Spatio-temporal variation in fish assemblages and factors affecting them in the Madi River, Nepal

ABSTRACT Understanding spatial and temporal variations in fish assemblages within river systems is vital for evaluating their ecological significance and predicting the impacts of anthropogenic activities. Despite the economic and ecological importance of freshwater fisheries in Nepal, limited information is available on mid-hill rivers. We investigated the spatio-temporal dynamics and environmental factors influencing fish abundance and species richness in the Madi River, Nepal, from 2021 to 2023. We conducted seasonal sampling across different elevations using electrofishing. We recorded 26 fish species belonging to four orders, seven families, and 17 genera. Cypriniformes was the dominant order, while Cyprinidae represented the most abundant family. The Canonical Correspondence Analysis revealed that environmental variables, temperature and dissolved oxygen influenced fish assemblages. Spatio-temporal clustering showed higher similarity among sites during summer and autumn, whereas greater variation was observed in winter. Fish assemblage composition was varied among sampling sites (R=0.506; p