Complete Mitochondrial Genome of the Endemic Loach Leptobotia tchangi and Its Phylogenetic Placement Within Botiidae

Background: Leptobotia tchangi is a loach species endemic to South China, but its mitochondrial genome has not yet been characterized, limiting understanding of its evolutionary relationships and conservation genetics. Methods: Here, we report the first complete mitochondrial genome of L. tchangi, using next-generation sequencing, assembly and bioinformatics analyses. Results: The double-stranded circular mitogenome has 16,590 bp and contains: 13 protein-coding genes (PCGs), 2 ribosomal RNA genes, 22 transfer RNA genes, and a non-coding control region (D-loop) containing conserved ETAS and CSB motifs. The overall base composition is 25.0% thymine (T), 27.9% cytosine (C), 31.1% adenine (A), and 16.0% guanine (G), showing a clear A + T bias (56.1%) which is consistent with other Botiidae mitogenomes. To infer the phylogenetic placement of L. tchangi within Botiidae, we conducted both Bayesian inference and maximum-likelihood phylogenetic analyses based on the concatenated PCG sequences. Our results strongly support (1) the monophyly of the subfamilies Leptobotiinae and Botiinae, as well as the monophyly of each genus within the family Botiidae; (2) three sister-group relationships within Botiinae: (Botia + Chromobotia), (Ambastaia + Sinibotia), and (Syncrossus + Yasuhikotakia), with the latter two species groups also being sister groups; (3) L. tchangi being most closely related to Leptobotia taeniops. Conclusions: These findings not only provide essential molecular markers for the species identification and conservation genetics of L. tchangi, but also clarify the taxonomic status of L. tchangi within Botiidae.