Mitogenomic architecture of Acheilognathus imberbis (Actinopterygii, Cypriniformes, Cyprinidae): Implications for Acheilognathinae phylogeny

The complete mitochondrial genome of Acheilognathus imberbis Günther, 1868, a small freshwater fish inhabiting tributaries of the Yangtze and Yellow River systems, was sequenced and characterized. The circular mitogenome spans 16 576 base pairs, containing 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes, and a non-coding control region. Nucleotide composition analysis revealed an AT-rich genome (A + T = 58.93%) with distinct guanine deficiency (15.88% G content), consistent with a typical vertebrate mitogenome bias. To resolve debated phylogenetic relationships within Acheilognathinae, we performed phylogenetic analysis using concatenated sequences of 13 PCGs from 37 representative species. Results confirmed the monophyly of Acheilognathinae, which diverged into two primary clades: Acheilognathus and the Tanakia–Rhodeus complex. Notably, the monophyletic status of Rhodeus received limited nodal support, suggesting potential taxonomic revisions. Pairwise genetic distances (Tamura–Nei model) ranged from 0.0071 to 0.2600 across the subfamily. Through homology analysis, some Acheilognathinae fishes are clustered together, and the genetic distance is much less than 0.0406, suggesting re-evaluation of their classification criteria. Positive selection analysis based on the ND2 gene using site models revealed no statistically significant codon positions under positive selection. This mitogenomic resource advances molecular systematics and evolutionary studies in Acheilognathinae fishes.