Lack of a comprehensive treatise on the biology of fishes has prompted this humble piece of work leading to Essentials of Fish Biology. This is an ideal textbook of fish biology which will serve as valuable work for undergraduates and graduates looking for a comprehensive source on a wide variety of topics in fish Biology. Inclusion of diseases in fishes could be an added advantage for the readers. It is believed that the book will be an invaluable tool for students researchers and practitioners working in the fields of fish biology.