The present study of two years of fish composition data from 7 sites in the Tunga River, Western Ghats, Karnataka, India, were examined for relationships with environmental variables using a multivariate approach including Principle Component Analysis, Jaccard Similarity co-efficient and diversity index packages. 67 fish species were recorded representing 6 orders, 16 families and 40 genera and the family cyprinidae was found to be dominant which contributed 36.73 to 96.64%. The study found that there was a quite difference in fish species richness and abundance in selected sampling sites and species richness varied longitudinally in relation to environmental parameters. The fish species richness and abundance were correlated with water quality parameters and it was shown that pH, turbidity and conductivity influence and structure the fish composition in this river system. Therefore, the study would be helpful in suggesting and adopting the sustainable and effective measures to conserve the fish diversity of this river.