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HAVBRUK2-Stort program for havbruksforskning

Interpreting the cortisol stress response in fish welfare research

Alternative title: Tolkning av cortisolresponsen på stress i fiskevelferdsforskning

Awarded: NOK 2.2 mill.

Common aquaculture practices like transportation and vaccination can be stressful to farmed fish. Stressed fish grow more slowly and are more likely to get sick. A high level of fish welfare is important ethically, but will also improve productivity, profit and reputation of fish farms. To identify stressful farming practices, good tools to measure stress in the fish are important. When the fish experience stressful conditions, like being netted out of the water, the brain will signal production of the stress hormone cortisol. Cortisol makes the fish more aroused and vigilant and makes sure the fish has enough energy available to fight or escape. Levels of cortisol in the fish?s blood increase within minutes of the fish experiencing stress, and stay elevated until the stressful experience ends. Therefore taking a blood sample of the fish and measuring the amount of cortisol in the blood can be a good way to see how stressed the fish is. However, if the cortisol response is on for too long, cortisol changes the area in the brain responsible for signalling cortisol release. It becomes less sensitive and less cortisol is released the next time the fish gets stressed. This is called negative feedback, and the consequence is that a single measurement of cortisol from the blood isn?t always reliable in telling how stressed a fish is. The CortFish project aims to develop a new biological test to identify chronically stressed fish. This will be done by characterizing the negative feedback mechanism of cortisol in the important aquaculture species Atlantic salmon. Then a new test will be based on this knowledge and modelled on medical tests for humans experiencing high levels of cortisol due to disease. The test will be validated in fish farms to see how well it works in predicting welfare, disease resistance and growth. If successful, this new test will be a valuable tool in aquaculture and fish welfare research.


The steroid stress hormone cortisol is a much used indicator of stress in fish, and is widely applied as a marker for welfare in aquaculture. Elevated cortisol levels in fish are associated with stress, growth retardation, immunosuppression and mortality, and may such represent a physiological response to the full width of challenges met by farmed fish. The value of single time point measurements of cortisol for assessing stress level has recently been challenged as there is need to account for diurnal and seasonal variations, as well as environmental and genetic factors. Preliminary data show that chronically stressed fish expected to have high cortisol responses, instead display an attenuation of the cortisol response. It is in such cases not possible to determine if a reduced endocrine stress response is due to robustness and high coping ability, or represents a potentially serious welfare challenge in the form of lack of an appropriate response caused by long-term over-activation of the HPI axis. The CortFish project will further elucidate the mechanisms of negative feedback on cortisol release in chronically stressed Atlantic salmon. I will demonstrate how an established tool from human medicine, the dexamethasone feedback test, can be used to resolve ambiguous cases of attenuated cortisol response. Additionally, the HPI axis activity may predict long-term performance and mortality in aquaculture, a relationship that CortFish will investigate further. To ensure fish health and welfare, we need reliable tools and markers to identify compromised animals and aquaculture practices, and CortFish will meet this requirement.

Funding scheme:

HAVBRUK2-Stort program for havbruksforskning