Regulation and function of the stress response in fish

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Fish have evolved various physiological mechanisms to cope with natural environmental stressors enabling them to live in a broad range of habitats as well as to radiate into the most diverse group of species among vertebrates. However, human activities leading to habitat degradation and accelerated climate change are reducing the predictability of the environment, and increasing the frequency and magnitude of environmental stressors. In fish, the hypothalamic-pituitary-interrenal (HPI) axis is activated in response to stressors and in the short term plays a pivotal role in orchestrating a broad and coordinated suite of physiological responses that promote survival. In contrast, chronic activation of the HPI axis and cortisol production can lead to a variety of negative consequences and exposure to stressors during critical developmental windows can influence the responses of fish to subsequent environmental challenges. Although fine-balance regulation of the stress response is essential to health and survival, relatively little is known about the specific mechanisms that regulate the HPI axis in a context-specific manner. Research in my lab is focused on understanding the mechanisms responsible for the regulation of the HPI axis and the means by which early environmental stressors affect the responses of fish to subsequent challenges. Taking advantage of the unique attributes of zebrafish as a developmental model and of rainbow trout to integrate molecular mechanisms with whole-organism outcomes, the goals of this proposal are to 1) determine whether the neuropeptide corticotropin-releasing factor (CRF) has cytoprotective actions in zebrafish embryos and adult hearts following exposure to stressors; 2) assess the relationships between cortisol, neurogenesis, cognitive performance and environmental complexity in adult zebrafish; 3) establish whether environmental stressors and cortisol during development have persistent effects on the stress response and spatial learning abilities of adult zebrafish; and 4) determine the role of the cytokine leptin in the regulation of the HPI axis in hypoxic rainbow trout. Overall, the proposal addresses novel questions about the impact of environmental stressors in shaping the phenotype of adult fish, the cytoprotective roles of stress mediators during development and adulthood, and the function of cytokines in regulating the HPI axis. As such, this research will further our understanding of the short and long term impact of environmental stressors, broaden our knowledge of the specific mechanisms that mediate the stress response, and enhance our ability to minimize or counteract the negative impact of stress in animals. This research also has important applications for animal welfare, the aquaculture industry and for agencies involved in the assessment of anthropogenic activities on wild fish populations.