This study examined 396 base pairs of the mitochondrial cytochrome b gene from 110 individuals belonging to the genus Hampala, a group of freshwater cyprinids that inhabit Southeast Asia. The samples were taken from various locations throughout Sarawak, Sabah, and peninsular Malaysia. The nucleotide sequences were subjected to phylogenetic analyses by using the neighbor-joining, maximum parsimony, and maximum likelihood methods. All three methods revealed the reciprocally monophyletic relationship of Hampala macrolepidota to the other Hampala forms, thus strongly supporting its status as a distinct species. Phylogenetic analysis also discovered the existence of two H. bimaculata lineages endemic to Borneo: (1) a newly identified species from the southern and central part of Sarawak assigned as H. bimaculata Type A and (2) the previously described H. bimaculata from northern Sarawak and the west coast of Sabah assigned as H. bimaculata Type B. However, the status of H. sabana and an intermediate form were not elucidated. The results suggest that the intermediate form from the Tawau population is actually a subpopulation of H. sabana, while the highly divergent intermediate form from Kalabakan could represent a cryptic species. The sharing of H. macrolepidota haplotypes in the southern peninsular Malaysia and southern and central Sarawak samples (Hm1 and Hm2) reflected the recent disconnection of the two regions, during the late Pleistocene. Overall, the partial sequence of the mitochondrial cytochrome b gene was useful for resolving the phylogenetic relationships among Hampala fishes in Malaysia.
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