Stock assessment of <i>Schizothorax richardsonii</i> (Gray, 1832) using geometric morphometrics and mitochondrial marker COX1 from tributaries of the Chenab River, India

Schizothorax richardsonii (Gray, 1832) is extensively dispersed in the Indian Himalayan region and is recognized as an important source of animal protein. Geographical isolation between river ecosystems is believed to promote phenotypic and genotypic variation, ultimately leading to changes in the stock structure of aquatic species. With this aim of the study, 190 specimens of S. richardsonii were collected from four different tributaries, Rajouri Tawi, Chingus Tawi, Nowshera Tawi, and Ans River, of the Chenab River, to assess the intraspecific phenotypic and genotypic variations among stocks through landmark-based geometric morphometrics and mitochondrial marker COX1 gene. Three stocks were identified from four different tributaries of the Indus River basin. Principal Component Analysis (PCA) revealed that the first two principal components explained 76.89% of the total variance (PC1 = 67.67% and PC2 = 9.22%). The PC1-based shape wireframe showed that landmarks 5, 7, and 8 were crucial in distinguishing different morphotypes. The Canonical Variates Analysis (CVA) confirmed the existence of three morphologically distinct stocks within the Indus River basin. The COX1 sequence-based phylogenetic analysis also showed clear genetic differentiation among the stocks, supported by the Fst score-based heat map. These variations could be attributed to several factors, including uncommon hydrological conditions in these drainages, evolutionary pressures, and reproductive isolation among stocks. This study represents the first attempt to examine the stock structure of S. richardsonii using an integrated approach. The findings thoroughly explain species diversity and evolutionary dynamics in the Northwestern Himalayas and emphasize the importance of preserving genetic diversity and targeted conservation strategies to protect this ecologically significant species.