Complete mitochondrial genomes of two catfishes (Siluriformes, Bagridae) and their phylogenetic implications

The mitochondrial genome (mitogenome) has been widely used as a molecular marker to investigate phylogenetic analysis and evolutionary history in fish. However, the study of mitogenomes is still scarce in the family Bagridae. In this study, the mitogenomes of Tachysurusbrachyrhabdion and T.gracilis were sequenced, annotated, and analyzed. The mitogenomes were found to be 16,532 bp and 16,533 bp, respectively, and each contained 37 typical mitochondrial genes, which are 13 protein-coding genes (PCGs), 22 tRNA genes, two rRNA genes, and a control region. All PCGs begin with the codon ATG, except for the cytochrome c oxidase subunit 1 (COI) gene, while seven PCGs end with an incomplete termination codon. All tRNA genes can fold into their typical cloverleaf secondary structures, except for tRNA(Ser(AGY)), which lacks the dihydrouracil arm. The Ka/Ks ratios for all PCGs are far lower than one. Phylogenetic analyses based on Bayesian inference (BI) and maximum likelihood (ML) showed that the two clades in Bagridae excluded Ritarita. The monophyly of Tachysurus supports previous research and the traditional classification that Leiocassis, Pseudobagrus, Pelteobagrus, and Tachysurus belong to one genus (Tachysurus). These findings provide a phylogenetic basis for future phylogenetic and taxonomic studies of Bagridae.