91̽»¨

Thermal acclimation in ectothermic animals is the process of adjusting biochemistry, physiology, morphology, and behaviour to altered body temperature. Often, these modifications serve to counter the direct effects of temperature on biological rates and macromolecular functioning. For example, we have shown that domesticated zebrafish (Danio rerio) lines have lost plasticity compared with wild zebrafish (). 

We additionally study the dynamics and mechanisms of thermal acclimation in many marine fish and invertebrate species. Our recent book chapter covers some of the main mechanisms behind thermal acclimation ().

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We use various strategies to investigate thermal adaptation. We have conducted two very large multi-year artificial selection experiments. These experiments on wild-caught zebrafish spanned up to eight generations and tens of thousands of individual fish. 

Our first evolution experiment, led by , tested if acute upper thermal tolerance (estimated by CTmax) and the plasticity of it (thermal acclimation) can evolve. We found that thermal tolerance did indeed evolve over only a seven generations, but the rate of evolution was very slow and the plasticity did not increase ( ). 

To understand what physiological mechanisms had changed from the artificial selection experiment, one large project led by  measured many performance and life-history traits. We found that contrary to predictions, oxygen transport and thermal sensitivity of metabolic rates were not altered. Likewise, it was unexpected that the thermal window increased through both higher CTmax and lower CTmin.

A recently finished large artificial selection experiment co-led by  and  tested if thermal performance curves can diverge through adaptation to warmer or cooler water. The performance trait chosen was growth rate at optimal, cold, and warm temperatures. Results will be published soon. 

The upper thermal limits of fishes have been studied for a very long time (e.g., Davy J. Some observations on the vitality of fishes as tested by increase in temperature. Rep Brit Ass Adv Sci 32: 125, 1862). Despite this, our understanding of the physiological mechanisms determining the upper limits is limited. Our recent review led by () covers this topic in detail. 

We have studied if the brain is a main organ limiting the thermal tolerance of fish. In transgenic zebrafish larvae, we found that it was a gradual decline in brain function when approaching thermal limits that appeared to lead to loss of response, and this decline was oxygen limited (). 

We have also studied the  and found species and life-stage differences. Projects led by  and  have shown very rapid thermal acclimation (also called heat hardening) that can occur already three hours after a heat shock. 

The role of oxygen in limiting thermal tolerance and performance of ectothermic water breathers (the OCLTT hypothesis) has been a long-standing debate in ecophysiology (, , , , ). Together with a large international team, we recently tested if hyperoxia can increase acute upper thermal tolerance across many fish and crustacean species from several continents. We found that most species were oxygen-indifferent at normoxia, contrary to what the OCLTT hypothesis predicted.

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The performance of fishes can be modulated by temperature, and the decline in performance at higher temperatures is a main focus of the group. We have suggested that the decline in growth during warming may be explained by reduced appetite due to a voluntary protection of the aerobic scope after a meal ().

How swim performance and aerobic scope is affected by warming and how this is modulated by water oxygen level is under investigation by . 

Most of our work is on whole animal physiology but one project led by Leon Pfeuffer uses organ baths and another project led by  is using cell lines. For example, we are investigating how thermal tolerance and acclimation are controlled at a cellular level. More to come. 

For some research questions, modifying a genetic pathway can be a direct way of investigating its role. This is now quite accessible through CRISPR modifications. We knocked out the heat shock response system in zebrafish to investigate its role in thermal tolerance and thermal acclimation. This work is ongoing, led by .

Early life stages of fishes have been suggested in a disputed meta-analysis to be the most vulnerable to the impacts of warming. We are therefore investigating if this pattern holds true through empirical studies on fish embryos. We use various ramping and static thermal exposures in many fish species in projects led by collaborator  and postdoc . One excellent tool used by Lorena Silva is the thermal gradient table (Figure) that maintains ten different temperatures and five replicates per temperature.

Elevated water CO2 levels have been suggested to cause dramatic behavioural effects such as a reversal of predator avoidance into strong attraction to predators. In a large multi-year replication effort, we showed those effects to be non-replicable (). 

In a meta-analysis, we found that the effect sizes of the impacts of CO2 on fish behaviour have been steadily declining over the past decade, from extremely large to currently close to zero in a process called the decline effect ( ;  ). 

Additionally, some experimental results using choice flumes have been found to be fabricated ( ) and papers have been retracted, partly due to our work. This suggests we should be sceptical of the claims of many early papers, as we explain in this comprehensive book chapter on .

Aquatic hypoxia is a growing problem in both freshwater systems and the oceans, and warming surface waters can increase stratification further. We investigate how fish performance is impacted by hypoxia. In a collaboration with the University in Bergen, we are testing how coral reef fishes cope with fluctuating oxygen levels at night on Moorea ().

Hyperoxia, when oxygen levels are above 100% saturation, can occur during daytime when waters warm and photosynthesis is high, with largely unknown effects on fishes. We use hyperoxic water in various experiments to test if hyperoxia can alleviate oxygen limitation and therefore increase thermal tolerance or thermal performance in fishes. 

Our group is interested in how to ensure our work is solid and replicable. Over the past decade, we have witnessed several instances of poor science and outright fraud. These experiences have made us highly motivated to improve the scientific practices in our field. 

Read about our work exposing scientific misconduct and data fabrication in fish ecology and microplastics () , fish ecology and ocean acidification (; ). Many papers that we have reported remain published without retractions or expressions of concern, as no university has decided to investigate them. 

As experimental biologists, we find that specific methods and tools that we need don’t exist. Therefore, we have published various method development articles and best-practices guideline reviews:

• Machine vision for automated landmarking, led by . 
• Thermal tolerance measurements in fish, best-practices review. 
• Regulation of water oxygen levels, led by . 
• Thermal tolerance measurements in embryos, led by . 
• Two-current choice flumes. 
• Thermal tolerance measurements in zebrafish. 
• Two-current choice flumes, best-practices review. 
• Aquatic respirometry, best-practices review. 

, PhD candidate
Signe investigates intestinal function in salmonids. Jutfelt is co-supervisor, Rolf Erik Olsen is main supervisor.

, Researcher
Zara is an ecologist with a background in mainly aquatic animal behaviour. Her current topics are thermal adaptation and climate change vulnerability across life stages in fish. Zara is now a Researcher and P.I. at the University 91̽»¨, Kristineberg Center. 

, PhD 
Anna is studying the mechanisms of thermal tolerance with a focus on how phenotypic traits vary with selection for thermal tolerance, and the role of the central nervous system and cardiac capacity during heat challenges. Anna is currently a postdoc at the University of Copenhagen.

, PhD Candidate
Mette is studying the behavioural thermal plasticity of zebrafish, which includes the within- and between individual variation in behaviour expressed at various temperatures, and how these behaviours vary together (covariance). 

, PhD 
Hanna is investigating the physiological mechanisms underlying the ‘temperature size rule’ phenomenon, whereby aquatic organisms like fishes cannot grow as large in warmer waters. Co-supervised with  at Deakin University. 

, Postdoc and Researcher
Josefins project investigated the effects of ocean acidification and other environmental stressors on fish behaviour and reproduction. She currently holds a permanent position as researcher at the Department of Aquatic Resources, The Swedish University of Agricultural 91̽»¨s, Sweden. 

, Marie-Skłodowska Curie Postdoc
Jeffs project took a comparative approach to study the effects of multiple global change stressors on the behaviour of fishes and invertebrates by integrating empirical laboratory studies with synthesis science (meta-analyses). He now has a permanent position as Research Scientist at the Aquaculture and Coastal Ecosystems Section, Fisheries and Oceans Canada, Canada.

Rachael’s PhD project investigated acclimation and adaptation potential to temperature in fish. She used artificial selection in zebrafish and showed that. Rachael is currently a postdoc at the University of Bergen.

, PhD (Co-supervised by Jutfelt)
Archana is a PhD candidate investigating behavior, neurophysiology and stress in fish. Jutfelt is co-supervisor, Florence Kermen is main supervisor.

(Co-supervised by Jutfelt)
Laura's PhD project explored how elevated levels of dissolved CO2 (ocean acidification) and low concentrations of the pharmaceutical oxazepam affect the neurophysiology and behaviour of fish. Main supervisor was Svante Winberg. Laura is currently a Post-Doc at the Swedish University of Agricultural 91̽»¨s, Uppsala, Sweden.

(Co-supervised by Jutfelt)
Ariannas PhD project revolved around the GABA system in fish. Arianna is currently a Senior research engineer at the Department of Medical Biochemistry and Microbiology at Uppsala University, Sweden.

, PhD 
In his PhD project (2012-2017), Andreas studied the relationship between cardiovascular performance and thermal tolerance in fish (Co-supervised by Jutfelt, main supervisor Erik Sandblom). Andreas is currently working as a researcher at the University 91̽»¨.

, PhD 
PhD in 2013 (Co-supervised by Jutfelt, main supervisor Kristina Snuttan Sundell).

Miriam Dørum, Research technician
Miriam was head of the animal facilities, keeping our zebrafish lines thriving. She was also involved in experiments and data analysis.

Adriana de Aguiar Martins, Research technician
Adriana was head of the animal facilities, keeping our zebrafish lines thriving. She was also involved in experiments and data analysis.

​Jonas Arntsen, MSc 
Jonas tested how selecting for higher and lower critical thermal maxima in zebrafish affected their thermal preference.

Mons Lien, MSc student
Mons is a 2nd year master student, writing his thesis on swim speed and metabolic rate in zebrafish.

, MSc 
Anders did a two-year MSc project on the effects of oxygen and temperature on growth and appetite in fish.

Sondre Kristenstuen, MSc 
Sondre did a two-years project on how oxygen and temperature affect growth and appetite in fish, with focus on activity level and swim performance.

Marie Reiersen, MSc 
Marie is a LUR MSc student doing a project on how thermal acclimation and oxygen affect thermal tolerance (CTmax) in fish.

Sandra Steen, MSc 
Sandra studied the effects of high intensity interval training in humans. Jutfelt was co-supervisor,  was main supervisor.

, MSc student
Eirik did a two-year project on the thermal performance and thermal tolerance of wild-caught zebrafish, in relation to environmental factors. Parts of that work is . Eirik did his PhD with Craig Primmer at the University of Helsinki, Finland. 

, MSc student
Kristin investigated how VO2 affects cardiovascular risk in older adult humans. Jutfelt was co-supervisor, main supervisor .

Hanne Margrethe Hildrum, MSc student
Hanne did a one-year MSc project on thermal tolerance using CTmax and CTmintests, combined with results from behaviour experiments, on zebrafish. 

Tine Brusevold, MSc student
Tine did a MSc project studying differences in plasticity in behavioural traits in wild caught zebrafish lines exposed to different thermal treatments. Co supervised with .

Gunnar Dresler, MSc student
Gunnar did a two-year project on the thermal physiology and plasticity of wild-caught zebrafish.

, MSc student
Leon did a MSc project on how ocean acidification may affect . Leon has recently finished his PhD in evolutionary ecology of invasive fishes under Lotta Kvarmeno at the University 91̽»¨. He is now working as an assistant professor on marine invasive species.

, MSc student
Maria did a project investigating if cod are affected by elevated CO2 levels resulting in two papers ,.

Roman Motyka
Roman did a MSc project on how ocean acidification may temperate fishes.

Violetta García Muñoz (Spain)
Violetta is an Erasmus student from the University of Valencia who helped with various zebrafish experiments in 2021-2022 during an internship in our lab.

Nathalie Folliard (France)
Nathalie conducted an experiment testing how heart rate in various species of crabs is affected by temperature. 2021-2022.

Margarita Villalonga Roca de Togores (Spain)
Marga is a Spanish Erasmus student who conducted various zebrafish experiments during 2019.

Mireia Silvestre (Spain)
Mireia is a Spanish Erasmus student who conducted various zebrafish experiments during 2018.

Marc Vendrell (Spain)
Marc is a Spanish Erasmus student who conducted various zebrafish experiments during 2017.

Daphne Cortese
Daphne, together with Amelia Munson, ran a large experiment on temperature and fish behaviour in our lab.

Amelia Munson
Amelia, together with Daphne Cortese, ran a large experiment on temperature and fish behaviour in our lab. 

Brenna Stanford
Brenna stayed with our lab in Trondheim while finishing up her PhD at the University of Calgary.

Jay is a fish physiologist studying the impacts of warming and parasites on fish. Jay is collaborating on several projects and has been running experiments in our lab during 2022.

Daniel Sadler
Daniel is a fish ecologist who studies fish genomics, climate change, and all things fish. He ran a long temperature and hypoxia experiment at NTNU during 2022.

Dr Joanna Miest
Joanna collaborates on a project on fish olfaction and chemical ecology, and on a project testing how thermal evolutionary history affects thermal acclimation capacity.

Adam collaborated on a project for improving two-current choice flume research.

Davide tested how thermal acclimation affects swim performance in zebrafish.

Adrian collaborates on a project testing how thermal evolutionary history affects thermal acclimation capacity, with a focus on gene expression patterns.