencing. The mitogenomes were 16,591-16,605 bp in length and contained 13 protein-coding genes, 22 transfer RNA genes, two ribosomal RNA genes, and a noncoding region, which was consistent with previously studied Labeoninae mitogenomes. The phylogenetic analysis revealed that the subfamily Labeoninae was divided into four major clades. Notably, Discogobio was observed to be a non-monophyletic group and mixed with Discocheilus. The divergence time of Discogobio and Discocheilus can be placed during the time of the most recent common ancestor in the late Miocene (7.80 Mya). The results of the selection pressure analyses indicated that all Discogobio fishes exhibited Ka/Ks ratios < 1, suggesting that mitochondrial function in this genus was subjected to strong purifying selection and adapted to different environments. These mitogenomes will facilitate further studies in phylogeny, taxonomy, and evolutionary biology related to the subfamily Labeoninae.