The environment impacts on the physiology and psychology of animals in a wide variety of ways. If we can develop an understanding of how different environmental factors affect different processes we may be able to predict these changes and avoid or moderate deleterious events and the resultant changes in fish health and disease resistance. In this review, advances in the understanding of environmental impacts were identified in relation to specific areas of immune function. The trends, where they can be identified, showed that increases in light, temperature, salinity, oxygen, pH or particulates results in a general increase in immune function.