The Complete Mitochondrial Genome of the Freshwater Fish Onychostoma ovale (Cypriniformes, Cyprinidae): Genome Characterization and Phylogenetic Analysis.

In this study, we sequenced and characterized the complete mitochondrial genome (mitogenome) of Onychostoma ovale. The mitogenome of O. ovale was 16,602 bp in length with 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes, and a control region. The nucleotide composition of the O. ovale mitogenome was 31.47% A, 24.07% T, 15.92% G, and 28.54% C, with a higher A + T content (55.54%) than G + C content (44.46%). All PCGs began with the standard ATG codon, except for the cytochrome c oxidase subunit 1 (COX1) gene and the NADH dehydrogenase 3 (ND3) gene with GTG, while six PCGs ended with incomplete termination codons (TA or T). The Ka/Ks ratios of 13 PCGs were all less than one, indicating that they were under purifying selection. All tRNA genes were folded into the typical cloverleaf secondary structures with the exception of tRNA(Ser(AGY)), whose dihydrouridine (DHU) arm was absent. The phylogenetic trees showed that Onychostoma and Acrossocheilus were classified into three clades. There was a mosaic relationship between Onychostoma and Acrossocheilus. Moreover, the phylogenetic tree analysis showed that O. rarum was the closest species to O. ovale. This study can provide a useful resource for further phylogeny and population genetic analyses of Onychostoma and Acrossocheilus.