The mahseers (Tor spp.) are among the most ecologically, culturally, and economically significant freshwater fishes in Southeast Asia. Despite their importance, the taxonomic distinction between T. cf. tambra and T. cf. tambroides in Thailand and Peninsular Malaysia remains problematic because of overlapping morphological characteristics and the absence of genetic reference sequences anchored to name-bearing type specimens. In this study, three mitochondrial markers, COX1, 16S rRNA, and the D-loop, were used to investigate phylogenetic relationships and genetic diversity among Tor populations from Thailand and Peninsular Malaysia. COX1 phylogenetic reconstruction and species-delimitation analyses recovered four principal mitochondrial groups. G1, provisionally designated as T. cf. tambra, contained the majority of the examined samples from Thailand and Peninsular Malaysia. G2 comprised samples from the Salween River and was treated as an unresolved Tor lineage. G3 was subdivided into G3-1, an unresolved mitochondrial lineage represented by two Malaysian samples and one GenBank sequence reported from Java, and G3-2, provisionally designated as T. cf. tambroides based on Sumatran GenBank sequences. G4 comprised GenBank sequences provisionally designated as T. cf. douronensis. Population genetic analyses based on D-loop sequences revealed strong geographic structuring among populations from northern, central, and southern Thailand and Peninsular Malaysia, with comparatively weaker differentiation among populations within the same region. The occurrence of divergent mitochondrial lineages in aquaculture stocks, particularly at Hulu Langat and Endau, suggests possible broodstock translocation or mixing. Overall, our results reveal substantial mitochondrial diversity within the Tor tambra–T. tambroides complex and provide a genetic framework for future taxonomic, conservation, and aquaculture studies.
Tor tambra, Tor tambroides, Mitochondrial DNA, Phylogenetics, Species delimitation
