Morphometric and genetic insights into intraspecific variations in <scp>Himalayan</scp> snow trout ( <i>Schizothorax richardsonii</i> ) across major <scp>Indian Himalayan river</scp> drainages

Schizothorax richardsonii (Gray, 1832), commonly known as snow trout, is a widely consumed food fish in the cold-water drainages of the Himalayas and serves as a significant source of animal protein for communities living along the riverbanks. This study examined morphological and genetic variations in six stocks of S. richardsonii from the Ganga and Chenab river systems in the Central and Western Indian Himalayas, utilizing the truss network analysis and mitochondrial COX1 gene marker. A total of 268 fish samples were collected for morphometric analysis, of which 34 were used for genetic study, from six distinct locations between August 2021 and July 2022. Various statistical analyses were performed, including univariate analysis of variance (ANOVA), multivariate analysis of variance (MANOVA), principal component analysis (PCA), discriminant analysis of principal components (DAPC), canonical discriminant function analysis (CDFA) and boxplot analysis. Seventy-one morphometric measurements of fish showed statistically significant variations (p < 0.01) among six locations of the two river basins forming six different fish stocks. The origins of the dorsal, pectoral fins and eye diameter were found to be important parameters in morphological discrimination. Furthermore, sequencing and analysis of the mitochondrial COX1 gene of 34 specimens of S. richardsonii revealed the highest haplotype (0.80000) and nucleotide (0.00265) diversities in the Pindar River. A newly emerged haplotype, Hap_7, was identified in the Rajouri Tawi. Phylogenetic analysis showed clear geographical divergence among the populations. Canonical correspondence analysis (CCA) identified morphometric variations that were attributed to differences in water velocity and transparency of the selected drainages, whereas genetic variations were associated with differences in water temperature, prolonged geographical isolation, geological changes and reproductive isolation between populations. Our study provides a comprehensive understanding of the morphometric and genetic population structure and evolutionary dynamics, which will help resolve the taxonomic ambiguity and suggest potential population structure and indicate possible management units for this vulnerable species.