Mitochondrial DNA diversity of broodstock of two indigenous mahseer species, Tor tambroides and T. douronensis (Cyprinidae) cultured in Sarawak, Malaysia

Tor tambroides and T. douronensis, locally referred to as empurau and semah, respectively, are high valued mahseer species, indigenous to Sarawak, East Malaysia, with an aquaculture potential and of conservational value. Direct sequencing of mitochondrial DNA (mtDNA) 16S rRNA gene region (542 bp) was used to investigate genetic variation of T. tambroides and T. douronensis broodstock collected from different geographic locations in Sarawak and maintained at the Indigenous Fish Research and Production Center (IFRPC), Tarat, Sarawak, Malaysia. A total of 11 unique haplotypes were identified, of which six were detected in T. tambroides, and five in T. douronensis. Overall, nucleotide diversity (π) was low, ranging from 0.000 to 0.006, and haplotype diversity (h) ranged from 0.000 to 0.599. Although the analysis failed to detect genetic variation amongst populations of T. tambroides (significant pairwise FST was found for only one test, but pairwise haplotype frequencies were not statistically significant), substantial inter-population divergence among T. douronensis was recognised, especially those originating from different river systems (pairwise F_ST = 0.754 to 1.000, P < 0.05). Fixed haplotype differences were found in one population of T. douronensis. Average nucleotide divergence between T. tambroides and T. douronensis was 0.018, similar to the amount recognised between T. tambroides and the outgroup T. khudree (0.017). In addition, phylogenetic analysis revealed that the T. douronensis mtDNA consisted of two highly divergent clusters (0.020), one of which is more closely related to T. tambroides rather than with the other group of haplotypes of the conspecifics. The findings from the present study have important implications for aquaculture, management and conservation of these two species. The data also raise some concerns regarding the taxonomic status of T. douronensis, which needs to be addressed.