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Abiotic factors in the riverine ecosystem are important in structuring fish communities along the longitudinal gradients. Quantitative data on species abundance were collected during October 2015-September 2016 in the mountain stretch of the River Western Ramganga from Kumaun Lesser Himalayas, India. Multivariate analyses were done to study the relationship between fish assemblages and abiotic parameters. Cluster analysis and non-metric multidimensional scaling indicated two distinct groups in the upstream and downstream zones. The composition of fish assemblages in different zones was found to be strongly associated with habitat characteristics. Canonical correspondence analysis revealed species abundance association with temperature, conductivity, stream width and altitude. Further analysis showed conductivity-altitude combination as the primary factor determining the longitudinal distribution of species composition in the studied stretch of this river. The present study aids in understanding the factors that determine the spatial segregation of species for the restoration, conservation and management of aquatic resources. [ABSTRACT FROM AUTHOR]