Louis Addo (Ph.D. Student at Karlstad University)

Louis Addo (Doctoral Student), Mahboobeh Hajiesmaeli (Post-doctoral Researcher), John Piccolo (Professor) and John Watz (Associate Professor in Biology) all from the River Ecology and Management Research Group RivEM, Department of Environmental and Life Sciences at Karlstad University have recently published a paper entitled “Growth and mortality of sympatric Atlantic salmon and brown trout fry in fluctuating and stable flows” with the journal Ecology of Freshwater Fish.

In their paper, they explore the potential effects of hydropeaking or short-term regulated rivers on the growth and mortality of sympatric Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) at the fry life stage.

This paper is open-access and can be found at https://onlinelibrary.wiley.com/doi/epdf/10.1111/eff.12685

The Scanian river Vramsån (Fig 1) has been a stage for RivEM research before, but not with the wide range of methods that Ph.D. candidate Sebastian, visiting intern Hanna Paikert and Ph.D. candidate Jacqueline tried out in May this year!

Vramsån has long been used for hydropower purposes but is now in the process of being restored to a more natural flow regime. It is one of seven rivers of interest to the LIFE Connects conservation project, which aims to improve their ecosystem functions and ecosystem services. Under six years the project will work with removal of hydropower plants and dams, create fauna passages and improve migration paths at barriers. The project also works on innovative passage solutions that enables both hydropower production and fish migration as well as riverbed restorations to gain more natural habitats and improved water quality. The goal is to improve survival and production of threatened fish species such as Atlantic salmon and European eel as well as the endangered mussel species Freshwater pearl mussel and Thick-shelled river mussel. Research and information efforts linked to river restorations within the project will constitute an important part of the project, that you can read more about on https://lifeconnects.se/!

With that in mind, the first goal of this research adventure was to collect fish and mussel specimens for a study on the impact of light pollution on the host-parasite relationship of the endangered Thick-shelled river mussel (Unio crassus) and its host the common Eurasian minnow (Phoxinus phoxinus).  

This incredibly endangered, and ecologically significant mussel has rapidly diminishing populations, something that LIFE Connects is trying to change. While many people don’t think much of these simple bivalves they play a key role in keeping environmental conditions stable. By filtering suspended particulates from the water column large populations of mussels can keep water cleaner, a benefit to both fish and humans. When they need to poop, the majority goes into the surrounding sediment, fertilizing it and improving both benthic fauna communities and plant growth. Together, these help fortify fish and bird populations. Not only does the increased plant growth provide habitat but the increase in benthic fauna provides more food sources as a large part of benthic fauna communities are comprised of the larval forms of terrestrial insects.

One of the main ways we try to prevent the Thick-shelled river mussel from going extinct is to increase the chances of their reproductive success, a complex cycle and significant factor in their population decline. These mussels are partial parasites on fish, with this extra step making their reproduction rate be quite a bit slower than other freshwater bivalves. We can help by forcefully infecting host fish with mussel larvae and keeping them safe for a large part of the reproductive cycle before releasing them back into the wild. As such the first part of this study was to go electrofishing for fish to use as hosts in for the mussels to be reintroduced, primarily minnows and trout. The trout got to stay in the river (Fig 2) while the minnows were destined to come back to KAU to be used in some experiments. More on that in another blog post

Re-naturalizing the flow regime of a river doesn’t just affect the fish and their ecological functions in it, but other processes as well. Dispersal is one of these processes, and is thought to be important for the composition of all plant communities, including those that we find in-water and in the riparian zone. There are many ways in which plants disperse (Fig 3), and a large part of Jacqueline’s Ph.D. project focuses on dispersal via water. Most of this dispersal is in the direction of the water flow, but many people overlook a tiny component: the animals in the water that swim in the opposite direction! These animals can carry seeds on their outsides or, via foraging, in their bodies. This relatively little-studied function called endozoochory builds on the thought that animals spread other species by eating them in one place and pooping them out elsewhere.

A second goal of this week was finding out whether this pathway is an important route for riparian vegetation in Vramsån. The fish that we were catching thus had a double function: not only will they be used for mussel larva infestation, but we collected their poop to compare the seeds therein with seeds and vegetation in other parts of the ecosystem (Fig 4).

Which other parts, you ask? Well, of course, fish stomachs are not the only place where you find seeds – far from that! Given that there are so many ways in which plants disperse, we planned a comparison of the seed composition in different parts of the ecosystem. So, equipped with self-built traps to filter seeds from the water (Fig. a), to catch seeds from the air (Fig. b) and loads of boxes to sample riparian litter, riparian soil and aquatic soil, we went to work!

It took some hours to get everything in place, but while Seb will spend his spring infesting his fish in Karlstad University’s (KAUs) aquarium facility, Hanna and Jacqueline are running a germination study to see which species pop up in the samples of the different ecosystem parts. After two weeks in KAUs plant growing room, over 200 seeds of at least 10 different species have germinated across the different sample types. We are giving the samples a few more weeks to see what else poops up before we’re going to try and sniff out if there’s anything interesting in there!

Hi! My name is Mahboobeh Hajiesmaeili. I joined the RivEM research group for the second time, as a Visiting Research Project Assistant in December 2020. I worked in this research group in the year 2019, too. I have a PhD in River Engineering from Tarbiat Modares University (TMU), Tehran, Iran. My research interests center around the ecological modeling and river habitat assessment for freshwater fish and benthic invertebrates using individual-based/agent-based modelling (IBM/ABM) and bioenergetics approach, as well as physical habitat simulation models. I’m currently the chair of Ecohydraulics committee of the Iranian Hydraulic Association (https://iha.ir/ecohydraulics/).

During my M.Sc. project my main challenge was to introduce and enhance understanding of the multidisciplinary science of “Ecohydraulics” in Iran, which was completely new in my country. I used PHABSIM (Physical HABitat SIMulation) model for my M.Sc. thesis to investigate the effects of flow hydraulic parameters on rainbow trout. This study was one of the first habitat simulation studies about the interaction between ecology and hydraulics in Iran.

As a result of my interest in ecohydraulics and freshwater aquatic ecosystems, I was interested to focus on more developed habitat selection models for my PhD project and I focused on inSTREAM (individual-based Stream Trout Research and Environmental Assessment Model), which is one of the most important individual-based habitat selection models, and one of the main purposes of my research was to modify inSTREAM in its feeding and growth component to include more about how fish feed and how it depends on spatial variation in invertebrates. Given that the primary food sources of brown trout in my study area (Elarm River in Lar National Park, Iran) were benthic invertebrates and also due to the lack of considering these types of feeding organisms and their associated feeding strategy in other bioenergetics models presented so far, development of a new version of inSTREAM by considering hydraulic parameters affecting biomass of benthic invertebrates was the most important innovation of my PhD research. I was so lucky that one of my PhD supervisors was Steve Railsback, who is the main developer of inSTREAM and helped me a lot to improve my knowledge in individual-based modeling.

Starting in the left top corner, clockwise: Elarm River which is a fabulous trout reproduction habitat with plenty of suitable spawning grounds in Lar National Park (Iran); Identified benthic invertebrates in my study site; Collecting benthic invertebrate samples using a Surber sampler in Elarm River); Identifying benthic invertebrates in the laboratory; Me and my field studies team work in my PhD project
Mahboobehs first book, written from the results of both my M.Sc. and Ph.D. studies with collaboration of my PhD supervisor and my M.Sc. thesis advisor (in Persian)

Immediately after receiving my PhD degree, I was successfully accepted by John Piccolo to work in the KK Eflows project within the RivEM-research group at Karlstad University for a short term employment as a visiting researcher. My work was mostly focused on preparing inSTREAM input data using QGIS for Blankaström (Emån) and also downstream part of Gullspång River (Stora and Lilla Åråsforsen).

Mahboobeh and Kristine Lund Bjørnås  (former RivEM Lic-student) in the Day of the Salmon at Fortum in Gullspång, 2019

As a project assistant in our ongoing project I will focus on ecological and individual-based modelling of Atlantic salmon and brown trout habitat using inSTREAM in the lower part of the Gullspång River (Stora and Lilla Åråsforsen) under hyropeaking conditions. I will collaborate with John Piccolo, Johan Watz, and Louis Addo.

One of my favorite activities during my free time is drawing portraits. Considering that my research work is such that I should spend too much time on my computer, drawing and art help me to relax 🙂 

Some of Mahboobehs drawings

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 (karl.filipsson@kau.se) if you are interested in attending the seminar, and he will send you a link.

Our former PhD student Anna Hagelin and several other researchers, amongst them Larry Greenberg, Olle Calles and Eva Bergman, recently published a new paper in the Canadian Journal of Fisheries and Aquatic Sciences.

They examined fishway passage of landlocked Atlantic salmon in River Klarälven, Sweden and brown trout in River Gudbrandslågen, Norway, and the influence of prior experience on passage success in 2012 and 2013. Fishway trap efficiency varied from 18 to 88% and was influenced by river discharge. Most salmon (81%) entered the fishway trap on days without spill, and salmon moved from the turbine area to the spill zone when there was spill, with small individuals showing a stronger reaction than large fish. Analysis of fish with and without prior trap experience showed that a higher percentage of the “naïve” fish (70% of salmon and 43% of the trout) entered the fishway traps than the “experienced” ones (25% of the salmon and 15 % of the trout). Delays for fish that entered the trap ranged from 3-70 days for salmon and 2-47 days for trout.

The paper is not publicly accessible, but can be requested via ResearchGate.

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 Thursday 26 March, Kristine Lund Bjørnås, NRRV PhD-student, will defend her licentiate thesis “Modeling Atlantic salmon and brown trout responses to river habitat alteration”. The defense starts at 10:00. Asbjørn Vøllestad, Professor at the University of Oslo, is the opponent for Kristine’s defense.

Kristine’s defense will be held as an online meeting on Zoom (a video communication system commonly used by universities). You should be able to follow Kristine’s defense using this link:


The defense will also be streamed live on a bigscreen in lecture hall 1B309 (Sjöströmsalen) at Karlstad University, and everyone is welcome to watch the defense from the lecture hall. Please note that Kristine and the opponent will not be in the lecture hall.

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 10 March, Kristine Lund Bjørnås, PhD student at Karlstad University, will give a seminar entitled “Modeling Atlantic salmon and brown trout responses to river habitat alteration”. 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 Kristine’s licentiate defense, which will be held Thursday 26 March at 10:00. More information about the licentiate seminar will be provided closer to the defense.

Kristine Lund Bjørnås and Niclas Carlsson taking point measurements of the physical habitat in Gullspångsforsen.

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