A juvenile brown trout in the experimental flume.

Johan Watz, postdoc at Karlstad University, recently published the scientific article “Stress responses of juvenile brown trout under winter conditions in a laboratory stream” in the journal Hydrobiologia. In the abstract he writes: “Winter can be a challenging period for fish in northern temperate rivers and streams, particularly in those that are channelized, structurally simple or regulated by, for instance, hydropower. In these systems, dynamic sub-surface ice formation commonly occurs and stable periods with ice cover may be short. Under these adverse conditions, access to shelters has been shown to be an important factor that influences overwinter survival, and exclusion from shelters by anchor ice may cause stress. Here, stress responses of juvenile brown trout under simulated winter conditions in an artificial stream were studied. Trout were subjected to three treatments in which the trout (1) were excluded from an instream wood shelter, simulating the effects of anchor ice, (2) had access to the shelter or (3) had surface ice cover in addition to the shelter. There was a positive correlation between ventilation frequency and plasma cortisol concentration. Trout without access to shelter had 30% higher ventilation frequency than trout with instream shelter and surface ice, but no differences in cortisol concentration or stress colour were found between the treatments. River regulation that reduces surface ice and increases anchor ice formation may lead to increased stress and consequently reduce overwinter survival rates.”. 

Access the paper here: Stress responses of juvenile brown trout under winter conditions in a laboratory stream.

Tomorrow (Tuesday), February 28, David Aldvén from the University of Gothenburg and Vattenfall AB, will give a seminar titled ”Downstream migration of anadromous brown trout”. David Aldvén finished his PhD with a thesis titled ”Migration in anadromous brown trout”. The frame of his thesis is available online here.

The seminar will be given at 13:30 in room 5F416 on Karlstad University. Everyone is welcome to attend!

Freshwater pearl mussels.

The paper “Heavy loads of parasitic freshwater pearl mussel (Margaritifera margaritifera L.) larvae impair foraging, activity and dominance performance in juvenile brown trout (Salmo trutta L.)”  by Karl Filipsson, Tina Petersson, Johan Höjesjö, John Piccolo, Joacim Näslund, Niklas Wengström, Martin Österling was recently published in Ecology of Freshwater Fish. In the abstract the authors write:

“The life cycle of the endangered freshwater pearl mussel (Margaritifera margaritifera) includes a parasitic larval phase (glochidia) on the gills of a salmonid host. Glochidia encystment has been shown to affect both swimming ability and prey capture success of brown trout (Salmo trutta), which suggests possible fitness consequences for host fish. To further investigate the relationship between glochidia encystment and behavioural parameters in brown trout, pairs (n = 14) of wild-caught trout (infested vs. uninfested) were allowed to drift feed in large stream aquaria and foraging success, activity, agonistic behaviour and fish coloration were observed. No differences were found between infested and uninfested fish except for in coloration, where infested fish were significantly darker than uninfested fish. Glochidia load per fish varied from one to several hundred glochidia, however, and high loads had significant effects on foraging, activity and behaviour. Trout with high glochidia loads captured less prey, were less active and showed more subordinate behaviour than did fish with lower loads. Heavy glochidia loads therefore may negatively influence host fitness due to reduced competitive ability. These findings have implications not only for management of mussel populations in the streams, but also for captive breeding programmes which perhaps should avoid high infestation rates. Thus, low levels of infestation on host fish which do not affect trout behaviour but maintains mussel populations may be optimal in these cases.”

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

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.

Today Åsa Enefalk successfully defended her PhD-thesis ”Fine stream wood – Effects on drift and brown trout (Salmo trutta) growth and behavior”. Theopponent was Stanley Gregory from Oregon State University whereas the grading committee consisted of Teppo Vehanen, Natural Resources Institute Finland, Ingrid Ahnesjö, Uppsala University, and Erik Pettersson, Swedish University of Agriculture.

Åsa Enefalk’s supervisors during her PhD were Eva Bergman, Anders NIlsson and Raimo Neergaard

The thesis is available here. Contact Åsa Enefalk for individual papers.

Dr. Åsa Enefalk defending her thesis.

On Friday, 21 September, Stan Gregory from Oregon State University will give a seminar titled “Population dynamics of coastal cutthroat trout and Pacific giant salamanders in old-growth forest and second-growth forest reaches of a Cascade Mountain stream in Oregon, USA”. The seminar will be given at 15:00 in room 5F416 at Karlstad University.

Spawning cutthroat trout (photo: Yellowstone National Park).

Stan Gregory is in Karlstad as the opponent at Åsa Enfalks PhD defense. Åsa Enefalk will defend her thesis ”Fine stream wood – Effects on drift and brown trout (Salmo trutta) growth and behavior”  at 10:15 on the same day (Friday 21 September) in Nyquistsalen (room 9C 203) at Karlstad Univeristy.

Everyone is welcome to attend both events!

CANCELED SEMINAR

On Tuesdag, 20 September, David Aldvén from the University of Gothenburg, was to give a seminar titled ”Downstream migration of anadromous brown trout”. David Aldvén recently finished his PhD with a thesis titled “Migration in anadromous brown trout”. The frame of his thesis is available online here.

The seminar has been CANCELED.

Åsa Enefalk spikar traditionsenligt upp sin avhandling på väggen vid universitetets entré.

Idag spikade Åsa Enefalk, doktorand vid Karlstads Universitet, sin doktorsavhandling “Fine stream wood – Effects on drift and brown trout (Salmo trutta) growth and behavior”. Åsa kommer att försvara sin avhandling fredagen den 23 september kl. 10:15 i Nyqvistsalen, 9C 203. Alla är välkomna!

Stanley Gregory från Oregon State University kommer att vara opponent medan betygskommittén består av Teppo Vehanen, Natural Resources Institute Finland, Ingrid Ahnesjö, Uppsala universitet, och Erik Pettersson, SLU.

Imorgon, tisdagen den 23 Augusti, kommer Åsa Enefalk, doktorand vid Karlstads Universitet, ge ett seminarium med titeln “Fine stream wood – effects on drift and brown trout (Salmo trutta) growth and behaviour”. Seminariet ges klockan 13:30 i sal 5F416 på Karlstads universitet. Alla är välkomna!

En ung öring gömmer sig bland fin död ved (foto: Anders Tedeholm)

On Tuesday, June 7, Joacim Näslund from the University of Gothenburg, will give a seminar titled ”The pace of life of brown trout: linking growth and survival with animal personality”.

In the abstract for the seminar, Joacim writes: “The Pace-of-Life syndrome (POLS) hypothesis suggests that different individuals within a species have different combinations of physiological, behavioural and life-history traits, which are linked together. Typically, researchers have classified individuals into a few, typically two, major categories:  proactive (or bold) and reactive (or shy). Following the POLS proactive individuals are for instance more active and bold to support a faster metabolism and a higher growth rate, they have a lower stress response, and they typically have a higher risk of mortality. The reactive individuals have the opposite traits. In the seminar, I will discuss the POLS hypothesis in the light of several recent experiments on wild brown trout. I will show that the POLS is not as straight forward and intuitive as presented in conceptual papers on the topic. For instance, while several traits are linked together in a syndrome in the brown trout, the predictions from POLS are not confirmed by empirical data. As an example, during the early juvenile stage more active fish tend to have a higher probability of survival, despite a higher presumed exposure to predators and competitors. A potential explanation, relating to the behavioural ecology of the juvenile brown trout will be presented. Furthermore, I will show that the probability for survival for different POLS categories of trout likely changes during their ontogeny.”

The seminar will be given at 13:30 in room 5F416 on Karlstad University. Everyone is welcome to attend!