Abstract: The present paper introduces the process of the Burma - Malaya Geoblock movement northward and the historical environmental changes in the Gaoligong Mountains. The biological effect of the Burma -Malaya Geoblock movement on the fish fauna in the region has been studied based on current data of fish oc-curred in the drainage system of the Salween River and Irrawaddy River within the region: 1. The two drainage systems have fish fauna from both the Palaearctic region and Oriental regions. 2. The line demark-ing the transition between Asiatic fish fauna to the south and the Tibetan Plateau fish fauna to the north is at approximately 26°N latitude with neither fish from the north passing the line to the south nor those from the south to the north. 3. The Gaoligong Mountains is a center of species differentiation for many fish taxa. The endemism of fish in the region reaches as high as 53 of the total fish fauna. 4. The origin of fish fauna in the Gaoligong Mountains may be from the tropics and may be from the temperate area of Palaearctic region. The authors believe that the family Sisoridae has a tropical origin but its individual genera and species have different origins. Most genera in the Sisoridae originated from the tropics while Glyproarwenum and its related genera probably originated from Tibet.

Key words: Gaoligong Mountains