Mitogenomic Evidence for the Phylogenetic Placement of Chimarrichthys kishinouyei Within Sisoridae

Background: The phylogenetic placement of the rheophilic glyptosternoid catfish Chimarrichthys kishinouyei within Sisoridae remains insufficiently resolved because mitogenome-derived phylogenetic evidence has been unavailable. Methods: We sequenced, assembled, and annotated the complete mitogenome of C. kishinouyei and reconstructed its mitochondrial phylogenetic relationships using 13 protein-coding genes and two rRNA genes. Results: The mitogenome was a circular molecule of 16,718 bp and contained 37 typical mitochondrial genes, including 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a control region. The genome showed an A + T bias, with an A + T content of 57.27%. Most tRNAs formed typical cloverleaf structures, whereas tRNA-Ser(GCU) lacked a typical DHU arm. Codon usage was biased, and all 13 protein-coding genes had Ka/Ks ratios below 1, consistent with predominant purifying selection. Phylogenetic analyses placed C. kishinouyei within the glyptosternoid lineage and recovered a strongly supported sister relationship with Pareuchiloglanis sichuanensis rather than direct clustering with Euchiloglanis davidi. Conclusions: Phylogenetic analyses based on 13 protein-coding genes and two rRNA genes support the placement of C. kishinouyei within glyptosternoid Sisoridae and indicate that relationships among Chimarrichthys, Pareuchiloglanis, and Euchiloglanis require further testing with broader integrative evidence.