Identifying and managing maladaptive physiological responses to aquaculture stressors

Abstract No matter how well designed, commercially viable aquaculture systems invariably impose some level of stress on fish, in part due to a combination of husbandry and/or environmental factors that may be unavoidable. Most of the knowledge and understanding of the stress response in fish comes from laboratory studies in which aquaculture-related stressors are examined in either or both cultured and wild individuals. While such controlled studies have provided important information about stress in fish, they can only partially mimic the intensive rearing environments of aquaculture systems and there is little information of the stress response under commercial conditions. The stress response can vary with species, developmental stage, sex, genetics, environmental and physical factors, season, and duration of exposure. In addition, successful aquaculture requires an understanding of the response to both acute and chronic stressors, and whether these responses are adaptive or maladaptive. In commercial systems, fish are exposed to unavoidable and unpredictable stressors that in some instances can happen simultaneously throughout the production cycle. However, we know little about the effects of stressors on adaptive or maladaptive physiological and behavioral responses under commercial conditions. For the benefit of fish welfare and the sustainable development of the aquaculture industry, there is a need to investigate the effects of chronic exposure to stressors on fish growth, development, immune system, reproduction and survival under commercial culture conditions. When conducting farm-level studies, methodological aspects must be carefully considered. Factors such as environmental conditions, position and location of experimental units, sample number and frequency, season, species, genetic background, developmental stage, and exposure to multiple stressors should be considered as they can affect all levels of the organisms' responses. In addition to the above, there clearly is a need to develop reliable and consistent indicators of stress in aquaculture systems that would indicate not only adaptability but also deleterious effects. With the advances in tracking, visual, and molecular tools, there is an opportunity to integrate the different levels of response (from cell to whole organism) to increase our understanding of the stress response, and perhaps facilitate its translation into better welfare, health and productivity in aquaculture systems.