ABSTRACT The anadromous Hilsa shad ( Tenualosa ilisha ) is a commercially and ecologically important fish species distributed across the Bay of Bengal, the Arabian Sea, and the river systems of South and Southeast Asia and the Middle East. Despite its significance, the genetic diversity, population structure, and demographic history of T. ilisha populations are poorly understood, particularly across the regions. This study provides the first comparative genetic analysis with extensive sampling of T. ilisha populations from Bangladesh and Iraq, utilizing mitochondrial DNA markers—Cytochrome C Oxidase subunit I ( COI ) and Cytochrome b ( CYTB ) genes—to assess genetic variation, population connectivity, and evolutionary history. A total of 279 individuals were collected from nine locations representing coastal, riverine, estuarine, mangrove forest, and floodplain environments, and 267 mitochondrial DNA sequences from the two genes ( COI and CYTB ) were analyzed using concatenated datasets. Genetic analyses revealed significant inter‐regional genetic differentiation, with Bangladeshi populations exhibiting higher genetic diversity, while Iraqi populations displayed genetic homogeneity. Population structure analyses using analysis of molecular variance and F‐statistics (F ST ) demonstrated strong genetic differentiation between Bangladeshi and Iraqi populations, with inter‐regional variation accounting for over 69% of the total genetic variation. Intraregional differentiation was low among Bangladeshi populations, suggesting gene flow, whereas Iraqi populations showed no significant genetic differentiation, indicating a single, genetically uniform stock. Haplotype network analyses supported inter‐regional isolation and intraregional connectivity, with no shared haplotypes between Bangladesh and Iraq. Demographic analyses indicated recent population expansion in most Bangladeshi populations, whereas the Iraqi populations exhibited demographic stability. Expansion events in Bangladesh occurred during the late Pleistocene. Overall, the findings highlight contrasting genetic patterns between the two regions and emphasize that T. ilisha should not be considered a single panmictic stock. These results provide important insights for developing region‐specific conservation and management strategies for sustaining hilsa fisheries.
Alam et al. (Wed,) studied this question.
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