Brown trout (Salmo trutta) eggs with eyed embryos

On Tuesday 8 December Kalle Filipsson, RivEM PhD student, will present his work on how elevated temperatures and predator presence during egg incubation affect development and behaviour of brown trout. The seminar starts at 13:15 and will be streamed live on Zoom. Contact Kalle ( if you are interested in attending the seminar, and he will send you a link.

Karl Filipsson, Eva Bergman, Larry Greenberg, Martin Österling, Johan Watz and Ann Erlandsson recently published the paper “Temperature and predator-mediated regulation of plasma cortisol and brain gene expression in juvenile brown trout (Salmo trutta)” in the journal Frontiers in Zoology.

In this study, we tested how temperature and the presence of a cold-water adapted predatory fish (burbot, Lota lota) affected primary stress responses (i.e. cortisol and mRNA levels of stress-related genes) in juvenile brown trout (Salmo trutta). We found that trout had elevated cortisol levels in the presence of burbot, and that stress-related gene expressions varied a lot with temperature. In addition, we found that the predator-induced effects on mRNA levels were temperature dependent for some of the genes. This, together with the directly temperature-mediated effects that we observed in our study, suggest that warming winters can have major impact on primary stress responses in overwintering salmonids, for instance in encounters with predators.

In the abstract of the paper, we wrote that:

“Temperature affects many aspects of performance in poikilotherms, including how prey respond when encountering predators. Studies of anti-predator responses in fish mainly have focused on behaviour, whereas physiological responses regulated through the hypothalamic-pituitary-interrenal axis have received little attention. We examined plasma cortisol and mRNA levels of stress-related genes in juvenile brown trout (Salmo trutta) at 3 and 8 °C in the presence and absence of a piscivorous fish (burbot, Lota lota).

One of the experimental aquaria used for the study.

A redundancy analysis revealed that both water temperature and the presence of the predator explained a significant amount of the observed variation in cortisol and mRNA levels (11.4 and 2.8%, respectively). Trout had higher cortisol levels in the presence than in the absence of the predator. Analyses of individual gene expressions revealed that trout had significantly higher mRNA levels for 11 of the 16 examined genes at 3 than at 8 °C, and for one gene (retinol-binding protein 1), mRNA levels were higher in the presence than in the absence of the predator. Moreover, we found interaction effects between temperature and predator presence for two genes that code for serotonin and glucocorticoid receptors.

We extracted mRNA from the forebrain (telencephalon) of the trout. The picture shows a trout brain after dissection, where the telencephalon is the two upper lobes.

Our results suggest that piscivorous fish elicit primary stress responses in juvenile salmonids and that some of these responses may be temperature dependent. In addition, this study emphasizes the strong temperature dependence of primary stress responses in poikilotherms, with possible implications for a warming climate.”

You can read the paper for free on the journal website, as the paper is published open access through funding provided by Karlstad University.

On Friday 13 March, Kalle Filipsson, NRRV PhD-student, will defend his (my) licentiate thesis. The thesis has the title ”From behaviour to genes: anti-predator responses of brown trout (Salmo trutta) under winter conditions”. The defense will be held in room 1B309 (Sjöströmsalen) at Karlstad University, and starts at 10:00. Stefán Óli Steingrímsson, Professor at Hólar University, Iceland, is the opponent. The defense is open for everyone who wishes to attend.

Kalle’s licentiate thesis, nailed to one of the “theses trees” at the Biology Department at Karlstad University.
Three juvenile brown trout (Salmo trutta), doing trout stuff in a stream flume at Karlstad University.

On Tuesday 25 February, Kalle Filipsson, RivEM PhD student, will give a seminar entitled ”From behaviour to genes: anti-predator responses of brown trout under winter conditions”. The seminar starts at 13.15 in room 5F416, everyone who wants to is welcome to attend the seminar.

This seminar is a practice seminar in preparation for Kalle’s (my) licentiate defense, which will be held Friday 13 March at 10:00. More information about the licentiate seminar will be provided closer to the defense.

Juvenile brown trout (Salmo trutta). Photo: Karl Filipsson
A burbot (Lota lota) in a stream flume at Karlstad University. Photo: Karl Filipsson

Burbot, Lota lota

On Tuesday 3 April 2018, Karl Filipsson, PhD student at Karlstad University, will give a talk titled “The effects of temperature and light conditions during winter on antipredator responses of juvenile brown trout against burbot”. The seminar will start at 13:15 in room 5F416 at Karlstad University. Everyone is welcome to attend the seminar.


Karl Filipsson, PhD-student at Karlstad University.

Karl Filipsson has recently joined the NRRV-research group. Here he writes about his previous work and what he intends to do as a PhD-student at Karlstad University:

My name is Karl Filipsson and I recently started my PhD in the River Ecology and Management Research Group (NRRV) at Karlstad University, where I am going to study the winter ecology of stream fishes in relation to climate change. I have a master’s degree in biology from the University of Gothenburg, with focus on aquatic and evolutionary ecology. Although I have a broad interest in fish ecology and behavior, I have developed a special interest for fish inhabiting streams. In my master project I studied the effect of parasitic freshwater pearl mussel (Margaritifera margaritifera) larvae on brown trout (Salmo trutta). The project mainly examined behavioral responses in the host fish, but growth and cardiorespiratory parameters were measured as well.

In my PhD I will use an experimental approach to look at the consequences of warmer winters on predator-prey interactions and early life-history performance in stream fishes. I will use brown trout and burbot (Lota lota) as model species. River ecosystems and associated fish populations have a significant role in providing important ecosystem services. Therefore, it is of great importance to acquire knowledge on the winter ecology of stream fishes under climate change. Hopefully, results from this project will not only elucidate how stream fishes are adapted to winter conditions and respond to environmental change, but will also provide information for stakeholders and decision makers on how to manage fish populations and stream ecosystems in a future influenced by global climate change.

In addition to research, I have a great interest in scientific outreach. I have previously been working at the science center Universeum in Gothenburg and as scuba diving guide, and I am very keen on taking on the challenge to communicate research to the broader public and to be teaching in higher education.”

Some of Karls previous work on the interaction between juvenile brown trout and frehswater pearl mussel larvae is published in the scientific articles Encystment of parasitic freshwater pearl mussel (Margaritifera margaritifera) larvae coincides with increased metabolic rate and haematocrit in juvenile brown trout (Salmo trutta) and Heavy loads of parasitic freshwater pearl mussel (Margaritifera margaritifera L.) larvae impair foraging, activity and dominance performance in juvenile brown trout (Salmo trutta L.).


The paper “Winter sheltering by juvenile brown trout (Salmo trutta) – effects of stream wood and an instream ectothermic predator” by Åsa Enefalk, Johan Watz, Larry Greenberg and Eva Bergman was recently published in the journal Freshwater Biology. The paper presents a study on the sheltering behavior of the juvenile trout in presence and absence of burbot and bundles of stream food. In the abstract the authors write:

  1. In boreal streams, juvenile salmonids spend substantial amounts of time sheltering in the streambed and in stream wood, presumably as a means of protection against the physical environment and from terrestrial endothermic predators. Relatively little is known about sheltering by salmonids in response to instream ectothermic predators.
  2. We tested the effects of burbot (Lota lota) on the winter sheltering behaviour of PIT-tagged 0+ brown trout (Salmo trutta) in daylight and darkness. Sheltering in the streambed by trout was studied in the presence and absence of fine wood bundles.
  3. We found that the use of streambed and fine wood was lower in darkness than in daylight. Availability of fine wood significantly decreased sheltering in the streambed, and this effect was more pronounced in daylight than in darkness. The presence of a burbot significantly decreased sheltering in the streambed, had no effect on use of fine wood and resulted in a higher number of exposed trout.
  4. Our results indicate that juvenile brown trout decrease streambed sheltering in response to a burrowing, ectothermic predator.

Read the paper here. If you don’t have access to the journal’s content, email any of the authors.

Tomorrow, December 15, Åsa Enefalk, PhD Student at Karlstad University, will give a seminar titled ”Fine wood and burbot – do they affect trout sheltering at low water temperatures?”

The seminar will be given at 13:15 in room 5F416 on Karlstad University. Everyone is welcome to attend!