Phylogeography and morphological variation of <i>Mystus cavasius</i> in Indian rivers: Implications for conservation and fisheries management

This study examines genetic diversity using mitochondrial cytochrome b gene sequences and phenotypic variation through truss network and geometric morphometric analyses in Mystus cavasius populations from five major Indian rivers (Ganga, Brahmaputra, Mahanadi, Cauvery, and Krishna) along with a hatchery stock. Discriminant Function Analysis (DFA) identified significant morphological differences, mainly in the head, trunk, and caudal regions, although no clear population clusters were observed. Genetic diversity indices showed considerable haplotype variation in river populations, with the Ganga and Cauvery exhibiting the highest values, while the hatchery population displayed low genetic variance, indicating a single haplotype origin. Geographical and ecological factors played a key role in shaping genetic diversity among populations, as evidenced by hierarchical Analysis of Molecular Variance (AMOVA). Neutrality tests suggested demographic expansion in many populations, consistent with previous bottlenecks followed by population growth. Phylogenetic and haplotype network analyses revealed diverse genetic lineages, underscoring the influence of evolutionary and environmental factors. Phenotypic differences are driven by hydrobiological and geographic conditions, emphasizing the usefulness of truss morphometrics in detecting intraspecific diversity for effective fishery management. The results highlight the importance of conserving genetically distinct riverine populations and improved hatchery practices to minimize genetic homogenization, thereby supporting sustainable fisheries and conservation efforts.