This book will provide clear knowledge of how to conserve different endangered, threatened, rare and vulnerable, etc. fish species in freshwater ecosystems. In view of the developing different nature of stressed conditions in the various aquatic ecosystem, the fish population of many species has been declining year after year. As a result, the fish diversity of many more species has been greatly reduced in water. In the present book, various aspects of fish biology have been discussed with results along with tables and figures. Simultaneously, different observations of fish biology are explained in a biological way by which it would be convenient for a biologist to develop strategies for the conservation of a fish species so that the fish diversity of an ecosystem can be restored.