ABSTRACT
The purpose of Chapter 6 is to provide a general overview of our current understanding of how xenobiotics target the immune system of teleostean fish and explore new frontiers toward understanding mechanisms of action and how these mechanisms may address the question of ecotoxicological consequences. There are over 20,000 different species of fishes, so it is impossible to draw simple or generalized conclusions about the immunobiology or immunotoxicology of all fish, because the differences between immune systems of major groups and between species within each group are substantial. Herein, we focused on those species of fish commonly used in research relevant to aquaculture, environmental health, and as models for human and veterinary biomedicine. Although seemingly primitive in comparison with mammals, the immune systems of fish are highly evolved to meet the demands of the environment in which they live. Surrounded by water of optimal temperature, fish exist in a relatively stable environment. Water, however, is teaming with microorganisms, some of which are pathogenic, while others may share a commensal or mutualistic relationship with the host, and they may form part of the microbiotic community (microbiome) on the epithelial surfaces of fish. The immune system must distinguish between these relationships. In addition, the water column contains dissolved inorganic and organic substances, some of which may affect immunocompetence. The importance of integument as an immune organ is maintained throughout the evolution of vertebrates, culminating in an extremely complex component of immunity and homeostasis in all modern vertebrates.
