The present study reveals the presence of 37 fish species belonging 5 order, 14 family and 28 genera. Highest number of species belong to order cypriniformes (22 species) followed by order Perciformes (8 species), order siluriformes (4 species) order synbranchiformes (2 species) and cypriniformes (1 species). Population of fish species is more less in plain regions particularly, Barilius bendelisis (Ngawa) Neolissochilus hexagonolepis (Ngara), Acanthophthalmus pangia (Nganap) Labeo angra (Ngaton), Acanthobitis botia (Ngatup) Macrognathus aculeatus (Ngaril), Mystus bleekeri (Ngasep) etc. Main reason may be attributed to the uncontrolled fishing by using electronic device and construction of mini-dams across the river. The factors which influence the distribution and diversity of fishes in the study area have been discussed.