Fish biology refers to the study of the group of animals that have gills and are aquatic craniates. It includes animals like lampreys, bony fish, hagfish, cartilaginous fish, etc. As fishes are an essential food product for animals as well as human beings, it becomes very important to understand their biology. Therefore, fish biology includes the examination of their digestion, circulation, respiration, excretion, scales, etc. This book provides comprehensive insights into the field of fish biology. It picks up individual branches and explains their need and contribution in the context of the growth of this discipline. Those with an interest in fish biology would find this textbook helpful.