Genetic structure of natural populations of endangered Tor mahseer, Tor tor (Hamilton, 1822) inferred from two mitochondrial DNA markers

Tor tor, Tor mahseer, an endangered cyprinid species, is important as a sport fish. Genetic divergence in natural populations of T. tor was investigated using two mitochondrial genes, Cytb (Cytochrome b) and ATPase6/8. Analysis of 140 sequences of Cytb (1121 bp) and ATPase6/8 (842 bp) genes revealed 12 and 7 haplotypes, respectively, whereas 23 haplotypes were found in concatenated sequences (1963 bp). Sequence analysis of mitochondrial regions revealed balancing selection and displayed low nucleotide and moderate haplotype diversities. Mantel tests identified a positive relationship between pairwise geographical and genetic distances for the study region. Results of AMOVA based on genes pointed out that the genetic variations were mainly due to variation in within populations (ATPase6/8: 62.73%, Cytb: 42.13%, concatenated sequences: 48.31%). The total Fst was found to be significant in both genes with a value of 0.5787 (p <0 .05) and 0.3726 (p <0 .05) for Cytb and ATPase6/8genes respectively, whereas 0.51687 (p <0 .05) was found in combined sequences, which revealed sub-structuring in the T. tor natural populations. Population pair-wise Fst ranged from 0.00901– to 0.85631 for Cytb and 0.09910– to 0.64731 for ATPase6/8genes, whereas 0.02039 to 0.85436 in combined sequences. Results indicated the presence of four genetic stocks in the populations studied. The baseline information about stock characterisation in this study would be applicable for planning strategies for conservation, management and sustainable fisheries of this species.