Species Composition and Altitudinal Distribution of Fish in Upper Walawe River Basin in Sri Lanka

The fish assemblage and limnological factors at 154 sites of upper Walawe river basin, Sri Lanka were studied from April 1999 to March 2001. Out of the 26 species of fish recorded, 24 were indigenous and two were exotic. Of the indigenous species, six were endemic. Indigenous fish species were not present at an elevation above 1500 m MSL. The exotic species, Onchorynchus mykiss inhabits tributaries of Belihul Oya only in the Horton Plains at an elevation of 1900 m MSL. Garra ceylonensis is the most widely distributed endemic fish species. It was present at an elevation of even 1500 m MSL. Since there are no geomorphic impassable barriers, the altitudinal distribution of these fishes may be dependent on water temperature.