Importance of freshwater as a shelter of aquatic biodiversity and the increasing threats to it are briefly discussed. Eastern Himalaya, a biogeographic region, which is now considered aquatic biodiversity hotspot is defined. The rich freshwater biodiversity, particularly of fish by vicariance evolution in the region is related to the palaeo-drainage basin evolution as result of tectonic movements, upheaval of the great Himalayas and Indo-Myanmar ranges. A note on the purpose of the book is also given. Freshwater ecosystems, which hold about 0.01% of world’s water, are the most endangered ecosystems in the world and the declines in biodiversity in it are far greater than in the most affected terrestrial ecosystems. The reasons are the environmental change and human activities. Freshwaters house several plants and animals of which 40% is global fish diversity and 25% is global vertebrate diversity.
Freshwater Fishes of the Eastern Himalayas, 2021, pp 1-13,