Correlations between fish assemblage structure and environmental variables of the Seti Gandaki River Basin, Nepal

This paper addresses the relationship between fish and environmental variables from the Seti Gandaki River Pokhara, Nepal. The water bodies previously had higher abundance and distribution of fishes, which are declining probably due to deterioration of abiotic characteristics and degradation of habitat. Five study sites were: three along the main channel and two along the tributaries. Water sampling was conducted fortnightly and fish sampling was done monthly. Altogether 30 species of fishes belonging to 5 orders, 9 families and 24 genera were recorded. The redundancy analysis (RDA) revealed significant correlations between fish assemblage and environmental variables. The first two axes accounted for 44.15% of the variation of which RDA1 explained 30.32% and correlated with conductivity, pH, dissolved oxygen, free carbon dioxide, ortho-phosphate, nitrite and silicates; while RDA2 explained 13.83% and correlated with depth, width, discharge and nitrates. Likewise, RDA1 revealed a gradient from species that require more oxygenated waters of upstream sites (Schizothorax richardsonii, Pseudecheneis eddsi, Naziritor chelynoides, Garra annandalei, Schistura rupecula and Lepidocephalichthys guntea) to less oxygenated urban and downstream sites (Puntius sophore, Pethia conchonius, Barilius bendelisis, Barilius vagra, Garra gotyla, Mastacembelus armatus and Channa orientalis). RDA2 revealed the gradient from species inhabiting urban and downstream sites to upstream sites.