Taxonomic and guild structure of fish assemblages in the streams of Western Himalaya, India.
Local environmental and anthropogenic variables play a key role in determining the species distribution across the riverscape. The upstream of River Ganga flows through the Western Himalaya that is unique due to wide variation in hydro-geomorphological features, which offer microhabitats for many fish species. Thus the present study was aimed to investigate the role of environmental and anthropogenic variables on taxonomic and guild structures of the fish assemblages in streams of the Western Himalaya. We documented fish assemblages along the altitudinal gradients in streams of Western Himalaya with 20 sampling sites covering both Bhagirathi and Alakhnanda basins of the upper Ganga river. We documented 40 species of fishes belonging to 12 ecological guilds. We observed high species turnover in streams that flow between 400 and 800 m altitude, while there was no fish species recorded in streams located above 2400 m altitude. Twelve environmental and three anthropogenic variables were subjected to PCA for removing redundant variables, and the linearly uncorrelated variables were then used in the redundancy analysis (RDA) to test the effects of environmental and anthropogenic variables on structuring the species and guild assemblages. We found four distinct fish species assemblages groups in three distinct guilds. The RDA results revealed more number of species associated in sites that were faraway distance from the source with greater catchment areas. Greater number of species inhabited the deep and wide stream with high substrate diversity. The ordination of environmental and anthropogenic variables with ecological guild showed that the upstream basin area and water velocity were highly correlated for members of BISSL guild (Benthic dweller-Insectivore-Small size-Simple reproduction strategy-Local migrant). The members of typical rheophilic minnows belonging to SISSL guild (Surface dweller-Insectivore-Small size-Simple reproduction strategy-Local migrant) were strongly related to close proximity to dams. Further, the proximity of dam was negatively correlated with native snow trout, Schizothorax richardsonii distribution, and the dam presence was positively correlated with the presence of non-native carp, Cyprinus carpio in the Western Himalaya. We could confirm the increase in species richness with decreasing altitude in Western Himalaya.