Bengt Erik Höglund

• Staven, Fredrik; Imsland, Albert; Gesto, Manuel; Soares, Marta C.; Iversen, Nina S. & Meland, Ine [Show all 10 contributors for this article] (2026). Effects of dietary L-tryptophan enrichment on stress response, growth and survival in lumpfish (Cyclopterus lumpus) following sea transfer. Aquaculture. ISSN 0044-8486. 618. doi: 10.1016/j.aquaculture.2026.743813. Full text in Research Archive Show summary

  L-tryptophan (TRP), the precursor to serotonin (5-HT), modulates stress responsiveness and social behaviour in vertebrates. In cleaner fish such as lumpfish (Cyclopterus lumpus), these traits are integral to sea lice control in Atlantic salmon (Salmo salar) farming. We tested whether a TRP-enriched diet attenuates the stress response during commercial sea transfer and affects early cohabitation performance. Lumpfish were fed a control (5.2 g kg−1) or TRP-enriched diet (24 g kg−1, 4.6× control TRP) for 7 d, fasted for 2 d before transport, and then fed for 14 d after deployment in commercial net pens. Post-transfer stress was assessed using plasma cortisol concentrations. Telencephalic 5-HT neurochemistry was quantified as [5-HT], its metabolite 5-hydroxyindoleacetic acid [5-HIAA], and 5-HIAA/5-HT. Performance was evaluated based on growth, stomach content, and survival. TRP feeding increased 5-HIAA/5-HT after the pre-transfer phase, indicating increased serotonergic turnover, and reduced post-transport plasma cortisol, consistent with reduced HPI-axis reactivity. During 16 d of salmon cohabitation, TRP-fed fish showed a higher proportion of empty stomachs and slightly reduced growth, while cumulative survival did not differ between treatments. By the end of cohabitation, telencephalic 5-HIAA had converged back to similar means, while 5-HT remained significantly elevated in the TRP group. Overall, short-term dietary TRP enrichment reduced acute handling and transport stress in lumpfish without compromising survival, but prolonged exposure was associated with reduced feeding and growth. Dietary TRP enrichment thus appears promising as a pre-conditioning strategy to enhance lumpfish robustness during critical husbandry stages, although potential trade-offs with feeding motivation, growth, and cleaning behaviour require further study.

• Sørensen, Christina; Vas, Judit; Folkedal, Ole; Bui, Samantha; Remen, Mette & Gunnes, Mikkel [Show all 11 contributors for this article] (2026). Regional brain serotonergic activity as an indicator of chronic stress and compromised welfare in fish. Frontiers in Endocrinology. 17, p. 1–12. doi: 10.3389/fendo.2026.1736618. Full text in Research Archive Show summary

  Background: Chronic stress in aquaculture poses major challenges to fish welfare, health, and productivity. Detecting compromised welfare early requires validated biomarkers that link operational welfare indicators (OWIs) to underlying neuroendocrine states, including allostatic load and stress coping capacity. The central serotonergic system is a promising candidate for such validation, given its conserved role in stress regulation across vertebrates. Methods: We sampled 40 Atlantic salmon ( Salmo salar ) from research-scale sea cages spanning a wide range of welfare states under production-relevant conditions. Fish were exposed to acute crowding during routine rearing operations immediately prior to sampling. Plasma cortisol was measured, along with serotonin (5-HT) concentration and turnover, proxied by 5-hydroxyindoleacetic acid (5-HIAA) and the 5-HIAA/5-HT ratio, in the brain stem and telencephalon. Associations among 5-HTergic variables, welfare indicators (OWI sum, scale loss, condition factor), and acute stress metrics (crowding time, cortisol) were analysed using principal component analysis (PCA), multivariate analysis of variance (MANOVA), and post hoc linear models. Results: Brain stem 5-HT concentration and turnover were consistently associated with welfare-related indicators and loaded strongly with these variables in multivariate space, indicating sensitivity to cumulative stress and compromised welfare. In contrast, telencephalic 5-HT turnover aligned primarily with acute stress metrics rather than welfare state. MANOVA and post hoc analyses confirmed these region-specific associations. A significant interaction for telencephalic 5-HIAA revealed that fish in poorer welfare states exhibited a blunted 5-HTergic response to acute stress compared with individuals in better welfare condition, consistent with reduced stress responsiveness under chronic strain. Conclusion: Our findings demonstrate a clear regional dissociation in central 5-HTergic stress processing in Atlantic salmon: brain stem 5-HT activity reflects chronic stress burden and welfare state, whereas telencephalic 5-HT turnover reflects acute stress reactivity conditional on baseline welfare. These results support the use of region-specific 5-HTergic measures as biologically grounded markers distinguishing chronic welfare compromise from functional acute stress responses in aquaculture, while emphasizing caution when interpreting acute stress reactivity in chronically stressed individuals.

• Höglund, Erik; Johansen, Kurt; Ulset, Silje Marie; Sannes, Elise; Haraldstad, Tormod & Johansen, Ida Beitnes [Show all 9 contributors for this article] (2026). Exploring the links between swimming performance, glucocorticoid profiles, behavioral types and cardiac morphology in migrating Atlantic salmon (Salmo salar) smolts. Scientific Reports. 16. doi: 10.1038/s41598-026-35402-y. Full text in Research Archive Show summary

  It has been become increasingly clear that swimming performance is crucial for the migratory success of wild Atlantic salmon (Salmo salar) smolts, yet the associated traits remain largely unexplored. In this study, smolts were caught during their downstream migration to the sea and were categorized as strong or poor swimmers based on their time to fatigue in a swimming test. Behavioral profiles were characterized through a confinement and novelty test, and relationships to cardiac morphology and glucocorticoid profiles were investigated. Strong swimmers increased activity over time in the confinement test, while poor swimmers showed the opposite trend, indicating differences in boldness. There were no differences in plasma cortisol in groups of fish with contrasting swimming performance. Still, strong swimmers had higher cortisone levels 24 h after the swim test, suggesting a protective mechanism against elevated cortisol in this group. No differences in heart morphology were found between the groups. In addition, acoustic telemetry revealed a trend toward lower survival rates for strong swimmers in predator-rich environments. Overall, our results highlight a link between glucocorticoid profiles, boldness and swimming capacity in Atlantic salmon smolts. Further studies are needed to confirm the observed survival patterns and to better understand how predator pressure may shape the fitness consequences of these traits in migrating smolts.

• Staven, Fredrik; Gesto, Manuel; Soares, Marta C.; Iversen, Nina Skorstad; Staven, Andreas R. & Egeland, Torvald B. [Show all 13 contributors for this article] (2025). License to chill: Environmental enrichment for post-vaccination recovery and social training of lumpfish (Cyclopterus lumpus). Aquaculture. ISSN 0044-8486. 609. doi: 10.1016/j.aquaculture.2025.742861. Full text in Research Archive Show summary

  Commercial production of lumpfish (Cyclopterus lumpus) offers a non-invasive, continuous, and environmentally friendly method for controlling sea lice (Lepeophtheirus salmonis and Caligus elongatus) in Atlantic salmon (Salmo salar) farming in the North-Atlantic region. However, rearing lumpfish in barren tanks contrasts with its natural benthic lifestyle, and may impair cognitive development, social interaction and ultimately cleaner behaviour. This study investigated the effect of environmental enrichment (EE) during post-vaccination recovery and after deployment in salmon net pens. A total of 18,000 lumpfish were distributed in six production tanks in a randomised triplicate setup with three tanks for control and three tanks with the combination of plastic shelters and salmon silicone models for seven weeks. The study continued at sea for two months using triplicate net pens, with blinded sampling protocols. Results showed that lumpfish in enriched tanks experienced a significant increase in growth, observed on day 28 post-vaccination and interacted actively with both enrichment types. Vaccination had a significant effect on brain neurotransmitters and blood cortisol but was not affected by EE. After deployment at sea, net pens with enriched lumpfish showed a trend towards reduced lice counts of adult female lice during first two weeks. However, lice consumption in both control and treatment were remarkably high, with pooled ingestion rates ranging from 30 to 36.7 % in weeks 4 and 8 post-deployment. Welfare assessments indicated good condition and no difference across treatments. These findings suggest that EE may serve as a practical strategy with the potential to mitigate post-vaccination stress, and enhance habituation to shelters and salmon cues, supporting its use as a reinforcing measure before deployment at sea.

• Vindas, Marco; Folkedal, Ole; Aerts, Johan; Øverli, Øyvind; Nilsson, Jonatan & Johansen, Ida Beitnes [Show all 8 contributors for this article] (2025). Chronic stress and the development of a depression-like neuroendocrine profile in Atlantic salmon. Journal of Experimental Biology. ISSN 0022-0949. 228(11). doi: 10.1242/jeb.249862. Full text in Research Archive Show summary

  A subpopulation of aquaculture salmon are characterized by abnormal swimming behavior, growth stunting and anorexia, as well as chronically elevated cortisol and brain serotonergic levels. This profile is associated with a depression-like state (DLS) and these fish are unable to respond to further stressors. Whereas the underlying causes behind this phenomenon remain elusive, the physiological profile strongly suggests that chronic stress plays a significant role in this phenomenon. We subjected Atlantic salmon to a chronic stress regime consisting of incremental increases in environmental CO2 concentrations during the freshwater phase for 68 days. Plasma corticosteroids, brain stem, hypothalamic and telencephalic serotonin concentrations and telencephalic whole transcriptome expression were then assessed under basal and acute stress conditions. We found that fish exposed to increased CO2 were characterized by a long-term increase in cortisol, cortisol+cortisone and serotonin (5-HT) signaling in the brain stem. Furthermore, in response to an acute confinement stressor, the CO2-treated fish increased their levels of cortisol and cortisol+cortisone, and decreased their cortisone/cortisol ratio. But unlike the control fish, they were unable to also respond to confinement by increased 5-HT signaling in the brain stem. In terms of their transcriptional response, post-stress gene regulation in CO2-treated fish was the opposite of that observed in control fish. We believe this profile is an example of allostatic overload, characterized by the inability to cope with stress. This profile is associated with DLS, suggesting that chronic stress may be an important factor leading to the development of the DLS phenotype in salmon.

• Delacroix, Stephanie; Jensen, Tor Nystuen; Tobiesen, August E.Dessen; King, Andrew Luke & Höglund, Erik (2024). Ocean alkalinity enhancement impacts: regrowth of marine microalgae in alkaline mineral concentrations simulating the initial concentrations after ship-based dispersions. Biogeosciences. ISSN 1726-4170. 21(16), p. 3677–3690. doi: 10.5194/bg-21-3677-2024. Full text in Research Archive Show summary

  Increasing the marine carbon dioxide (CO2) absorption capacity by adding alkaline minerals into the world's oceans is a promising marine carbon dioxide removal (mCDR) approach to increase the ocean's CO2 storage potential and mitigate ocean acidification. Still, the biological impacts of dispersion of alkaline minerals need to be evaluated prior to its field deployment, especially the impacts of the initial discharge causing local and temporary extreme alkalinity/pH changes. In this study, the toxicity effect on marine microalgae of two commonly used alkaline minerals, calcium hydroxide (Ca(OH)2) and magnesium hydroxide (Mg(OH)2), was determined by adding the same equivalent molar concentration of hydroxyl ions. Cultures of marine green microalgae Tetraselmis suecica were exposed to Ca(OH)2 or Mg(OH)2, in concentrations mimicking the initial high concentrations following a dispersion scenario from a ship. A short-term exposure with high-alkaline mineral concentration called “dispersion phase” was followed by a dilution step and a “regrowth” phase over 6 d. There was no detectable effect of Mg(OH)2 treatment on algae growth either after the dispersion phase or during the regrowth phase, compared to control treatments. The Ca(OH)2 treatment resulted in very few living algal cells after the dispersion phase, but a similar growth rate was observed during the regrowth phase as was for the Mg(OH)2 and control treatments. Standardized whole effluent toxicity (WET) tests were carried out with a range of Mg(OH)2 concentrations using a sensitive marine diatom, Skeletonema costatum, which confirmed the relatively low toxicity effect of Mg(OH)2. Similar biological effects were observed on natural microalgae assemblages from a local seawater source when applying the same Mg(OH)2 concentration range and exposure time used in the WET tests. The results suggest that Mg(OH)2 is relatively safe compared to Ca(OH)2 with respect to marine microalgae.

• Vindas, Marco; Engdal, Vilde Arntzen; Kavaliauskiene, Simona; Folkedal, Ole; Höglund, Erik & Moyano, Marta [Show all 9 contributors for this article] (2024). Importance of environmental signals for cardiac morphological development in Atlantic salmon. Journal of Experimental Biology. ISSN 0022-0949. 227(20). doi: 10.1242/jeb.247557. Full text in Research Archive Show summary

  The hearts of salmonids display remarkable plasticity, adapting to various environmental factors that influence cardiac function and demand. For instance, in response to cold temperature, the salmonid heart undergoes growth and remodeling to counterbalance the reduced contractile function associated with dropping temperatures. Alongside heart size, the distinct pyramidal shape of the wild salmonid heart is essential for optimal cardiac performance, yet the environmental drivers behind this optimal cardiac morphology remain to be fully understood. Intriguingly, farmed salmonids often have rounded, asymmetrical ventricles and misaligned bulbi from an early age. These deformities are noteworthy given that farmed salmon are often not exposed to natural cues, such as a gradual temperature increase and changing day lengths, during critical developmental stages. In this study, we investigated whether natural environmental conditions during early life stages are pivotal for proper cardiac morphology. Atlantic salmon were raised under simulated natural conditions (low temperature with a natural photoperiod; SimNat) and compared with those reared under simulated farming conditions (SimFarm). Our findings reveal that the ventricle shape and bulbus alignment in SimNat fish closely resemble those of wild salmon, while functional analyses indicate significant differences between SimNat and SimFarm hearts, suggesting diastolic dysfunction and higher cardiac workload in SimFarm hearts. These findings highlight the profound influence of environmental factors such as water temperature and photoperiod on the structural development of the salmonid heart, underscoring the importance of early environmental conditions for cardiac health.

• Höglund, Erik; Loland, Lifen Zhou; Høgberget, Rolf; Skov, Peter Vilhelm & Velle, Gaute (2024). No additional stress of sublethal gas supersaturation in a landlocked population of Atlantic salmon (Salmo salar) exposed to environmental acidification. Scientific Reports. 14(1). doi: 10.1038/s41598-024-53637-5. Full text in Research Archive Show summary

  The landlocked Atlantic salmon population “bleke” faces extinction due to environmental acidification (EA) and hydropower expansion in the Norwegian river Otra. Despite of restoration, unexpected mortality has been reported for this population, possibly due to gas bubble trauma (GBT) from gas supersaturation (GSS) downstream of hydroelectric plants, or EA induced aluminum toxicity. In this study, we applied the allostasis concept to investigate interactions between EA and GBT. This concept comprises additive effects of stressors, which can lead to allostatic overload. Stress coping mechanisms become maladaptive in such situations, which can be indicated by an inability to mount a proper cortisol response in fish. Fish were exposed to sublethal levels of simulated EA (SEA), GSS (a total gas pressure; TGP; of 110%) or a combination of these stressors for six days. Effects on allostatic load were subsequently investigated by assessing the cortisol response to an acute stress test. SEA increased cortisol responsiveness and GSS induced clinical signs of GBT, but no interacting effects between GSS and SEA were observed. This suggests that that 110% TGP did not have an additive effect on the allostatic load imposed by SEA.

• Calabrese, Sara; Jonassen, Thor Magne; Steigum, Endre; Åsnes, Helga Øen; Imsland, Albert & Saude, Carolina Serra [Show all 8 contributors for this article] (2024). Does sedation with AQUI-S® mitigate transport stress and post transport mortality in ballan wrasse (Labrus bergyltae)? Frontiers in Veterinary Science. 11. doi: 10.3389/fvets.2024.1347062. Full text in Research Archive Show summary

  Ballan wrasse (Labrus bergylta) are commonly used as cleaner fish in salmon farms as a biological treatment to mitigate sea lice infestation. Improved welfare for cleaner fish both during production of these fish and when in sea-cages with salmon is crucial for the industry’s development. A common operational procedure in ballan wrasse production is transporting juveniles from one land-based farm to another for further on-growing. Episodes of increased mortality have been reported after such transportations. In this study, the relationship between transport stress and post-transport mortality at the on-growing facility was examined. It was also investigated if light sedation with AQUI-S® can mitigate stress during transport. Stress was quantified by measuring cortisol release rate to the tank water during transport. This was investigated in 10 commercial live carrier truck transports (6 without AQUI-S® sedation and 4 with sedation during loading and transport). The total time of transport varied between 12 and 21 h. In general, mortality was significantly higher (1.0 ± 0.6% day−1) the first five days post-transport compared to 15–20 days post transport (0.5% day−1). There was also a strong relationship between fish weight at transport and post-transport mortality, where higher mean weight at transport reduced mortality. In contrast to what was expected, AQUI-S® treatment during transport procedures increased cortisol excretion rate, suggesting a stimulating effect of AQUI-S® on the stress axis in ballan wrasse. Considering these results, the value of using AQUI-S® to reduce stress during transport of juvenile ballan wrasse might be questioned. However, there was no relationship between cortisol release rate during transport and post-transport mortality. Furthermore, this study emphasizes that water cortisol measurements can be used as a none-invasive tool for monitoring stress and can be integrated into the welfare evaluation during commercial fish transports.

• Fernandes, Paulo; Steigum, Endre; Höglund, Erik; Rojas-Tirado, Paula Andrea & Åtland, Åse (2024). Hydrogen sulphide dynamics in recirculating aquaculture systems with moving or fixed bed biofilters: A case study in two commercial salmon smolt producing farms in Norway. Aquacultural Engineering. ISSN 0144-8609. 104. doi: 10.1016/j.aquaeng.2024.102392. Full text in Research Archive Show summary

  Sudden mass mortalities of fish reared in recirculating aquaculture systems (RAS) have occurred in recent years. High total dissolved sulphide (H2S + HS- + S2-) levels in the rearing water have been suggested as an underlaying factor for such mass mortalities. However, limited information is available regarding H2S dynamics in commercial aquaculture production facilities. In this case study, we present H2S dynamics in the rearing water of two commercial salmon post-smolt (150–250 g) RAS facilities equipped with different biofilters: one RAS with fixed bed biofilters (fRAS) and the other RAS with moving bed biofilters (mRAS). The farms operated at different water exchange rates and cumulative feed load but were otherwise comparable in terms of biomass and feed loading throughout the monitoring period. Self-calibrating, automatic gas-phase H2S sensors were installed at three locations per farm: after the fish tanks, after the biofilters and after the degassers and operated for a period of approximately 70 days in both farms. H2S was observed at maximum daily average of 0.6 µg/L in all locations monitored in the two RAS facilities and no significant fish mortality was reported during the monitoring period. In the fRAS, H2S concentration dynamics showed that there was a net concentration increase after the fish tanks and after the biofilters, and a net concentration decrease after the degassers. Furthermore, in the fRAS, backwashing of fixed bed biofilter chambers caused a slight increase in H2S after the biofilters. In the mRAS, there was a net positive increase in H2S after the fish tanks, and a net concentration decrease after the biofilters and degassers. Moreover, generally, H2S concentration in RAS seemed to be unrelated to feeding or fish biomass. Thus, this study suggests that the main contributing factors to H2S dynamics in RAS are biofilter design, system, and tank water exchange rates and, and potentially aeration and turbulence within each compartment.

• Höglund, Erik; Folkedal, Ole; Aerts, Johan; Hvas, Malthe; Øverli, Øyvind & Mangor-Jensen, Anders [Show all 9 contributors for this article] (2023). Welfare effects of environmental hypercapnia quantified by indicators based on morphology and allostatic load in Atlantic salmon (Salmo salar). Aquaculture. ISSN 0044-8486. 572. doi: 10.1016/j.aquaculture.2023.739512. Full text in Research Archive Show summary

  Water supply is a limited resource in most salmon hatcheries, which is compensated by reduced water flow and oxygenation. However, reduced water exchange can lead to accumulation of CO2, resulting in environmental hypercapnia, which may have negative impacts on fish welfare. Thus, environmental hypercapnia can be a common welfare problem for salmon in hatcheries, and particularly in recirculating systems (RAS). In this experiment, Atlantic salmon were exposed to chronic environmental hypercapnia during the last 68 days of the freshwater phase, whereupon effects on physiological stress coping mechanisms and morphological welfare indicators were investigated. Effects on stress coping mechanisms were quantified by measuring changes in brain serotonergic chemistry and plasma cortisol at basal levels and in response to a standardized acute stress test. The results show that exposure to elevated CO2 saturation in the water compromised stress responsiveness of brainstem serotonergic activity, altered osmotic homeostasis, and suppressed growth indicating that fish experience allostatic overload. However, no effects on morphological welfare indicators were observed. This accentuates the need for physiological measures, including physiological responses to controlled challenges to activate the stress axis, when investigating the welfare status of fish reared in systems with potential high CO2.

• Höglund, Erik; Fernandes, Paulo; Rojas-Tirado, Paula Andrea; Rundberget, Thomas & Hess-Erga, Ole-Kristian (2022). Assessing Stress Resilience After Smolt Transportation by Waterborne Cortisol and Feeding Behavior in a Commercial Atlantic Salmon (Salmo salar) Grow-Out Recirculating Aquaculture System. Frontiers in Physiology. 12. doi: 10.3389/fphys.2021.771951. Full text in Research Archive Show summary

  Sampling protocols and water quality sensors have been developed to assess fish health and welfare in recirculating aquaculture systems (RASs). Still, the use of fish-based non-invasive welfare indicators, reflecting the physiological state of the fish, is limited in this type of system. Cortisol, the major stress-coping hormone in fish, diffuses through the gills. Consequently, waterborne cortisol is a potential fish-based non-invasive welfare indicator in RAS. However, its use in commercial rearing systems is sparse. In this study, we evaluated water cortisol levels and feeding behavior as welfare indicators of newly inserted smolt in a commercial RAS for harvest size Atlantic salmon. The RAS consisted of two parallel fish rearing raceways, raceways 1 and 2, sharing the same water treatment with common outlets and inlets. The smolts were inserted in raceway 1 while salmon that have been in the system for 6 months or more were kept in raceway 2. The smolt insertion period was 3 days. Samples for water cortisol levels were withdrawn the day before, 1 and 3 days after the smolt insertion period. Smolt insertion resulted in elevated water cortisol concentrations in the entire system, with the highest values in raceway 1, one day after smolt insertion. Estimated cortisol production in newly inserted smolt decreased over time, was similar to what has been reported in salmon adapting to experimental tanks. Feeding behavior indicated that the appetite was not fully resumed in the newly inserted smolts, while the appetite of fish in raceway 2 was unaffected by smolt insertion. These results, obtained in a highly intensive commercial RAS, suggest that waterborne cortisol together with feeding behavior can be used as indicators for adaptive processes associated with stress resilience in farmed fish. Thus, they are promising non-invasive indicators for assessing the impact of potential stressors on fish welfare in this type of rearing system.

• Johansen, Kurt; Olsen, Esben Moland; Haraldstad, Tormod; Arlinghaus, Robert & Höglund, Erik (2022). Digital Data Help Explain Drivers of Angler Satisfaction: An Example from Southern Norway. North American Journal of Fisheries Management. ISSN 0275-5947. 42(5), p. 1165–1172. doi: 10.1002/nafm.10810. Full text in Research Archive Show summary

  We analyzed trip-level self-reports collected by a cell phone app to understand angler satisfaction of fishing for sea trout Salmo trutta (anadromous Brown Trout) in southern Norway. We found no clear support for a positive relationship between trip outcome (catch or no catch) and angler satisfaction level. In the cases where sea trout was caught, however, there was a positive relationship between fish size and angler satisfaction level. A total of 52% of the captured sea trout were voluntarily released, and releases were unrelated to fish size. In conclusion, digital data collected via a cell phone app are useful to reveal patterns of angler behavior and satisfaction.

• Haraldstad, Tormod; Forseth, Torbjørn; Olsen, Esben Moland; Haugen, Thrond Oddvar & Höglund, Erik (2022). Empirical support for sequential imprinting during downstream migration in Atlantic salmon (Salmo salar) smolts. Scientific Reports. 12. doi: 10.1038/s41598-022-17690-2. Full text in Research Archive Show summary

  The precise homing of Atlantic salmon to their natal river and spawning grounds is the foundation for locally adapted genetically differentiated populations across rivers or across river sections. A sequential imprinting hypothesis states that salmon smolts may imprint on environmental clues along the outward migration route and then use this in reverse order to direct the spawning migration later in life. In this study, we provide empirical support for this hypothesis. PIT-tagged wild Atlantic salmon using a 2 km hydropower tunnel as downstream migrating smolts had a 18% (1SW) and 23% (2SW) lower probability of successfully migrating through the parallel river stretch as adult spawners compared to spawners that migrated through the same river stretch as smolts. These findings highlight how a fine-scale riverine migration route may be imprinted in wild Atlantic salmon smolts. From an applied perspective, these results stress the importance of not depriving smolts from parts of their migration route to ensure successful return of adults to their natal spawning grounds.

• Hundal, Bjørg Kristine; Liland, Nina Sylvia; Rosenlund, Grethe; Höglund, Erik; Araujo, Pedro & Stubhaug, Ingunn [Show all 7 contributors for this article] (2021). Increasing the dietary n-6/n-3 ratio alters the hepatic eicosanoid production after acute stress in Atlantic salmon (Salmo salar). Aquaculture. ISSN 0044-8486. 534. doi: 10.1016/j.aquaculture.2020.736272. Full text in Research Archive Show summary

  Earlier studies have indicated that a high inclusion of n-6 fatty acids (FA) in feeds for Atlantic salmon can affect the stress response. To test this hypothesis, Atlantic salmon (Salmo salar) were fed diets containing varying dietary n-6/n-3 FA ratios and different absolute levels of n-6 and n-3 FAs. The fish were divided into two different stress challenge groups, where one group was exposed to three weekly hypoxia challenges for 4 weeks (repeated stress), while one group was left undisturbed. At the end of the experiment, both groups were exposed to an acute stressor (lowering of water level). Thus, effects of the diets on acute stress, repeated stress and the combined effect of these could be investigated. In general, there were few effects of the repeated stress, while fish in all diet groups responded strongly to the acute stress based on several stress markers. Dietary n-6/n-3 ratio did not affect growth, all fish appeared phenotypically healthy, and all groups were able to mount an acute stress response. However, there was an interaction between diet and repeated stress on cortisol response after acute stress, possibly indicating altered hypothalamic-pituitary adrenal axis reactivity in fish fed high n-6/n-3 FA ratio. Hepatic levels of prostaglandin D2 (PGD2) and leukotriene B4 responded differently to acute stress depending on the dietary n-6/n3 FA ratio, indicating an altered acute stress response. Additionally, increasing the dietary n-6/n-3 FA content led to higher levels of PGD2 and PGE2 as well as higher liver triacylglycerol. In summary, the results suggest that increasing the dietary n-6/n-3 FA ratio in salmon feeds can affect the way they respond to stressors in an aquaculture setting, possibly affecting the fish robustness.

• Höglund, Erik; Høgberget, Rolf; Åtland, Åse; Haraldstad, Tormod; Øverli, Øyvind & Vindas, Marco A (2021). Effects of repeated short episodes of environmental acidification on Atlantic salmon (Salmo salar) from a landlocked population. Science of the Total Environment. ISSN 0048-9697. 753. doi: 10.1016/j.scitotenv.2020.141403. Full text in Research Archive Show summary

  Chronic or repeated exposure to environmental contaminants may result in allostatic overload, a physiological situation in which the costs of coping affect long-term survival and reproductive output. Continuous measurements in Otra, the largest river in southern Norway, show the occurrence of repeated 24–48 h episodes of acidification. This work investigates the impact of repeated short acidification episodes on a unique land-locked population of normally anadromous Atlantic salmon (“Bleke”). This was done by recording physiological measures of stress and allostatic load in fish exposed for 7 days to continuous or repeated episodes of simulated environmental acidification or untreated Otra water (controls). A standardized acute stress test was performed after these different exposure regimes, with brain and blood samples taken before (baseline) or after the stress test. Treatment effects on stress coping ability were assessed by neuroendocrine indicators, including telencephalic serotonergic activity and plasma cortisol. Continuous exposure to acidification resulted in increased baseline plasma Cl− and Na+ and elevated baseline plasma cortisol compared to episodic exposed fish. However, both episodic and continuous acidification resulted in similar increase in gill Al, indicating similar impact on gill permeability of these two exposures. This suggests a lower impact on the electrolyte homeostasis in episodic compared to continuous exposure and that this effect not is directly related to the effects of Al complexes binding to the gills. Furthermore, there were no treatment induced differences on stress coping ability, suggesting that episodic exposure to the sublethal concentrations of Al in pH 5.5 in the present study do not result in higher allostatic load than in control or continuous exposed Bleke.

• Haraldstad, Tormod; Haugen, Thrond Oddvar; Olsen, Esben M.; Forseth, Torbjørn & Höglund, Erik (2021). Hydropower-induced selection of behavioural traits in Atlantic salmon (Salmo salar). Scientific Reports. 11. doi: 10.1038/s41598-021-95952-1. Full text in Research Archive Show summary

  Renewable energy projects such as hydropower facilities contribute towards meeting the world`s growing energy demands and urgent need for mitigating climate change. However, such infrastructure has the potential to substantially alter the environment which, in turn, can induce new challenges related to for instance fish migration conditions. As a consequence, local adaptations related to pre-development migration conditions may be affected for influenced populations. To explore selection regimes operating at a river hydropower plant, we monitored Atlantic salmon smolt individuals during their seaward migration. When passing the hydropower plant, the smolts chose between a surface fish passage or a submerged turbine intake. Smolts were scored for behavioural type (basal locomotor activity, net restrain (a measure of escape responses) and willingness to leave a familiar environment) prior to their migration choice, and we found that smolts with high basal activity had higher probability of using the fish passage than the turbine intake. In addition, migration route choice was a partly consistent trait in that fish that had previously passed a hydroelectric facility by using a fish passage rather than the turbine intake were significantly more likely to use it again when faced with the same choice. Higher mortality among turbine migrants could potentially reduce or eliminate particular behaviour types within populations- and the corresponding population genetic diversity that is essential to cope with future environmental challenges.

• Sissener, Nini; Hamre, Kristin; Fjelldal, Per Gunnar; Philip, P. Antony Jesu; Espe, Marit & Miao, L. [Show all 14 contributors for this article] (2021). Can improved nutrition for Atlantic salmon in freshwater increase fish robustness, survival and growth after seawater transfer? Aquaculture. ISSN 0044-8486. 542. doi: 10.1016/j.aquaculture.2021.736852. Full text in Research Archive Show summary

  The loss of fish in the seawater (SW) phase of Atlantic salmon farming is high, and a major proportion of this loss occurs in the period just after SW transfer. In the current study, we hypothesize that improvements made to the diet during the freshwater (FW) stage affect fish growth, survival and robustness later in the SW stage. To test this, salmon parr were fed five experimental diets in FW at 12 °C. In addition to a commercial-like control diet, fish were fed a diet with changed FA composition aimed to be more like the natural feed of salmon in FW, a diet with increased concentrations of selected AA/N-compounds (methionine, lysine, threonine and taurine), a diet with increased concentrations of methionine and certain B-vitamins (folate, B12 and B6) and a final diet combining all of these potential improvements. At the time of SW transfer, the robustness of fish fed the different diets was tested by direct transfer to SW at three different temperatures (8, 12 and 16 °C, without prior acclimation), as well as transfer into open net pens, while fed on a common commercial diet. Growth and proximate composition of the fish did not differ between the diet groups. All diet groups seemed to handle transfer to SW well, and while SW transfer elicited a stress response in the fish, this was not significantly different between diet groups. Fish transferred to SW at 8 °C had higher mortality, reduced mucus layer and increased prevalence of scale loss and wounds, but this applied to all diet groups. Hence, direct transfer to SW at a lower temperature than the fish has been acclimated to cannot be recommended. At the two highest temperatures, there were some differences between the groups in the severity of cataracts. Apart from this, none of the health- or welfare related parameters measured showed any difference between the diet groups, indicating that the control diet was already sufficient.

• Höglund, Erik; Korzan, Wayne; Åtland, Åse; Haraldstad, Tormod; Høgberget, Rolf & Mayer, Ian [Show all 7 contributors for this article] (2020). Neuroendocrine indicators of allostatic load reveal the impact of environmental acidification in fish. Comparative Biochemistry and Physiology - Part C: Toxicology & Pharmacology. ISSN 1532-0456. 229. doi: 10.1016/j.cbpc.2019.108679. Full text in Research Archive Show summary

  When mobilized from surrounding soils and binding to gills at moderately low pH, aluminum (Al) cations can adversely affect fish populations. Furthermore, acidification may lead to allostatic overload, a situation in which the costs of coping with chronic stress affects long-term survival and reproductive output and, ultimately, ecosystem health. The brain's serotonergic system plays a key role in neuroendocrine stress responses and allostatic processes. Here, we explored whether sublethal effects of Al in acidified water affects serotonergic neurochemistry and stress coping ability in a unique land-locked salmon population from Lake Bygelandsfjorden, in southern Norway. Fish were exposed to untreated water with pH 6.5 and 74 μg Al l−1 or acidified (pH 5.5) water with different aluminum concentrations ([Al]; 74–148 μg l−1) for 5–6 days. Afterward, effects on stress coping ability were investigated by analyzing plasma cortisol levels and telencephalic serotonergic neurochemistry before and after a standardized acute stress test. Before the stress test, positive dose-response relationships existed between [Al], serotonergic turnover rate and plasma cortisol. However, in acutely stressed fish, exposure to the highest [Al] resulted in reduced cortisol values compared with those exposed to lower concentrations, while the positive dose-response relationship between Al concentrations and serotonergic turnover rate persisted in baseline conditions. This suggests that fish exposed to the highest Al concentration were unable to mount a proper cortisol response to further acute stress, demonstrating that neuroendocrine indicators of allostatic load can be used to reveal sublethal effects of water acidification—and potentially, the environmental impacts of other factors.

• Johansen, Ida B; Höglund, Erik & Øverli, Øyvind (2020). Individual Variations and Coping Style. In Kristiansen, Tore S; Fernö, Anders; Pavlidis, Michail A & Vis, Hans van de (Ed.), The Welfare of Fish. Springer Nature. ISSN 9783030416751. p. 283–301. doi: 10.1007/978-3-030-41675-1_12. Full text in Research Archive Show summary

  By current definition, animal welfare depends on the subjective experience of cognitive and emotional processes that are engendered as individuals succeed or fail in coping with a dynamically changing environment. A functional and evolutionary approach to emotion holds that adaptive qualities such as duration, severity, controllability, and predictability of stressful stimuli determine whether a particular event or outcome is experienced as rewarding or adverse. For instance, stress-induced behavioral inhibition can be seen as an adaptive strategy during chronic, unpredictable, or uncontrollable conditions that do not merit successful active coping. In teleost fishes, such behavior can be taken to indicate a negative welfare status, since it co-occurs with reduced neural plasticity and neuroendocrine alterations akin to brain remodeling seen in depression-like states in mammals. Active responses such as aggression and active avoidance are on the other hand likely to be adaptive when stressors are mild, predictable, and of short duration. Such conditions, albeit leading to acute activation of physiological stress responses, does not necessarily impair welfare. Thus, individual variation in the threshold for when a challenge becomes inhibiting rather than stimulatory is likely key to the subjective experience of welfare in a given situation. Thresholds for employing active (proactive) and passive (reactive) responses are, however, individually variable, and complex gene–environment interactions affects the occurrence and stability of welfare relevant trait correlations. In this chapter, we will review how key components of a stress coping style (i.e., behavior, physiology, neuroendocrinology, neuronal plasticity, and immunity) are subject to great individual and heritable variation, and further how such specific trait characteristics can influence the welfare of fish. A practical outcome for applied studies in aquaculture is that if one aims to understand and measure welfare in the context of individual variation in coping ability, relevant indicators of central nervous system function must somehow be included. The robustness of available markers of neural plasticity and their sensitivity to stress exposure is not fully resolved, but impaired welfare status is most often recognizable by characteristic behaviors such as reduced activity and feeding, and reduced ability to respond to additional stressors.

• Höglund, Erik; Moltesen, Maria; Castanheira, Maria Filipa; Thörnqvist, Per-Ove; Silva, Patricia IM & Øverli, Øyvind [Show all 8 contributors for this article] (2020). Contrasting neurochemical and behavioral profiles reflects stress coping styles but not stress responsiveness in farmed gilthead seabream (Sparus aurata). Physiology and Behavior. ISSN 0031-9384. 214. doi: 10.1016/j.physbeh.2019.112759. Full text in Research Archive Show summary

  In fish, as well as in other vertebrates, contrasting suites of physiological and behavioral traits, or coping styles, are often shown in response to stressors. However, the magnitude of the response (i.e. stress responsiveness) has been suggested to be independent of stress coping style. One central neurotransmitter that has been associated with both stress responsiveness and differences in stress coping styles is serotonin (5-hydroxytryptamine, 5-HT). In this study, we investigated to what extent stress responsiveness reflects differences in stress coping, and the potential involvement of the 5-HT system in mediating such differences in farmed Gilthead seabream. Initially, fish were classified as proactive or reactive based on their behavioural response to net restraint. Following 1.5 months, fish classified as proactive still showed a higher number of escape attempts and spent longer time escaping than those classified as reactive. These differences were reflected in a generally higher brain stem 5-HT concentration and a lower telencephalic 5-HT activity, i.e. the ratio of 5-hydroxyindoleacetic acid (5-HIAA) to 5-HT, in proactive fish. Independent of stress coping styles, stress responsiveness was reflected in elevated 5-HIAA concentrations and 5-HIAA/5-HT ratios in telencephalon and brain stem together with increased plasma cortisol concentrations at 0.5 and 2 h following the last net restraint. The current results show that 5-HT signaling can reflect different behavioural output to a challenge which are independent of neuroendocrine responses to stress and lend support to the hypothesis that stress coping styles can be independent of stress responsiveness.

• Ferrari, Sebastien; Rey, Sonia; Höglund, Erik; Øverli, Øyvind; Chatain, Beatrice & MacKenzie, Simon [Show all 7 contributors for this article] (2020). Physiological responses during acute stress recovery depend on stress coping style in European sea bass, Dicentrarchus labrax. Physiology and Behavior. ISSN 0031-9384. 216. doi: 10.1016/j.physbeh.2020.112801. Full text in Research Archive Show summary

  Individual stress coping style (reactive, intermediate and proactive) was determined in 3 groups of 120 pit tagged European seabass using the hypoxia avoidance test. The same three groups (no change in social composition) were then reared according to the standards recommended for this species. Then, 127 days later, individuals initially characterized as reactive, intermediate or proactive were submitted to an acute confinement stress for 30 min. Blood samples were taken to measure plasma cortisol levels 30 min (Stress30) or 150 min (Stress150) after the end of the confinement stress. Individuals were then sacrificed to sample the telencephalon in order to measure the main monoamines and their catabolites (at Stress30 only). Individuals from Stress150 were sampled for whole brain for a transcriptomic analysis. The main results showed that reactive individuals had a lower body mass than intermediate individuals which did not differ from proactive individuals. The physiological cortisol response did not differ between coping style at Stress30 but at Stress150 when intermediate and proactive individuals had recovered pre stress levels, reactive individuals showed a significant higher level illustrating a modulation of stress recovery by coping style. Serotonin turnover ratio was higher in proactive and reactive individuals compared to intermediate individuals and a significant positive correlation was observed with cortisol levels whatever the coping style. Further, the confinement stress led to a general increase in the serotonin turnover comparable between coping styles. Stress150 had a significant effect on target mRNA copy number (Gapdh mRNA copy number decreased while ifrd1 mRNA copy number increased) and such changes tended to depend upon coping style.

• Höglund, Erik; Øverli, Øyvind & Åtland, Åse (2020). Assaying waterborne psychoactive drugs by the response to naturalistic predator cues in the stickleback (Gasterosteus aculeatus). Science of the Total Environment. ISSN 0048-9697. 737. doi: 10.1016/j.scitotenv.2020.140257. Full text in Research Archive Show summary

  Ecotoxicological effects of psychiatric drugs and drug metabolites released by the human population are of increasing environmental concern. In this study we evaluate behavioral responses to visual predator cues in wild caught three-spined stickleback (Gasterosteus aculeatus) after exposure to water-born citalopram, a widely prescribed selective serotonin reuptake inhibitor with antidepressant and anxiolytic effects. Fish were exposed to ecological relevant concentrations of citalopram (0.15 or 1.5 μg L−1) for 10 or 20 days. After drug exposure, individual fish were moved to a test arena where they were exposed to two naturalistic visual predator cues; a shadow from beneath, which simulated an approaching fish, and an overhead silhouette of a passing gull. Both visual cues resulted in decreased locomotor activity after post cue presentation. Notably, citalopram exposure resulted in a dose dependent suppression in response to the overhead stimulus. These results show that an ecologically relevant stimulus elicits a robust avoidance behavioral in wild caught fish after 25 min of acclimatization in the test arena. This suggests that the gull stimulus can be utilized as a behavioral endpoint in high flow through assays of ecotoxicological effects of psychiatric drugs and drug metabolites. Furthermore, the short acclimation time of wild caught fish in the test arena, opens for behavioral screening by fish living or kept in water bodies which are potentially impacted by psychiatric drugs.

• Haraldstad, Tormod; Höglund, Erik; Kroglund, Frode; Olsen, Esben Moland; Hawley, Kate Louise & Haugen, Thrond Oddvar (2020). Anthropogenic and natural size-related selection act in concert during brown trout (Salmo trutta) smolt river descent. Hydrobiologia. ISSN 0018-8158. 2020. doi: 10.1007/s10750-020-04329-4. Full text in Research Archive Show summary

  By hindering migration and inducing direct turbine mortality during downstream migration, hydropower is regarded as one of the most serious threats to anadromous salmonids. Yet, little attention has been paid to long-term turbine-induced selection mechanisms effecting fish populations. This work evaluates turbine and post-turbine survival of PIT-tagged wild brown trout smolts. By estimating individual river and sea survival rates, we were able to compare survival rates of smolts that had migrated through the turbine with smolts that had bypassed the turbine, as well as investigate both natural and anthropogenic size-selective mechanisms operative on the population. Total river-descent survival probability was 0.20 for turbine migrants and 0.44 for bypass migrants. The surviving turbine migrants were significantly smaller than their bypass counterparts and more exposed to predation from Northern pike. The estimated mean-adjusted selection gradient was − 0.76 for turbine migrants and + 1.85 for the bypass migrants. The resulting disruptive selection may ultimately lead to increased phenotypic smolt size variation provided sufficient additive genetic variance associated with smolt size. Mitigation measures at hydropower plants are thus essential for preserving sustainable populations of anadromous fish and maintaining population genetic variation.

• Höglund, Erik; Schröder, Ingrid Agneta; Möller, Margareta; Andersson-Hagiwara, Magnus & Ohlsson-Nevo, Emma (2019). The ambulance nurse experiences of non-conveying patients. Journal of Clinical Nursing (JCN). ISSN 0962-1067. 28(1-2), p. 235–244. doi: 10.1111/jocn.14626. Full text in Research Archive
• Höglund, Erik; Øverli, Øyvind & Winberg, Svante (2019). Tryptophan Metabolic Pathways and Brain Serotonergic Activity: A Comparative Review. Frontiers in Endocrinology. 10. doi: 10.3389/fendo.2019.00158. Full text in Research Archive Show summary

  The essential amino acid L-tryptophan (Trp) is the precursor of the monoaminergic neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). Numerous studies have shown that elevated dietary Trp has a suppressive effect on aggressive behavior and post-stress plasma cortisol concentrations in vertebrates, including teleosts. These effects are believed to be mediated by the brain serotonergic system, even though all mechanisms involved are not well understood. The rate of 5-HT biosynthesis is limited by Trp availability, but only in neurons of the hindbrain raphe area predominantly expressing the isoform TPH2 of the enzyme tryptophan hydroxylase (TPH). In the periphery as well as in brain areas expressing TPH1, 5-HT synthesis is probably not restricted by Trp availability. Moreover, there are factors affecting Trp influx to the brain. Among those are acute stress, which, in contrast to long-term stress, may result in an increase in brain Trp availability. The mechanisms behind this stress induced increase in brain Trp concentration are not fully understood but sympathetic activation is likely to play an important role. Studies in mammals show that only a minor fraction of Trp is utilized for 5-HT synthesis whereas a larger fraction of the Trp pool enters the kynurenic pathway. The first stage of this pathway is catalyzed by the hepatic enzyme tryptophan 2,3-dioxygenase (TDO) and the extrahepatic enzyme indoleamine 2,3-dioxygenase (IDO), enzymes that are induced by glucocorticoids and pro-inflammatory cytokines, respectively. Thus, chronic stress and infections can shunt available Trp toward the kynurenic pathway and thereby lower 5-HT synthesis. In accordance with this, dietary fatty acids affecting the pro-inflammatory cytokines has been suggested to affect metabolic fate of Trp. While TDO seems to be conserved by evolution in the vertebrate linage, earlier studies suggested that IDO was only present mammals. However, recent phylogenic studies show that IDO paralogues are present within the whole vertebrate linage, however, their involvement in the immune and stress reaction in teleost fishes remains to be investigated. In this review we summarize the results from previous studies on the effects of dietary Trp supplementation on behavior and neuroendocrinology, focusing on possible mechanisms involved in mediating these effects.

• Haraldstad, Tormod; Haugen, Thrond Oddvar; Kroglund, Frode; Olsen, Esben Moland & Höglund, Erik (2019). Migratory passage structures at hydropower plants as potential physiological and behavioural selective agents. Royal Society Open Science. 6(11). doi: 10.1098/rsos.190989. Full text in Research Archive Show summary

  Anthropogenic activities affect fish populations worldwide. River dams have profound impacts on ecosystems by changing habitats and hindering migration. In an effort to counteract such effects, a range of mitigation measures have been installed at hydroelectric power plants. However, not all individuals in a population use these measures, potentially creating strong selection processes at hydroelectric power plants. This may be especially true during migration; fish can get heavily delayed or pass through a hydropower turbine, thus facing increased mortality compared with those using a safe bypass route. In this study, we quantify migration route choices of descending wild passive integrated transponder (PIT)-tagged Atlantic salmon smolts released upstream from a hydroelectric plant. We demonstrate how only a few metres’ displacement of bypass canals can have a large impact on the fish guidance efficiency (FGE). The proportion of fish using the bypasses increased from 1% to 34% when water was released in surface gates closer to the turbine intake. During a period of low FGE, we observed two different smolt migratory strategies. While some individuals spent little time in the forebay before migrating through the turbine tunnel, others remained there. We suggest that these groups represent different behavioural types, and that suboptimal mitigation measures at hydropower intakes may, therefore, induce strong selection on salmon behavioural traits. The ultimate outcome of these selection mechanisms is discussed in light of potential trade-offs between turbine migration mortality coast and optimal sea entrance timing survival benefits.

• Damsgård, Børge; Evensen, Tor Hatten; Øverli, Øyvind; Gorissen, Marnix; Ebbesson, Lars O.E. & Rey, Sonia [Show all 7 contributors for this article] (2019). Proactive avoidance behaviour and pace-of-life syndrome in Atlantic salmon. Royal Society Open Science. 6(3). doi: 10.1098/rsos.181859. Full text in Research Archive Show summary

  Individuals in a fish population differ in key life-history traits such as growth rate and body size. This raises the question of whether such traits cluster along a fast-slow growth continuum according to a pace-of-life syndrome (POLS). Fish species like salmonids may develop a bimodal size distribution, providing an opportunity to study the relationships between individual growth and behavioural responsiveness. Here we test whether proactive characteristics (bold behaviour coupled with low post-stress cortisol production) are related to fast growth and developmental rate in Atlantic salmon, Salmo salar. Boldness was tested in a highly controlled two-tank hypoxia test were oxygen levels were gradually decreased in one of the tanks. All fish became inactive close to the bottom at 70% oxygen saturation. At 40% oxygen saturation level a fraction of the fish actively sought to avoid hypoxia. A proactive stress coping style was verified by lower cortisol response to a standardized stressor. Two distinct clusters of bimodal growth trajectories were identified, with fast growth and early smoltification in 80% of the total population. There was a higher frequency of proactive than reactive individuals in this fast-developing fraction of fish. The smolts were associated with higher post-stress plasma cortisol than parr, and the proactive smolts leaving hypoxia had significant lower post-stress cortisol than the stayers. The study demonstrated a link between a proactive coping and fast growth and developmental ratio and suggests that selection for domestic production traits promotes this trait cluster.

• Haraldstad, Tormod; Höglund, Erik; Kroglund, Frode; Lamberg, Anders; Olsen, Esben Moland & Haugen, Thrond Oddvar (2018). Condition-dependent skipped spawning in anadromous brown trout (Salmo trutta). Canadian Journal of Fisheries and Aquatic Sciences. ISSN 0706-652X. 75(12), p. 2313–2319. doi: 10.1139/cjfas-2017-0076. Full text in Research Archive Show summary

  Repeat spawners of anadromous salmonids may contribute significantly to population resilience by providing multiple cohorts to both seawater and freshwater life stages. In this study, winter survival of sea trout (Salmo trutta Linnaeus, 1758) post spawners (kelts) was 89%. Sea survival increased linearly with female length with a return probability between 30% and 50%, whereas males attained a maximum return probability of 60% at 520 mm. Of the returning sea trout, 40% skipped spawning and they had significantly lower condition factor as kelts compared with those who returned after one summer. These results suggest that sex-specific differences in individual post-spawning growth–survival trade-off exist and that energetic status of descending kelts may influence the probability to skip spawning. We discuss to what extent hydropower may reduce post-spawning survival due to blocking of river descent opportunities, potentially altering the fitness landscape and favouring new life-history adaptations. From a management perspective, it is concluded that it is crucial to maintain connectivity in regulated rivers, allowing fish to complete repetitive spawning and feeding migrations, thus contributing to population productivity.

• Samaras, Athanasios; Santo, Carlos Espirito; Papandroulakis, Nikos; Mitrizakis, Nikolaos; Pavlidis, Michail & Höglund, Erik [Show all 13 contributors for this article] (2018). Allostatic Load and Stress Physiology in European Seabass (Dicentrarchus labrax L.) and Gilthead Seabream (Sparus aurata L.). Frontiers in Endocrinology. 9. doi: 10.3389/fendo.2018.00451. Full text in Research Archive Show summary

  The present study aimed to compare effects of increasing chronic stress load on the stress response of European seabass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata) to identify neuroendocrine functions that regulate this response. Fish were left undisturbed (controls) or exposed to three levels of chronic stress for 3 weeks and then subjected to an acute stress test (ACT). Chronic stress impeded growth and decreased feed consumption in seabass, not in seabream. In seabass basal cortisol levels are high and increase with stress load; the response to a subsequent ACT decreases with increasing (earlier) load. Basal cortisol levels in seabream increase with the stress load, whereas the ACT induced a similar response in all groups. In seabass and seabream plasma α-MSH levels and brain stem serotonergic activity and turnover were similar and not affected by chronic stress. Species-specific molecular neuro-regional differences were seen. In-situ hybridization analysis of the early immediate gene cfos in the preoptic area showed ACT-activation in seabream; in seabass the expression level was not affected by ACT and seems constitutively high. In seabream, expression levels of telencephalic crf, crfbp, gr1, and mr were downregulated; the seabass hypothalamic preoptic area showed increased expression of crf and gr1, and decreased expression of mr, and this increased the gr1/mr ratio considerably. We substantiate species-specific physiological differences to stress coping between seabream and seabass at an endocrine and neuroendocrine molecular level. Seabass appear less resilient to stress, which we conclude from high basal activities of stress-related parameters and poor, or absent, responses to ACT. This comparative study reveals important aquaculture, husbandry, and welfare implications for the rearing of these species.

• Haraldstad, Tormod; Höglund, Erik; Kroglund, Frode; Haugen, Thrond Oddvar & Forseth, Torbjørn (2018). Common mechanisms for guidance efficiency of descending Atlantic salmon smolts in small and large hydroelectric power plants. River Research and Applications. ISSN 1535-1459. 34(9), p. 1179–1185. doi: 10.1002/rra.3360. Full text in Research Archive Show summary

  Dams and turbines associated with hydroelectric power plants (HEP) disrupt connec- tivity by affecting fish movement and survival. There has been an increasing focus on measures to facilitate downstream migration at HEPs. The fish guidance efficacy (FGE) of downstream mitigation measures largely remains suboptimal and calls for development of knowledge on factors influencing FGE. In this study, we analyse 6 years of wild Atlantic salmon smolt passive integrated transponder (PIT)‐telemetry data (N = 1,498) from a neighbouring small‐ and a large‐scale HEP. Timing of the smolt migration period was significantly different between the two rivers. Thus, river‐ specific smolt‐run timing is imperative for proper measures management in regulated rivers aiming at maximizing smolt‐descent survival. A generalized linear model including additive effects of relative bypass discharge and scaled river discharge on the FGE for descending smolts received highest Akaike's information criterion support in the data and explained 74.2% of the FGE variation. This model, including no river effect, predicted high FGE (up to 90%) at low river flow (≤30% of HEP maximum capacity) when 7% of the water is allocated through the bypass. Many run‐of‐the‐river HEPs have highly variable river flow during the smolt‐run period. Our model suggests that these HEPs could utilize their manoeuvre flexibility to obtain water allocation routines between bypass and turbines that optimize both FGE and hydroelectric production. bypass, fish guidance efficiency, passive integrated transponders, run‐of‐the‐river, salmonids

• Vindas, Marco A; Fokos, Stefanos; Pavlidis, Michail; Höglund, Erik; Dionysopoulou, Sylvia & Ebbesson, Lars OE [Show all 8 contributors for this article] (2018). Early life stress induces long-term changes in limbic areas of a teleost fish: The role of catecholamine systems in stress coping. Scientific Reports. 8. doi: 10.1038/s41598-018-23950-x. Full text in Research Archive Show summary

  Early life stress (ELS) shapes the way individuals cope with future situations. Animals use cognitive flexibility to cope with their ever-changing environment and this is mainly processed in forebrain areas. We investigated the performance of juvenile gilthead seabream, previously subjected to an ELS regime. ELS fish showed overall higher brain catecholaminergic (CA) signalling and lower brain derived neurotrophic factor (bdnf) and higher cfos expression in region-specific areas. All fish showed a normal cortisol and serotonergic response to acute stress. Brain dopaminergic activity and the expression of the α2Α adrenergic receptor were overall higher in the fish homologue to the lateral septum (Vv), suggesting that the Vv is important in CA system regulation. Interestingly, ELS prevented post-acute stress downregulation of the α2Α receptor in the amygdala homologue (Dm3). There was a lack of post-stress response in the β2 adrenergic receptor expression and a downregulation in bdnf in the Dm3 of ELS fish, which together indicate an allostatic overload in their stress coping ability. ELS fish showed higher neuronal activity (cfos) post-acute stress in the hippocampus homologue (Dlv) and the Dm3. Our results show clear long-term effects on limbic systems of seabream that may compromise their future coping ability to environmental challenges.

• Höglund, Erik; Øverli, Øyvind; Andersson, Madelene Åberg; Silva, Patricia; Laursen, Danielle Caroline & Moltesen, Maria M [Show all 12 contributors for this article] (2017). Dietary l-tryptophan leaves a lasting impression on the brain and the stress response. British Journal of Nutrition. ISSN 0007-1145. 117(10), p. 1351–1357. doi: 10.1017/S0007114517001428. Full text in Research Archive Show summary

  Comparative models suggest that effects of dietary tryptophan (Trp) on brain serotonin (5-hydroxytryptamine; 5-HT) neurochemistry and stress responsiveness are present throughout the vertebrate lineage. Moreover, hypothalamic 5-HT seems to play a central role in control of the neuroendocrine stress axis in all vertebrates. Still, recent fish studies suggest long-term effects of dietary Trp on stress responsiveness, which are independent of hypothalamic 5-HT. Here, we investigated if dietary Trp treatment may result in long-lasting effects on stress responsiveness, including changes in plasma cortisol levels and 5-HT neurochemistry in the telencephalon and hypothalamus of Atlantic salmon. Fish were fed diets containing one, two or three times the Trp content in normal feed for 1 week. Subsequently, fish were reintroduced to control feed and were exposed to acute crowding stress for 1 h, 8 and 21 d post Trp treatment. Generally, acute crowding resulted in lower plasma cortisol levels in fish treated with 3 × Trp compared with 1 × Trp- and 2 × Trp-treated fish. The same general pattern was reflected in telencephalic 5-HTergic turnover, for which 3 × Trp-treated fish showed decreased values compared with 2 × Trp-treated fish. These long-term effects on post-stress plasma cortisol levels and concomitant 5-HT turnover in the telencephalon lends further support to the fact that the extrahypothalamic control of the neuroendocrine stress response is conserved within the vertebrate lineage. Moreover, they indicate that trophic/structural effects in the brain underlie the effects of dietary Trp treatment on stress reactivity.

• Höglund, Erik; Silva, Patricia IM; Vindas, Marco Antonio & Øverli, Øyvind (2017). Contrasting Coping Styles Meet the Wall: A Dopamine Driven Dichotomy in Behavior and Cognition. Frontiers in Neuroscience. ISSN 1662-4548. 11. doi: 10.3389/fnins.2017.00383. Full text in Research Archive Show summary

  Individual variation in the ability to modify previously learned behavior is an important dimension of trait correlations referred to as coping styles, behavioral syndromes or personality. These trait clusters have been shaped by natural selection, and underlying control mechanisms are often conserved throughout vertebrate evolution. In teleost fishes, behavioral flexibility and coping style have been studied in the high (HR) and low-responsive (LR) rainbow trout lines. Generally, proactive LR trout show a behavior guided by previously learned routines, while HR trout show a more flexible behavior relying on environmental cues. In mammals, routine dependent vs. flexible behavior has been connected to variation in limbic dopamine (DA) signaling. Here, we studied the link between limbic DA signaling and individual variation in flexibility in teleost fishes by a reversal learning approach. HR/LR trout were challenged by blocking a learned escape route, previously available during interaction with a large and aggressive conspecific. LR trout performed a higher number of failed escape attempts against the transparent blockage, while HR trout were more able to inhibit the now futile escape impulse. Regionally discrete changes in DA neurochemistry were observed in micro dissected limbic areas of the telencephalon. Most notably, DA utilization in the dorsomedial telencephalon (DM, a suggested amygdala equivalent) remained stable in HR trout in response to reversal learning under acute stress, while increasing from an initially lower level in LR trout. In summary, these results support the view that limbic homologs control individual differences in behavioral flexibility even in non-mammalian vertebrates.

• Castanheira, Maria Filipa; Conceição, Luis E.C.; Millot, Sandie; Rey, Sonia; Bégout, Marie-Laure & Damsgård, Børge [Show all 10 contributors for this article] (2017). Coping styles in farmed fish: consequences for aquaculture. Reviews in Aquaculture. ISSN 1753-5123. 9(1), p. 23–41. doi: 10.1111/raq.12100. Full text in Research Archive Show summary

  Individual differences in physiological and behavioural responses to stressors are increasingly recognised as adaptive variation and thus raw material for evolution and fish farming improvements including selective breeding. Such individual variation has been evolutionarily conserved and is present in all vertebrate taxa including fish. In farmed animals, the interest in consistent trait associations, that is coping styles, has increased dramatically over the last years because many studies have demonstrated links to performance traits, health and disease susceptibility and welfare. This study will review (i) the main behavioural, neuroendocrine, cognitive and emotional differences between reactive and proactive coping styles in farmed fish; (ii) the methodological approaches used to identify coping styles in farmed fish, including individual (group) mass‐screening tests; and (iii) how knowledge on coping styles may contribute to improved sustainability of the aquaculture industry, including welfare and performance of farmed fish. Moreover, we will suggest areas for future research, where genetic basis (heritability/epigenetic) of coping styles, and the neuroendocrine mechanisms behind consistent as well as flexible behavioural patterns are pinpointed as central themes. In addition, the ontogeny of coping styles and the influence of age, social context and environmental change in coping styles will also be discussed.

• Vindas, Marco Antonio; Gorissen, Marnix; Höglund, Erik; Flik, Gert; Tronci, Valentina & Damsgård, Børge [Show all 11 contributors for this article] (2017). How do individuals cope with stress? Behavioural, physiological and neuronal differences between proactive and reactive coping styles in fish. Journal of Experimental Biology. ISSN 0022-0949. 220(8), p. 1524–1532. doi: 10.1242/jeb.153213. Full text in Research Archive
• Johansen, Ida Beitnes; Sandblom, Erik; Skov, Peter V.; Gräns, Albin; Ekström, Andreas & Lunde, Ida Gjervold [Show all 13 contributors for this article] (2017). Bigger is not better: cortisol-induced cardiac growth and dysfunction in salmonids. Journal of Experimental Biology. ISSN 0022-0949. 220(14), p. 2545–2553. doi: 10.1242/jeb.135046. Full text in Research Archive Show summary

  Stress and elevated cortisol levels are associated with pathological heart growth and cardiovascular disease in humans and other mammals. We recently established a link between heritable variation in post-stress cortisol production and cardiac growth also in salmonid fish. A conserved stimulatory effect of the otherwise catabolic steroid hormone cortisol is likely implied, but has to date not been established experimentally. Furthermore, whereas cardiac growth is associated with failure of the mammalian heart, pathological cardiac hypertrophy has not previously been described in fish. Here we show that rainbow trout (Oncorhynchus mykiss) treated with cortisol in the food for 45 days have enlarged hearts with lower maximum stroke volume and cardiac output. In accordance with impaired cardiac performance, overall circulatory oxygen transporting capacity was diminished as indicated by reduced aerobic swimming performance. In contrast to the well-known adaptive/physiological heart growth observed in fish, cortisol-induced growth is maladaptive. Furthermore, the observed heart growth was associated with up-regulated signature genes of mammalian cardiac pathology, suggesting that signaling pathways mediating cortisol-induced cardiac remodeling in fish are conserved from fish to mammals. Altogether, we show that excessive cortisol can induce pathological cardiac remodeling. This is the first study to report and integrate the etiology, physiology and molecular biology of cortisol-induced pathological remodeling in fish.

• Vindas, Marco Antonio; Madaro, Angelico; Fraser, Thomas; Höglund, Erik; Olsen, Rolf Erik & Kristiansen, Tore S [Show all 7 contributors for this article] (2017). Uncontrollable chronic stress reduces growth disparities in farmed Atlantic salmon. Physiology and Behavior. ISSN 0031-9384. 179, p. 246–252. doi: 10.1016/j.physbeh.2017.06.012. Full text in Research Archive
• Moltesen, Maria; Laursen, Danielle Caroline; Thörnquist, Per-Ove; Andersson, Madelene Åberg; Winberg, Svante & Höglund, Erik (2016). Effects of acute and chronic stress on telencephalic neurochemistry and gene expression in rainbow trout (Oncorhynchus mykiss). Journal of Experimental Biology. ISSN 0022-0949. 219(24), p. 3907–3914. doi: 10.1242/jeb.139857. Full text in Research Archive Show summary

  By filtering relevant sensory inputs and initiating stress responses, the brain is an essential organ in stress coping and adaptation. However, exposure to chronic or repeated stress can lead to allostatic overload, where neuroendocrinal and behavioral reactions to stress become maladaptive. This work examines forebrain mechanisms involved in allostatic processes in teleost fishes. Plasma cortisol, forebrain serotonergic (5-HTergic) neurochemistry, and mRNA levels of corticotropin-releasing factor (CRF), CRF-binding protein (CRF-BP), CRF receptors (CRFR1 and CRFR2), mineralocorticoid receptor (MR), glucocorticoid receptors (GR1 and GR2) and serotonin type 1A (5-HT1A) receptors (5-HT1Aα and 5-HT1Aβ) were investigated at 1 h before and 0, 1 and 4 h after acute stress, in two groups of rainbow trout held in densities of 25 and 140 kg m−3 for 28 days. Generally, being held at 140 kg m−3 resulted in a less pronounced cortisol response. This effect was also reflected in lower forebrain 5-HTergic turnover, but not in mRNA levels in any of the investigated genes. This lends further support to reports that allostatic load causes fish to be incapable of mounting a proper cortisol response to an acute stressor, and suggests that changes in forebrain 5-HT metabolism are involved in allostatic processes in fish. Independent of rearing densities, mRNA levels of 5-HT1Aα and MR were downregulated 4 h post-stress compared with values 1 h post-stress, suggesting that these receptors are under feedback control and take part in the downregulation of the hypothalamic–pituitary–interrenal (HPI) axis after exposure to an acute stressor.

• Vindas, Marco Antonio; Johansen, Ida Beitnes; Folkedal, Ole; Höglund, Erik; Gorissen, Marnix & Flik, Gert [Show all 8 contributors for this article] (2016). Brain serotonergic activation in growth-stunted farmed salmon: Adaption versus pathology. Royal Society Open Science. 3(5). doi: 10.1098/rsos.160030. Full text in Research Archive Show summary

  Signalling systems activated under stress are highly conserved, suggesting adaptive effects of their function. Pathologies arising from continued activation of such systems may represent a mismatch between evolutionary programming and current environments. Here, we use Atlantic salmon (Salmo salar) in aquaculture as a model to explore this stance of evolutionary-based medicine, for which empirical evidence has been lacking. Growth-stunted (GS) farmed fish were characterized by elevated brain serotonergic activation, increased cortisol production and behavioural inhibition. We make the novel observation that the serotonergic system in GS fish is unresponsive to additional stressors, yet a cortisol response is maintained. The inability of the serotonergic system to respond to additional stress, while a cortisol response is present, probably leads to both imbalance in energy metabolism and attenuated neural plasticity. Hence, we propose that serotonin-mediated behavioural inhibition may have evolved in vertebrates to minimize stress exposure in vulnerable individuals.

• Moltesen, Maria; Vindas, Marco Antonio; Winberg, Svante; Ebbesson, Lars; Ruiz-Gomez, Maria de Lourdes & Skov, Peter Vilhelm [Show all 9 contributors for this article] (2016). Cognitive appraisal of aversive stimulus differs between individuals with contrasting stress coping styles; evidences from selected rainbow trout (Oncorhynchus mykiss) strains. Behaviour. ISSN 0005-7959. 153(13-14), p. 1567–1587. doi: 10.1163/1568539X-00003405. Full text in Research Archive
• Vindas, Marco A.; Madaro, Angelico; Fraser, Thomas W.K.; Höglund, Erik; Olsen, Rolf E. & Øverli, Øyvind [Show all 7 contributors for this article] (2016). Coping with a changing environment: the effects of early life stress. Royal Society Open Science. 3:160382(10). doi: 10.1098/rsos.160382. Full text in Research Archive Show summary

  Ongoing rapid domestication of Atlantic salmon implies that individuals are subjected to evolutionarily novel stressors encountered under conditions of artificial rearing, requiring new levels and directions of flexibility in physiological and behavioural coping mechanisms. Phenotypic plasticity to environmental changes is particularly evident at early life stages. We investigated the performance of salmon, previously subjected to an unpredictable chronic stress (UCS) treatment at an early age (10 month old parr), over several months and life stages. The UCS fish showed overall higher specific growth rates compared with unstressed controls after smoltification, a particularly challenging life stage, and after seawater transfer. Furthermore, subjecting fish to acute stress at the end of the experiment, we found that UCS groups had an overall lower hypothalamic catecholaminergic and brain stem serotonergic response to stress compared with control groups. In addition, serotonergic activity was negatively correlated with final growth rates, which implies that serotonin responsive individuals have growth disadvantages. Altogether, our results may imply that a subdued monoaminergic response in stressful farming environments may be beneficial, because in such situations individuals may be able to reallocate energy from stress responses into other life processes, such as growth.

• Winberg, Svante; Höglund, Erik & Øverli, Øyvind (2016). Variation in the Neuroendocrine Stress Response. In Schreck, Carl B.; Tort, Lluis; Farrell, Anthony P. & Brauner, Colin J. (Ed.), Biology of Stress in Fish. Academic Press. ISSN 9780128027370. p. 35–74. doi: 10.1016/B978-0-12-802728-8.00002-3. Full text in Research Archive
• Kahn, Uniza Wahid; Øverli, Øyvind; Hinkle, Patricia M.; Pasha, Farhan Ahmad; Johansen, Ida Beitnes & Berget, Ingunn [Show all 11 contributors for this article] (2016). A novel role for pigment genes in the stress response in rainbow trout (Oncorhynchus mykiss). Scientific Reports. 6. doi: 10.1038/srep28969. Full text in Research Archive Show summary

  In many vertebrate species visible melanin-based pigmentation patterns correlate with high stress- and disease-resistance, but proximate mechanisms for this trait association remain enigmatic. Here we show that a missense mutation in a classical pigmentation gene, melanocyte stimulating hormone receptor (MC1R), is strongly associated with distinct differences in steroidogenic melanocortin 2 receptor (MC2R) mRNA expression between high- (HR) and low-responsive (LR) rainbow trout (Oncorhynchus mykiss). We also show experimentally that cortisol implants increase the expression of agouti signaling protein (ASIP) mRNA in skin, likely explaining the association between HR-traits and reduced skin melanin patterning. Molecular dynamics simulations predict that melanocortin 2 receptor accessory protein (MRAP), needed for MC2R function, binds differently to the two MC1R variants. Considering that mRNA for MC2R and the MC1R variants are present in head kidney cells, we hypothesized that MC2R activity is modulated in part by different binding affinities of the MC1R variants for MRAP. Experiments in mammalian cells confirmed that trout MRAP interacts with the two trout MC1R variants and MC2R, but failed to detect regulation of MC2R signaling, possibly due to high constitutive MC1R activity.

• Larsen, Martin H.; Johnsson, Jörgen I.; Winberg, Svante; Wilson, Alexander D.M.; Hammenstig, David & Thörnqvist, Per-Ove [Show all 9 contributors for this article] (2015). Effects of emergence time and early social rearing environment on behaviour of Atlantic salmon: Consequences for juvenile fitness and smolt migration. PLOS ONE. 10(3). doi: 10.1371/journal.pone.0119127. Full text in Research Archive Show summary

  Consistent individual differences in behaviour have been well documented in a variety of animal taxa, but surprisingly little is known about the fitness and life-history consequences of such individual variation. In wild salmonids, the timing of fry emergence from gravel spawning nests has been suggested to be coupled with individual behavioural traits. Here, we further investigate the link between timing of spawning nest emergence and behaviour of Atlantic salmon (Salmo salar), test effects of social rearing environment on behavioural traits in fish with different emergence times, and assess whether behavioural traits measured in the laboratory predict growth, survival, and migration status in the wild. Atlantic salmon fry were sorted with respect to emergence time from artificial spawning nest into three groups: early, intermediate, and late. These emergence groups were hatchery-reared separately or in co-culture for four months to test effects of social rearing environment on behavioural traits. Twenty fish from each of the six treatment groups were then subjected to three individual-based behavioural tests: basal locomotor activity, boldness, and escape response. Following behavioural characterization, the fish were released into a near-natural experimental stream. Results showed differences in escape behaviour between emergence groups in a net restraining test, but the social rearing environment did not affect individual behavioural expression. Emergence time and social environment had no significant effects on survival, growth, and migration status in the stream, although migration propensity was 1.4 to 1.9 times higher for early emerging individuals that were reared separately. In addition, despite individuals showing considerable variation in behaviour across treatment groups, this was not translated into differences in growth, survival, and migration status. Hence, our study adds to the view that fitness (i.e., growth and survival) and life-history predictions from laboratory measures of behaviour should be made with caution and ideally tested in nature.

• Thörnqvist, Per-Ove; Höglund, Erik & Winberg, Svante (2015). Natural selection constrains personality and brain gene expression Differences in Atlantic salmon (Salmo salar). Journal of Experimental Biology. ISSN 0022-0949. 218, p. 1077–1083. doi: 10.1242/jeb.114314. Full text in Research Archive
• Laursen, Danielle Caroline; Larsen, Bodil Katrine; Skov, Peter Vilhelm & Höglund, Erik (2015). Improved growth performance in rainbow trout Oncorhynchus mykiss reared at high densities is linked to increased energy retention. Aquaculture. ISSN 0044-8486. 442, p. 69–73. doi: 10.1016/j.aquaculture.2015.02.035. Full text in Research Archive
• Silva, Patricia; Martins, Catarina I.M.; Kahn, Uniza Wahid; Gjøen, Hans Magnus; Øverli, Øyvind & Höglund, Erik (2015). Stress and fear responses in the teleost pallium. Physiology and Behavior. ISSN 0031-9384. 141, p. 17–22. doi: 10.1016/j.physbeh.2014.12.020. Full text in Research Archive
• Silva, Patricia; Martins, Catarina I.M.; Höglund, Erik; Gjøen, Hans Magnus & Øverli, Øyvind (2014). Feeding motivation as a personality trait in Nile tilapia (Oreochromis niloticus): role of serotonergic neurotransmission. Fish Physiology & Biochemistry. ISSN 0920-1742. 40(5), p. 1547–1557. doi: 10.1007/s10695-014-9947-2. Full text in Research Archive
• Lund, Ivar; Höglund, Erik; Ebbesson, Lars O.E. & Skov, Peter Vilhelm (2014). Dietary LC-PUFA deficiency early in ontogeny induces behavioural changes in pike perch (Sander lucioperca) larvae and fry. Aquaculture. ISSN 0044-8486. 432, p. 453–461. doi: 10.1016/j.aquaculture.2014.05.039. Full text in Research Archive
• Vindas, Marco Antonio; Sørensen, Christina; Johansen, Ida Beitnes; Folkedal, Ole; Höglund, Erik & Kahn, Uniza Wahid [Show all 10 contributors for this article] (2014). Coping with unpredictability: Dopaminergic and neurotrophic responses to omission of expected reward in Atlantic salmon (Salmo salar L.). PLOS ONE. 9(1). doi: 10.1371/journal.pone.0085543. Full text in Research Archive Show summary

  Comparative studies are imperative for understanding the evolution of adaptive neurobiological processes such as neural plasticity, cognition, and emotion. Previously we have reported that prolonged omission of expected rewards (OER, or ‘frustrative nonreward’) causes increased aggression in Atlantic salmon (Salmo salar). Here we report changes in brain monoaminergic activity and relative abundance of brain derived neurotrophic factor (BDNF) and dopamine receptor mRNA transcripts in the same paradigm. Groups of fish were initially conditioned to associate a flashing light with feeding. Subsequently, the expected food reward was delayed for 30 minutes during two out of three meals per day in the OER treatment, while the previously established routine was maintained in control groups. After 8 days there was no effect of OER on baseline brain stem serotonin (5-HT) or dopamine (DA) activity. Subsequent exposure to acute confinement stress led to increased plasma cortisol and elevated turnover of brain stem DA and 5-HT in all animals. The DA response was potentiated and DA receptor 1 (D1) mRNA abundance was reduced in the OER-exposed fish, indicating a sensitization of the DA system. In addition OER suppressed abundance of BDNF in the telencephalon of non-stressed fish. Regardless of OER treatment, a strong positive correlation between BDNF and D1 mRNA abundance was seen in non-stressed fish. This correlation was disrupted by acute stress, and replaced by a negative correlation between BDNF abundance and plasma cortisol concentration. These observations indicate a conserved link between DA, neurotrophin regulation, and corticosteroid-signaling pathways. The results also emphasize how fish models can be important tools in the study of neural plasticity and responsiveness to environmental unpredictability.

• Vindas, Marco Antonio; Johansen, Ida Beitnes; Avitúa, Sergio Vela; Nørstrud, Karoline Sletbak; Aalgaard, Marion & Braastad, Bjarne [Show all 8 contributors for this article] (2014). Frustrative reward omission increases aggressive behaviour of inferior fighters. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 281(1784). doi: 10.1098/rspb.2014.0300. Full text in Research Archive
• Martins, Catarina I.M.; Silva, Patricia; Costas, Benjamin; Larsen, Bodil K.; Santos, Goncalo & Conceição, Luís E.C. [Show all 10 contributors for this article] (2013). The effect of tryptophan supplemented diets on brain serotonergic activity and plasma cortisol under undisturbed and stressed conditions in grouped-housed Nile tilapia Oreochromis niloticus. Aquaculture. ISSN 0044-8486. 400-401, p. 129–134. doi: 10.1016/j.aquaculture.2013.02.035. Full text in Research Archive
• Andersson, Madelene Åberg; Laursen, Danielle Caroline; Silva, Patricia & Höglund, Erik (2013). The relationship between emergence from spawning gravel and growth in farmed rainbow trout Oncorhynchus mykiss. Journal of Fish Biology. ISSN 0022-1112. 83(1), p. 214–219. doi: 10.1111/jfb.12153. Full text in Research Archive
• Åberg-Andersson, Madelene; Khan, Uniza Wahid; Øverli, Øyvind; Gjøen, Hans Magnus & Höglund, Erik (2013). Coupling between stress coping style and time of emergence from spawning nests in salmonid fishes: Evidence from selected rainbow trout strains (Oncorhynchus mykiss). Physiology and Behavior. ISSN 0031-9384. 116-117, p. 30–34. doi: 10.1016/j.physbeh.2013.03.019. Full text in Research Archive
• Laursen, Danielle Caroline; Andersson, Madelene Åberg; Silva, Patricia Isabel Mota; Petersson, Erik & Höglund, Erik (2013). Utilising spatial distribution in two-tank systems to investigate the level of aversiveness to crowding in farmed rainbow trout Oncorhynchus mykiss. Applied Animal Behaviour Science. ISSN 0168-1591. 144(3-4), p. 163–170. doi: 10.1016/j.applanim.2013.01.010. Full text in Research Archive
• Laursen, Danielle Caroline; Silva, Patricia; Larsen, Bodil Katrine & Höglund, Erik (2013). High oxygen consumption rates and scale loss indicate elevated aggressive behavior at low rearing density, while elevated serotonergic activity suggests chronic stress at high rearing densities in farmed rainbow trout. Physiology and Behavior. ISSN 0031-9384. 122, p. 147–154. doi: 10.1016/j.physbeh.2013.08.026. Full text in Research Archive
• Basic, Dean; Schjolden, Joachim; Krogdahl, Åshild; Krogh, Kristine von; Hillestad, Marie & Winberg, Svante [Show all 9 contributors for this article] (2013). Changes in regional brain monoaminergic activity and temporary down-regulation in stress response from dietary supplementation with L-tryptophan in Atlantic cod (Gadus morhua). British Journal of Nutrition. ISSN 0007-1145. 109, p. 2166–2174. doi: 10.1017/S0007114512004345. Full text in Research Archive
• Basic, Dean; Krogdahl, Åshild; Schjolden, Joachim; Winberg, Svante; Vindas, Marco A. & Hillestad, Marie [Show all 9 contributors for this article] (2013). Short- and long-term effects of dietary L-tryptophan supplementation on the neuroendocrine stress response in seawater-reared Atlantic salmon (Salmo salar). Aquaculture. ISSN 0044-8486. 388, p. 8–13. doi: 10.1016/j.aquaculture.2013.01.014. Full text in Research Archive
• Basic, Dean; Schjolden, Joachim; Krogdahl, Åshild; Krogh, Kristine von; Hillestad, Marie & Winberg, Svante [Show all 9 contributors for this article] (2012). Nutritional EndocrinologyChanges in regional brain monoaminergic activity and temporary down-regulation in stress response. British Journal of Nutrition. ISSN 0007-1145. doi: 10.1017/S0007114512004345. Full text in Research Archive
• Johansen, Ida Beitnes; Sørensen, Christina; Sandvik, Guro Katrine; Nilsson, Göran Erik; Höglund, Erik & Bakken, Morten [Show all 7 contributors for this article] (2012). Neural plasticity is affected by stress and heritable variation in stress coping style. Comparative Biochemistry and Physiology - Part D:Genomics and Proteomics. ISSN 1744-117X. 7(2), p. 161–171. doi: 10.1016/j.cbd.2012.01.002. Full text in Research Archive
• Madelene, Åberg Andersson & Höglund, Erik (2012). Linking personality to larval energy reserves in rainbow trout (Oncorhynchus mykiss). PLOS ONE. 7. doi: 10.1371/journal.pone.0049247. Full text in Research Archive
• Sacha, LeBlanc; Höglund, Erik; Kathleen, Gilmour & Suzanne, Currie (2012). Hormonal modulation of the heat shock response: insights from fish with divergent cortisol stress responses. American Journal of Physiology. Regulatory Integrative and Comparative Physiology. ISSN 0363-6119. 01. Full text in Research Archive
• Basic, Dean; Winberg, Svante; Schjolden, Joachim; Krogdahl, Åshild & Höglund, E. (2012). Context-dependent responses to novelty in Rainbow trout (Oncorhynchus mykiss), selected for high and low post-stress cortisol responsiveness. Physiology and Behavior. ISSN 0031-9384. 105(5), p. 1175–1181. doi: 10.1016/j.physbeh.2011.12.021. Full text in Research Archive
• Vaz, Jonathan Serrano; Ruiz-Gomez, Maria de Lourdes; Gjøen, Hans Magnus; Skov, Poul; Huntingford, F. A. & Øverli, Øyvind [Show all 7 contributors for this article] (2011). Consistent boldness behaviour in early emerging fry of domesticated Atlantic salmon (Salmo salar): Decoupling of behavioural and physiological traits of the proactive stress coping style. Physiology and Behavior. ISSN 0031-9384. 103(3-4), p. 359–364. doi: 10.1016/j.physbeh.2011.02.025. Full text in Research Archive
• Gomez, Maria de Lourdes Ruiz; Huntingford, Felicity; Øverli, Øyvind; Thörnqvist, Per-Ove & Höglund, Erik (2011). Response to environmental change in rainbow trout selected for divergent stress coping styles. Physiology and Behavior. ISSN 0031-9384. 102(3-4), p. 317–322. doi: 10.1016/j.physbeh.2010.11.023. Full text in Research Archive
• Andersson, M. Åberg; Silva, Patricia; Steffensen, JF & Höglund, E. (2011). Effects of maternal stress coping style on offspring characteristics in rainbow trout (Oncorhynchus mykiss). Hormones and Behavior. ISSN 0018-506X. 60(5), p. 699–705. doi: 10.1016/j.yhbeh.2011.09.008. Full text in Research Archive
• Laursen, Danielle Caroline; Olsen, Hanna; Ruiz-Gomez, Maria de Lourdes; Winberg, Svante & Höglund, Erik (2011). Behavioural responses to hypoxia provide a non-invasive method for distinguishing between stress coping styles in fish. Applied Animal Behaviour Science. ISSN 0168-1591. 132, p. 211–216. doi: 10.1016/j.applanim.2011.03.011. Full text in Research Archive
• Steenfeltd, Svend J; Lund, Ivar & Höglund, Erik (2011). Is batch variability in hatching time related to size heterogeneity and cannibalism in pikeperch (Sander lucioperca)? Aquaculture Research. ISSN 1355-557X. 132, p. 211–216. doi: 10.1016/j.applanim.2011.03.011. Full text in Research Archive
• Martins, Catarina I.M.; Silva, Patricia; Conceicao, Luis E.C.; Costas, Benjamin; Höglund, Erik & Øverli, Øyvind [Show all 7 contributors for this article] (2011). Linking Fearfulness and Coping Styles in Fish. PLOS ONE. 6(11). doi: 10.1371/journal.pone.0028084. Full text in Research Archive
• Lastein, Stine; Höglund, Erik; Overli, O; Øverli, Øyvind & Døving, Kjell Bjarne (2008). Effects of antalarmin, a CRF receptor 1 antagonist, on fright reaction and endocrine stress response in crucian carp (Carassius carassius). Journal of Comparative Physiology A. Sensory, neural, and behavioral physiology. ISSN 0340-7594. 194(12), p. 1007–1012. doi: 10.1007/s00359-008-0372-9. Full text in Research Archive Show summary

  The corticotrophin-releasing factor (CRF) receptors show striking homogeneity throughout the vertebrate subphylum. In mammals, the CRF1 receptor (CRFR1) plays an important role in mediating behavioral and endocrine responses to fear and stress. The specific roles of this receptor subtype in fear and stress reactions in non-mammalian vertebrates are largely unknown. Crucian carp displays the olfactory-mediated fright reaction, a stereotypic behavioral response to waterborne cues from damaged skin of conspecifics. This reaction shows several similarities to basic components of avoidance behavior in mammals. In the present study, we applied the non-peptide CRFR1 antagonist, antalarmin, to crucian carp 1 h before exposure to conspecific skin extract. This treatment resulted in a suppression of the fright reaction. After skin extract exposure, antalarmin treatment also lead to lower plasma cortisol values, as compared to vehicle treatment. This suppression of the behavioral fright reaction and the stress induced rise in plasma cortisol in crucian carp suggests that the functions of the CRFR1 are conserved by evolution.

• Höglund, Erik; Gjøen, Hans Magnus; Pottinger, Tom G. & Øverli, Øyvind (2008). Parental stress-coping styles affect the behaviour of rainbow trout Oncorhynchus mykiss at early developmental stages. Journal of Fish Biology. ISSN 0022-1112. 73(7), p. 1764–1769. doi: 10.1111/j.1095-8649.2008.02068.x. Full text in Research Archive Show summary

  This work examined behavioural responses in yolk-sac rainbow trout Oncorhynchus mykiss larvae originating from strains selected for high (HR) or low (LR) plasma cortisol response to a standardized stressor. The results showed that yolk-sac larvae originating from the HR strain were more sensitive to environmental stressors, in that they showed a shorter reaction time to low oxygen levels. Previous studies on adult and juvenile individuals from these strains demonstrated a number of correlated physiological and behavioural differences. In yolk-sac larvae, growth and development depended mainly on internal factors, which suggest that at least some aspects of stress-coping styles are inherent to the individual, before factors such as social experience or variable access to food resources could modify behavioural strategy.

• Lastein, Stine; Höglund, Erik; Mayer, Ian; Øverli, Øyvind & Døving, Kjell B. (2008). Female Crucian Carp, Carassius carassius, Lose Predator Avoidance Behavior when Getting Ready to Mate. Journal of Chemical Ecology. ISSN 0098-0331. 34(11), p. 1487–1491. Full text in Research Archive Show summary

  In predator-prey interactions, the prey often have to compromise fitness-related behaviors such as feeding, courting, and territorial defense in order to avoid predators. In these trade-off situations, some behaviors have priority over others. These priorities are not rigid, and may be context-dependent; for instance, many animals show increased risk-taking during courtship behavior by paying less attention to potential predators. We investigated whether the fright reaction, a stereotypical avoidance response to olfactory cues from injured conspecifics, may be affected by reproductive status in a teleost fish, the crucian carp. We demonstrate that among individuals not responding to alarm substances with a fright reaction, the majority were ovulated or spermiated. In females, mean plasma concentrations of 17 beta-estradiol and testosterone, gonadal steroids known to decrease during the later stages of sexual maturation, were lower in the individuals not responding with a fright reaction compared to those responding. In males, there were no differences between responsive and non-responsive individuals in mean plasma levels of androgens (testosterone and 11-ketotestosterone) involved in spermatogenesis and male sexual behavior. As the fright reaction in crucian carp consists of behavior incompatible with spawning behavior, we hypothesize that this short-term suppression of the alarm response has evolved so that spawning can occur uninterrupted.

• Ruiz-Gomez, MD; Kittilsen, S; Hoglund, E; Huntingford, FA; Sørensen, Christina & Pottinger, TG [Show all 10 contributors for this article] (2008). Behavioral plasticity in rainbow trout (Oncorhynchus mykiss) with divergent coping styles: When doves become hawks. Hormones and Behavior. ISSN 0018-506X. 54, p. 534–538. doi: 10.1016/j.yhbeh.2008.05.005. Full text in Research Archive
• Lastein, Stine; Höglund, Erik; Mayer, Ian; Øverli, Øyvind & Døving, Kjell Bjarne (2008). Female Crucian Carp, Carassius carassius, Lose Predator Avoidance Behavior when Getting Ready to Mate. Journal of Chemical Ecology. ISSN 0098-0331. 34(11), p. 1487–1491. doi: 10.1007/s10886-008-9553-9. Full text in Research Archive
• Korzan, Wayne J.; Höglund, Erik; Watt, Michael J.; Forster, Gina L.; Øverli, Øyvind & Lukkes, Jodi L. [Show all 7 contributors for this article] (2007). Memory of opponents is more potent than visual sign stimuli after social hierarchy has been established. Behavioural Brain Research. ISSN 0166-4328. 183, p. 3142–3142. Full text in Research Archive
• Höglund, Erik; Sørensen, Christina; Bakke, Marit J.; Nilsson, Gøran Erik & Overli, O (2007). Attenuation of stress-induced anorexia in brown trout (Salmo trutta) by pre-treatment with dietary L-tryptophan. British Journal of Nutrition. ISSN 0007-1145. 97. doi: 10.1017/S0007114507450280. Full text in Research Archive
• Schøyen, Hilde Faaland; Rouvinen-Watt, Kirsti; Höglund, Erik; Stone, K Peter & Skrede, Anders (2007). Effect of dietary bacterial protein or L-tryptophan supplementation on welfare and growth performance in silverfox Bacterial protein and tryptophan for silver fox. Canadian Journal of Animal Science. ISSN 0008-3984. 87(1), p. 93–102. Full text in Research Archive Show summary

  The suitability of bacterial protein meal as a feed ingredient in silver fox diets was examined in an experiment comprising 72 juvenile silver foxes. Bacterial protein meal has a high content of tryptophan, which is the precursor for the neurotransmitter serotonin. The biological hypothesis on which this study was premised was that increased brain serotonin production reduces the fear response, which may lead to better welfare and performance through lower energy expenditure related to fear-induced defensive responses. The effect of substituting 15% fish meal with bacterial protein meal was measured by two behavioural tests, growth performance and fur quality, by comparison with a control diet and a diet supplemented with a high level of synthetic tryptophan. The welfare of the foxes fed the diet supplemented with synthetic tryptophan was considered to be improved, as they used shorter time to approach feed in the presence of a person; thus displayed less fear, than the other two groups after treatment. Weight gain of the foxes during 55 d did not differ among diets, and feed consumption was similar. Live grading of the foxes showed that the dietary treatments did not affect fur quality (P > 0.05). It is concluded that 15% bacterial protein meal can replace fish meal in dry silver fox diets and that a large supplement of tryptophan reduces fear of silver foxes kept in cages.

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• Calabrese, Sara; Jonassen, Thor Magne; Steigum, Endre; Åsnes, Helga Øen; Imsland, Albert & Saude, Carolina Serra [Show all 8 contributors for this article] (2024). Corrigendum: Does sedation with AQUI-S^® mitigate transport stress and post transport mortality in ballan wrasse (Labrus bergyltae)? (Frontiers in Veterinary Science, (2024), 11, (1347062), 10.3389/fvets.2024.1347062). Frontiers in Veterinary Science. 11. doi: 10.3389/fvets.2024.1386051. Full text in Research Archive
• Calabrese, Sara; Höglund, Erik; Furseth, Kamilla; López, Iria Folgueira; MALTA, Erik & Bolhuis, Henk [Show all 9 contributors for this article] (2023). Replacing fish meal with fermented products- a diet trial with post-smolt Atlantic salmon. Full text in Research Archive
• Vindas, Marco Antonio; Gorissen, Marnix; Höglund, Erik; Flik, G.; Tronci, Valentina & Damsgård, Børge [Show all 11 contributors for this article] (2016). How do individuals cope with stress? A neuroendocrine substrate for proactive and reactive coping styles in fish. Full text in Research Archive
• Jane, Behrens; Höglund, Erik; Larsen, Bodil Katrine & Skov, Peter Vilhelm (2014). Temperature and oxygen as determining factors in post-stress recovery profiles of Norwegian lobster Nephrops norvegicus. Full text in Research Archive
• Jokumsen, Alfred; Höglund, Erik; Lund, Ivar; Madsen, Lone; Pedersen, Lars Flemming & Nielsen, Max [Show all 9 contributors for this article] (2014). Robustfish: New possibilities for growth and robustness in organic aquaculture. Full text in Research Archive
• Vindas, Marco Antonio; Folkedal, Ole; Johansen, Ida Beitnes; Kristiansen, Tore S; Stien, Lars Helge & Braastad, Bjarne Olai [Show all 9 contributors for this article] (2012). Frustrert fisk: Uforutsigbar utforing av laks gir økt aggresjon og påvirker hjernens belønnings-system. Full text in Research Archive
• Laursen, Danielle Caroline; Åberg-Andersson, Madelene; Silva, Patricia & Höglund, Erik (2012). Using preference testing to investigate the threshold for crowding in farmed rainbow trout Oncorhynchus mykiss. Full text in Research Archive
• Vindas, Marco Antonio; Höglund, Erik; Folkedal, Ole; Johansen, Ida Beitnes; Braastad, Bjarne Olai & Stien, Lars Helge [Show all 8 contributors for this article] (2012). Omission of expected reward sensitizes the brain dopaminergic system of classically conditioned Atlantic salmon. Full text in Research Archive
• Alvarado, Marco Antonio Vindas; Folkedal, Ole; Kristiansen, Tore S; Stien, Lars Helge; Braastad, Bjarne Olai & Mayer, Ian [Show all 8 contributors for this article] (2012). Effects of omission of expected reward on agonistic behaviour and dopaminergic activity of Atlantic salmon (Salmo salar). Full text in Research Archive
• Åberg-Andersson, Madelene; Silva, Patricia; Steffensen, John Fleng & Höglund, Erik (2012). Offspring characteristics in two rainbow trout Oncorhynchus mykiss lines selected for contrasting stress responsiveness. Full text in Research Archive
• Gjøen, Hans Magnus; Vaz, Jonathan Serrano; Øverli, Øyvind; Skaarud, Anders & Höglund, Erik (2010). New Tractable Selection Criteria for Disease Resistance and Animal Welfare in Fish. Full text in Research Archive Show summary

  Early variation in metabolic rate may predict other trait characteristics, such as social dominance, growth and timing of sexual maturation and stress responsiveness. This information could be used to optimize rearing regimes, before newly hatched fish enter more cost intensive parts of the production cycle, and also to increase the effectiveness selecting for these traits in a breeding program. Genetic parameters for four traits were investigated. The two new predicative traits, i.e. day-degrees and Swim- up time, showed high heritabilities of 0.41 and 0.38, respectively, but with large standard errors. The genetic correlation between the two new indicative traits and resistance against IPN was 0.41 and 0.60, respectively. Since the present method is much less laborious and cost-efficient than other methods for measuring stress response, it should be an attractable alternative selection criterion for disease resistance in many breeding programs. The present study has thus demonstrated the use of non-invasive and cost efficient new selection criteria for disease resistance and animal welfare. Further studies to establish more conclusive estimates of the genetic parameters are needed.

• Gjøen, Hans Magnus; Vaz, Jonathan Serrano; Øverli, Øyvind & Höglund, Erik (2010). Genetisk korrelasjon mellom stressresistens og ulike produksjonsegenskaper. Full text in Research Archive Show summary

  Tidligere studier av salmonider har indikert en sammenheng mellom utviklingshastighet, metabolsk rate og vekstpotensial, men det er fortsatt faglig uenighet om det er en direkte forbindelse mellom vekst i perioder med eksogent (ytre) og endogent fôring (indre, dvs plommesekk). Vi har i dette prosjektet vist at det hos laks er en slik sammenheng mellom utviklingshastighet i yngelstadiet og fremtidig vekstevne. Utviklingshastighet er da målt som tid fra klekking til startfôring i 100 familier fra Marine Harvest. Vi har også sett spesielt på tre tidlig klekte familier i forhold tre sent klekte mht oksygenopptak. Resultatet viser at de familiene som klekker sent har større egg og raskere utviklningshastighet. På annen laks som er hentet fra avlsprogrammet til AquaGen er det også undersøkt om det er forskjell i kortisol nivået hos rasktvoksende og sentvoksende individer, basert på tidligere tilvekst. Her fant en at de med størst veksthastighet hadde lavest kortisolnivå. Dette kan bety at det i kommersielt oppdrett vil være gunstig å sortere lakseyngel mht startfôringstidspunkt for å optimalisere fôringsregimet i senere stadier. Det vil også bli presentert genetiske korrelasjoner mellom ulike produksjonsegenskaper (tilvekst, tidlig kjønnsmoding, fett i filet, farge i filet og sykdomsresistens mot noen spesifikke sykdommer) og utviklingshastighet, målt som tid til klekking. Andre studier har indikert positiv sammenheng mellom stressmestringsevne og sykdomsresistens, både hos fisk og andre dyreslag. Dersom vi her får bekreftet en slik sammenheng vil en kunne benytte dette som et kostnadseffektivt seleksjonskriterium hos laks.

• Silva, Patricia; Øverli, Øyvind; Höglund, Erik & Martins, Catarina I.M. (2010). Stress coping styles in farmed tilapia (Oreochromis niloticus): Consistent individual behavioural differences and response to conspecific alarm cues. Full text in Research Archive
• Silva, Patricia; Martins, Catarina I.M.; Höglund, Erik & Øverli, Øyvind (2010). Stress coping styles in farmed tilapia (Oreochromis niloticus): Consistent individual behavioural differences and response to conspecific alarm cues. Full text in Research Archive
• Silva, Patricia; Pham, Khoi Dinh; Øverli, Øyvind; Höglund, Erik; Gjøen, Hans Magnus & Martins, Catarina I.M. (2010). How the smallest and the largest individuals in a fish group appraise an aggressive encounter. Full text in Research Archive
• Vaz, Jonathan Serrano; Åberg, Madelene; Gjøen, Hans Magnus; Steffensen, John Fleng & Höglund, Erik (2009). Larval developmental rate, metabolic rate and future growth performance in Atlantic salmon. Comparative Biochemistry and Physiology A. ISSN 1095-6433. p. 140–140. Full text in Research Archive
• Höglund, Erik & Vaz, Jonathan Serrano (2008). Larval developmental rate, stress responsiveness and life history traits in salmonids. Comparative Biochemistry and Physiology A. ISSN 1095-6433. p. 209–209. Full text in Research Archive
• Haraldstad, Tormod; Johansen, Kurt; Höglund, Erik & Korslund, Lars (2024). Overvåking av sjøørret i kystvassdrag langs Sørlandskysten. - Utvandringstidspunkt, sjøoverlevelse og livshistoriestrategier. NORCE Research AS. Full text in Research Archive
• Johansen, Kurt; Moland, Esben & Höglund, Erik (2019). The social-ecological value of recreational fishing for sea trout; a potential for further development of the experience industry in Aust-Agder? (TROUT XP). Norsk institutt for vannforskning (NIVA). ISSN 9788257770914. Full text in Research Archive Show summary

  Prosjektet undersøkte hvilken betydning det å få sjøørret har for fritidsfiskere i form av fiskeglede og videre hva som er viktig for en god fiskeopplevelse. Bakgrunnen for dette er å få i stand et europeisk samarbeid og en søknad omkring sosio-økologiske problemstillinger i kystsonen, med fokus på fritidsfiske og turisme. I samarbeid med Aust-Agder Jeger- og Fiskeforening ble det utviklet mobil- og internettapplikasjoner som rapporteringsverktøy. Resultatene av bruken av dette verktøyet viste at fiskeeffektiviteten blant deltagerne var 1 sjøørret pr 5,34 timer fisket og det var ingen signifikant forskjell i fornøydhet knyttet til utstyrsvalg eller om fiskeren fikk sjøørret eller ikke. Det var en positiv sammenheng mellom størrelsen på sjøørret fanget og fornøydhet hos fiskeren. Det betyr at når fiskeren får fisk, har størrelsen på fangsten innvirkning på hvor fornøyd fiskeren er med turen. 44% av sjøørreten som var over minstemålet ble sluppet ut igjen. Resultatene ble presentert på «Improved production strategies for endangered freshwater species (IMPRESS)» sitt EU-nettverksmøte i Arendal. Som referanseperson i prosjektet ble også professor Robert Arlinghaus IGB Leibniz-Institute of Freshwater Ecology and Inland Fisheries inkludert, en sentral europeisk forsker innen de sosiale og økologiske verdiene av fritidsfiske. Resultatene fra prosjektet har blitt diskutert med forskere fra Stockholms og Göteborgs Universitet, Danmarks Tekniske Universitet, og Leibniz-Institute of Freshwater Ecology and Inland Fisheries. Planen videre er å søke om midler til et Horizon 2020 COST forskernettverk med fokus på fritidsfiske.

• Hagen, Anders Gjørwad; Hytterød, Sigurd; Olstad, Kjetil; Garmo, Øyvind Aaberg; Darrud, Mari & Holter, Tobias Houge [Show all 12 contributors for this article] (2019). Effekter på laks (Salmo salar) ved eksponering for monokloramin. Norsk institutt for vannforskning (NIVA). ISSN 9788257770938. Full text in Research Archive Show summary

  Det er gjort flere eksperimentelle forsøk med formål å utvikle klor som behandling mot Gyrodactylus salaris i elver. Gjennom disse forsøkene er det funnet at svært lave konsentrasjoner av klor tilsatt som monokloramin, kan fjerne G. salaris fra laksunger i løpet av få dager uten å ha synlige negative effekter på laksen. Klor kan være giftig for fisk, og flere arter innenfor laksefamilien (Salmonidae) er beskrevet som svært følsomme for klor. Det er imidlertid stor variasjon i oppgitte konsentrasjoner for akutt giftighet. Kronisk giftighet for klor er observert etter eksponering for residualt klor helt ned i 3 μg/l, men da over en eksponeringsperiode på 12 uker. Hensikten med dette prosjektet har vært å undersøke om, og eventuelt hvordan, ettårige og toårige laksunger påvirkes av eksponering for klorkonsentrasjoner som er relevant for behandling mot parasitten. Det ble også undersøkt om fisken evner å restituere eventuelle subletale effekter fra kloreksponeringen. Eksponering for vann tilsatt 30 og 60 μg klor/l ga kun små blodfysiologiske forandringer hos fisken. Alle fysiologiske forandringene, med unntak av reduserte hematokritverdier hos gruppen med ettåringer, restituerte også raskt etter endt kloreksponering. Kloreksponeringen ga ingen patologiske forandringer i gjellene, og det ble ikke registrert vesentlige forskjeller i protein- og metabolittsammensetningen i slimlaget til kloreksponert fisk sammenlignet med kontrollfisk. Det var liten forskjell i fysiologisk effekt på laksungene som ble eksponert for de to klordosene. Dette gir en viss grad av fleksibilitet ved dosering av kloramin til et vassdrag, og lokale variasjoner i klorkonsentrasjon kan tolereres av fisken. Forsøket indikerer at laksunger kan eksponeres i inntil 17 dager for dobbelt så høy klordose som tidligere har vist seg å fjerne parasitten fra laks i løpet av 2-4 dager. En slik fleksibilitet representerer en robusthet for eventuell bruk av kloramin som behandlingskjemikalium mot G. salaris.

• Barlaup, Bjørn Torgeir; Skoglund, Helge; Pulg, Ulrich; Halvorsen, Godtfred A.; Velle, Gaute & Isaksen, Trond Einar [Show all 27 contributors for this article] (2018). Blekeprosjektet 2014-2017. NORCE Research AS. Full text in Research Archive Show summary

  Bleka i Byglandsfjorden er en relikt laks som gjennomfører hele livssyklusen i ferskvann. Dette gjør den til en av Norges mest spesielle fiskebestander med høy vernestatus. Bleka ble nesten utryddet av de samlede effektene av forsuring og vassdragsreguleringer på slutten av 1960-tallet, og den har siden vært avhengig av kultiveringstiltak. Målet for prosjektet er å reetablere en selvreproduserende blekebestand som ikke lenger er avhengig av utsettinger innen 2020.

• Haraldstad, Tormod; Güttrup, J. & Höglund, Erik (2016). Slep av laksesmolt fra Storelva som avbøtende tiltak mot estuarine blandsoner - Smoltårgang 2016. Norsk institutt for vannforskning (NIVA). ISSN 9788257768140. Full text in Research Archive Show summary

  I handlingsplanen for kalking av Storelva er estuarine blandsoner anført som en utfordring for laksebestanden i elva. Inntil videre betraktes fangst av nedvandrende smolt med påfølgende sleping ut fjorden som en del av kalkingsstrategien. Saliniteten i Nævestadfjorden våren 2016 var på et nivå der aluminium er på en slik tilstandsform at en forventer akkumulering på gjeller til utvandrende laksesmolt. Dette vil føre til redusert sjøoverlevelse til naturlig utvandrende smolt. Det ble derfor gjennomført syv slep med til sammen 1878 laksesmolt våren 2016. Det ble fanget laksesmolt ved to lokaliteter gjennom hele utvandringsperioden. Fangstene i elvemunningen er de høyeste siden 2009, mens fangstene ved Fosstveit er noe lavere. Lave fangster ved Fosstveit skyldes antagelig en betydelig innskrenking av gyte- og oppvekstområder oppstrøms på grunn av vandringshinderet som er etablert ved Nes Verk. Fangst og slep av laksesmolt er tidkrevende og krever personell med kunnskap og erfaring med denne type arbeid. Vi vil likevel anbefale dette som tiltak siden behandling av elvevannet med silikat vil være betydelig mer kostnadskrevende.

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