Man has been playing a key role in shaping the environment with most of his activities directed towards its overall degradation. The aquatic ecosystems, which remained balanced and unaffected till the early days of civilization, get rapidly deteriorated due to population explosion, unmindful disposal of sewage and mushroom growth of industries. Billions of gallons of waste water from cities, housing settlements, industries and agricultural fields are thrown into watercourses everyday. Consequently, the ecology of water and ethology of biota existing therein have been greatly threatened. So, in order to focus the importance of ecology and ethology of aquatic biota, the present book has been brought out. The present book is a unique compilation of 90 articles contributed by eminent authors with different backgrounds, which will act as a key-board in opening new vista in the field of aquatic environment. With its application oriented and interdisciplinary approach, the book would be immensely useful to everyone dealing with aquatic environment, such as University teachers, environmental scientists, academicians, technocrats, politicians, researchers and post graduate students.