Physicochemical Parameters of Water and Their Effects in Temporal Variation of Fish Composition in Lower Reaches of Mahakali River, Nepal

Water quality shapes aquatic fauna. However, no information is available about water quality and its effect on fish diversity of Mahakali River. This study was conducted to measure the temporal variation of physicochemical parameters of water and their effects on fish composition in the lower reaches of Mahakali River, Nepal in between September 2022 to August 2023. Measurements of water quality parameters and fish collection were carried out on a monthly basis. Shannon–Weiner diversity index was calculated to measure fish diversity and multiple regression analysis was computed to analyze the effects of physicochemical parameters of water in fish composition. This study revealed that physicochemical parameters of water at lower reaches of the river were in the range of fish tolerance and support good fish diversity (H = 3.06). Changing physicochemical parameters of water, instead of affecting the overall species, affected the species-specific manner and had significant effect on the species composition of Anguilla, Schizothorax, Mystus, Amblyceps, Bagarius, Ompok, Garra, Acanthocobitis, Schistura, Lepidocephalichthys, Xenentodon, Mastacembelus, Glossogobius and Channa fish species but had no effect on the species composition of Salmophasia, Barilius, Raimas, Puntius, Tor, Chagunius, Labeo and Botia. This study suggests that in snow fed perennial river high fish diversity, dominated by cyprinids, is found in autumn followed by winter season associated with clear river water, moderate temperature and more hardness in water containing more total dissolved solids.