ABSTRACT
This chapter reviews the effect that salinity may have on the fish immune responses, following by the importance and magnitude of the osmoregulatory hormones to finally deal with the endocrine-osmoregulation-immunity interactions in fish whose osmotic balance has been altered. The innate and adaptive immune responses that they display share many similarities with the mammalian immune system. The fish immune response is intended to eradicate an invading agent, the antigen. The fish immune system—like that of other vertebrates—consists of physical barriers and immune organs. Salinity is one of the most important environmental factors for aquatic organisms. In teleost fish, environmental salinity fluctuations trigger the osmoregulatory response to compensate for such changes. Once the pathogen has entered the fish, the host elicits an inflammatory response involving humoral and cellular components of the innate immune response. Major Histocompatibility Complexes (MCH) are highly polymorphic cell surface proteins consisting of MCH class I and class II glycoproteins.
