Unlocking mitogenomic analysis of Bagroides melapterus Bleeker, 1851 (Siluriformes: Bagridae) from Borneo: characterization and the placement within bagrids phylogeny.

The family Bagridae comprises a diverse group of freshwater catfishes distributed throughout Asia and Africa; however, several genera remain poorly represented in genomic studies. Among them, the monotypic genus Bagroides has lacked complete mitochondrial genomic data, limiting our understanding of its evolutionary history and phylogenetic position. Here, we report the first complete mitochondrial genome of Bagroides melapterus, providing the inaugural mitogenomic resource for the genus. The complete mitogenome of B. melapterus, a circular molecule of 16,542 bp with a GC content of 43.6%, was sequenced and characterized to elucidate its genetic composition and phylogenetic position. The mitogenome comprises 37 genes, including 13 protein-coding genes (PCGs), 22 transfer RNAs, 2 ribosomal RNAs, and a control region. Comparative analyses revealed a conserved genomic organization consistent with other members of Bagridae. To resolve its evolutionary placement, phylogenetic relationships were reconstructed using concatenated nucleotide sequences of the 13 mitochondrial PCGs and two rRNAs from representative bagrid taxa under Maximum Likelihood and Bayesian Inference frameworks, followed by divergence time estimation using a relaxed molecular clock. Both phylogenetic approaches recovered highly congruent topologies, consistently placing B. melapterus as the sister lineage of Pseudomystus siamensis with strong statistical support. Time-calibrated analyses indicated that these lineages diverged approximately 20.52 million years ago (mya) during the early Miocene, whereas the Sundaic Bagroides-Pseudomystus lineage separated from the common ancestor of the Tachysurus lineage around 44.89 mya in the mid Eocene. These divergence events coincide with major paleogeographic and climatic changes that likely contributed to the diversification of Southeast Asian freshwater fishes. As the first complete mitochondrial genome of Bagroides, this study fills a critical gap in the mitogenomic resources of Bagridae, refines the phylogenetic framework of the family, and provides an essential genomic foundation for future systematic, phylogenomic, and conservation studies of Asian freshwater catfishes.