During the past two decades, fish endocrinology has witnessed exciting developments due to our increased knowledge at all levels of biological organizations, including molecular biology, cell biology, physiology and behavior. New insights into development, neurobiology, immunology and molecular genetics closely correlated with classical aspects of endocrinology and represent important contributions to our knowledge on regulatory processes of vertebrates, including fish. The purpose of this book is to overview major advances in numerous research areas of fish endocrinology. Most of the chapters not only review and discuss the state-of-the-art in the respective field, but also show perspectives of future research. The book will be of interest to scientists involved in basic fish research, comparative endocrinology, fisheries and aquaculture as well as for students of fish biology.