Mitochondrial Cyt b Reveals Low Diversity and Basin-Scale Population Structure in Black Carp (Mylopharyngodon piceus) from the Yangtze, Pearl and Red River Basins

) is an ecologically and economically important freshwater fish native to China and neighbouring regions, but its wild stocks have declined sharply in recent decades. We analysed mitochondrial cytochrome b (Cyt b) sequences from 100 individuals collected in 2008-2009 from four Yangtze River, two Pearl River and one Red River populations to assess genetic diversity and structure as a pre-ban baseline for maternal lineages. Sixteen polymorphic sites defined 17 haplotypes, with a single dominant haplotype (Hap2) shared across all populations. Haplotype diversity was high but nucleotide diversity low, and neutrality tests together with mismatch-distribution analyses were consistent with a recent Late Pleistocene demographic expansion. Pairwise FST values ranged from negligible differentiation among middle-lower Yangtze populations to pronounced differentiation between the upstream Yangtze population (SS) and middle-lower populations and between the Yangtze and the combined Pearl-Red basins, whereas Pearl and Red River populations showed no significant divergence and high mitochondrial homogeneity, consistent with substantial historical connectivity. Overall, the Cyt b data indicate low mitochondrial diversity and shallow but significant inter-basin structuring, providing preliminary mtDNA-based evidence that Yangtze and Pearl-Red populations represent candidate conservation and management units, and highlighting the need for nuclear genomic markers and contemporary sampling to refine drainage-scale units and evaluate recent management effects.