Abstract
Analysis of the primary freshwater fish faunas of the four principal areas of Southeast Asia shows that 1) the fauna of the Irrawaddy-Salwin basins, while including endemic forms, is as a whole intermediate between th faunas of India and the Indosinian district, 2) the faunas of the Greater Sunda Islands and the Mekong-Chao Phya basins have a close resemblance, but rather many mainland genera do not occur on the islands and some endemic forms are found in each the area, and 3) the fauna of the Song-Koi basin is similar to that of southern China and distinct from those of other part of Southeast Asia. In the cyprinid fishes there are several groups which differ in the evolutionary history and pattern of dispersal. Their ancestral stock may have been well established geographically in main part of Southeast Asia during the early Tertiary. The sharp boundary separating the Chinese and the Indo-Indosinian subregions suggests the former existence of a certain effective and long-lasting barrier extending from the Bay of Tonkin nearly to Yunnan.
