We present potential threats to biodiversity in the rivers of East and Southeast Asia, especially focusing on freshwater fishes. The threats would be mainly categorized four factors; 1) habitat loss, 2) degradation of water quality, 3) damming, and 4) overfishing.

1) Variation of microhabitat such as pool-riffle unit is destroyed by river development. Natural riverbanks, which are decreased by artificial embankment, are also important for feeding and spawning of fishes. Decay of mangroves and floodforest as fish habitats may also affect the diversity.

2) Change of land use due to recent economic development has changed the water quality, degreasing fish diversity and biomass.

3) Damming would negatively affect migratory fishes, as well as large-scale damming itself is habitat destruction. Intake weirs decrease the riffle environment, making stream mostly the pool environment.

4) Overfishing and poaching of rare species would be also a problem, while the evaluation is difficult.

We will show these threats with original/secondary data obtained from rivers in Japan, China, Vietnam, Cambodia, Laos, Thai and Malaysia.