Novel methods to evaluate fish response to stress
Farmed fish are submitted to many stressors that have an important impact on their health and can even lead to their premature death. The COPEWELL project has tried to help fish farmers cope with this issue by developing methods that will allow them to better understand how fish experience their surrounding environment.
The EU COPEWELL (A new integrative framework for the study of fish welfare based on the concepts of allostasis, appraisal and coping styles) project was completed in December 2015, although the project team intends to keep publishing papers in 2016. Their main objective, which consisted in providing a better understanding of the physiology, biology and behaviour of fish, their underpinning mechanisms and the way in which coping styles emerge, has largely been achieved.
Dr Tore Kristiansen coordinated the project for the Institute of Marine Research in Norway. He elaborates on how its results deepen our knowledge of the development of the brain function, behaviour and stress response in farmed fish, and how it provides tools for a better assessment of fish welfare and, last but not least, hints at solutions to improve this welfare.
Why is it important to know more about how fish experience their world?
Because this is what fish welfare is about! We want to study quality of life as experienced by the fish. Was it a nice experience or not? How good or bad was it? There is still a debate on whether fish have conscious experiences, and this is something we wanted to investigate.
What was the methodology you used in this investigation?
The challenge was to develop methods that could answer our questions. Especially for farmed species, the necessary sizes and number of experimental arenas were demanding. We developed several methods and used the small zebrafish as a model organism, and then scaled some of these methods up to European seabass, Gilthead seabream and Atlantic salmon.
An example of a method used under COPEWELL is the Conditioned Place Preference Test, where the fish are exposed to rewarding or aversive conditions in different areas of a fish tank. The areas where they experienced the assumed good or bad stimuli were marked with different background patterns. If the fish experience the conditions as aversive, they will later associate this pattern with the aversive experience and avoid this area and thereby show their subjective experience. The opposite will happen if the stimuli were experienced as positive. In addition to fish behaviour, we also looked at gene expression of so-called immediate early genes and monoamines in the brain, in order to study which areas of the brain were affected.
Why did you choose to extend this research to different species?
It is important to recognise that a fish is not just a fish. We have around 30 000 species of fish in the world, and there is probably a much larger difference between various fish species than between a bat and an elephant. Comparing salmon and sea bass is like comparing a tiger and a dog, or a pig and horse. Even within the same species we found different coping styles or 'personalities': fish behaved differently and had different neurophysiological and genomic responses to the same experiences.
What have you learned with regards to the consequences of poor fish welfare?
In many of the experiments we could see that the fish had a remarkable ability to adapt to stressful conditions as long as they could cope with the given challenges. A central concept in the project has been that of 'allostasis' as an alternative model to the old homeostasis model.
Instead of conditions with as few stressors as possible, the fish should be submitted to stressors they can successfully cope with. The brain will reward successful behaviour and such reward is what creates pleasurable experiences and good welfare. Of course, all organisms have limited resources: too many challenges and stressors will lead to wear and tear of the body, and finally a breakdown of overall physiological functioning.
Other than that, what would you say are the most important outcomes of the project?
In the COPEWELL project we have maybe for the first time in aquaculture studied how experiences early in life affect later development, behaviour, brain neurochemistry and stress responses. We have shown that we can modify how fish react to stressors by creating predictable conditions.
According to the allostasis model, the fish (or human) regulate their bodily functions according to predicted demand. If the conditions are predictable—meaning that the fish has experienced a similar situation before and can estimate what is coming, it will give more appropriate stress responses instead of overreacting to the stimuli and spending more resources than necessary on stress handling.
At last we now have a better understanding of the underpinning mechanisms in the brain, but here most of the map is filled with blank areas. We are still in the early stages of fish brain neuroscience.
How can aquaculture benefit from your findings?
Handling stress is a large source of mortality in farmed fish. If we train the fish to handle stressors like, for example, crowding or pumping in a better way, this should lead to both a better survival rate and growth. Also fish need training and education!
Our results have shown that fish have different coping styles and personalities that are more or less fit for aquaculture conditions. This should be further studied and implemented in the breeding programmes.
The project has already come to an end but you already said that more papers would be coming in 2016. Can you tell us more about this ongoing work?
By now I think we have published 25 papers related to the project, and more than 20 papers are in the pipeline. We hope most of them will be accepted. I must also mention that we have four PhDs who have already defended their thesis and a few more will finish it this year.