The greatest complexity of the immune response is shown by vertebrates which are endowed with innate and acquired immunity. Immunological studies performed mostly in mammals have been the reference for studies in other vertebrates. The study of immunological fish defenses has advanced considerably in recent decades. This has been due to the key status of fish in terms of the evolution of acquired immunity and due to the rapid expansion of aquaculture over this period, wherein disease control is of prime concern. Most of the chapters not only review the current advances on fish immune...