Investigating the biological relevance of measuring gastrointestinal cortisol metabolite levels to assess stress responses in Atlantic salmon (Salmo salar L.) after an acute stress.

Monitoring stress levels of farmed Atlantic salmon (Salmo salar) is important to ensure fish welfare and optimize farm operations. Feces could be a promising matrix for assessing stress responses in fish, based on their properties of low-invasive sampling and allowing repeated sampling over time. Meanwhile, elevated levels of cortisol metabolites (CMs) in feces indicate the increases in plasma cortisol levels (PLA) after exposure to acute stress.

Molecular quantification of parasitic sea louse larvae depends on species and life stage.

Sea lice cause substantial economic and environmental harm to Norway's aquaculture industry and wild salmonid populations. Rapid, accurate quantification of lice larval densities in coastal waters remains the greatest bottleneck for providing empirical data on infestation risk within wild salmon habitats and aquaculture production regions. We evaluated the capability of droplet digital PCR (ddPCR) as an absolute quantification method for the planktonic stages of two parasitic louse species, Lepeophtheirus salmonis (Krøyer) and Caligus elongatus (von Nordman).

Data for characterization of the optical properties of Atlantic salmon (Salmo salar) blood.

Photoplethysmography is a recent addition to physio-logging in Atlantic salmon which can be used for pulse oximetry provided that the properties for light propagation in salmon tissues are known. In this work, optical properties of three constituents of Atlantic salmon blood have been characterized using a photo spectrometer in the VIS-NIR range (450-920 nm). Furthermore, Atlantic salmon blood cell size has been measured using a Coulter counter as part of light scattering property evaluations.

Large-effect loci mediate rapid adaptation of salmon body size after river regulation.

Understanding the potential of natural populations to adapt to altered environments is becoming increasingly relevant in evolutionary research. Currently, our understanding of adaptation to human alteration of the environment is hampered by lack of knowledge on the genetic basis of traits, lack of time series, and little or no information on changes in optimal trait values. Here, we used time series data spanning nearly a century to investigate how the body mass of Atlantic salmon () adapts to river regulation.

Early-season brown trout (Salmo trutta) migrants grow and survive better at sea.

The timing of seaward migration is a key life-history trait for many anadromous fish species, with growth and survival at sea depending on a match/mismatch scenario between the timing of the sea entry and optimal conditions. Based on a 25-year study with 15,226 individually tagged brown trout (Salmo trutta) in a Norwegian river, we analysed how the within-season timing of sea migration impacted growth and survival. In both first-time and veteran migrants, marine growth was highest for early migrating individuals, large individuals, and those with a low condition factor when entering the sea.

Redefining the oceanic distribution of Atlantic salmon.

Determining the mechanisms driving range-wide reductions in Atlantic salmon marine survival is hindered by an insufficient understanding of their oceanic ecology and distribution. We attached 204 pop-up satellite archival tags to post-spawned salmon when they migrated to the ocean from seven European areas and maiden North American salmon captured at sea at West Greenland. Individuals migrated further north and east than previously reported and displayed increased diving activity near oceanographic fronts, emphasizing the importance of these regions as feeding areas.

Factors influencing return rate and marine residence duration in sea trout populations in Central Norway.

Brown trout (Salmo trutta) display extensive plasticity in marine migratory behaviours, with marine migrations considered to be an adaptive strategy which enables sea trout to maximize growth and reproductive potential. However, marine migrations are not without associated costs, including threats posed by ever-increasing salmon lice (Lepeophtheirus salmonis) infestations. In the present study, we used passive integrated transponder technology to characterize variability in sea trout migration behaviour amongst three catchments situated in a region of intensive salmon farming in central Norway.

Repeatable individual variation in migration timing in two anadromous salmonids and ecological consequences.

Consistent individual differences in behavior have been demonstrated for many animals, but there are few studies of consequences of such repeated behavior in the wild. We tested consistency in migration timing to and from the sea among anadromous Arctic char () and brown trout (), using data from a study period of about 25 years, including more than 27,000 uniquely Carlin-tagged individuals that migrated to sea for feeding in the spring and returned to the river in late summer for up to 13 successive years. Consistency was found between individuals across time in timing of the seaward migration.

Effects of environmental enrichment on forebrain neural plasticity and survival success of stocked Atlantic salmon.

Fish reared for stocking programmes are severely stimulus deprived compared with their wild conspecifics raised under natural conditions. This leads to reduced behavioural plasticity and low post-release survival of stocked fish. Environmental enrichment can have positive effects on important life skills, such as predator avoidance and foraging behaviour, but the neural mechanisms underpinning these behavioural changes are still largely unknown.

Sea trout adapt their migratory behaviour in response to high salmon lice concentrations.

Sea trout face growth-mortality trade-offs when entering the sea to feed. Salmon lice epizootics resulting from aquaculture have shifted these trade-offs, as salmon lice might both increase mortality and reduce growth of sea trout. We studied mortality and behavioural adaptations of wild sea trout in a large-scale experiment with acoustic telemetry in an aquaculture intensive area that was fallowed (emptied of fish) synchronically biannually, creating large variations in salmon lice concentrations.

The Phe362Tyr mutation conveying resistance to organophosphates occurs in high frequencies in salmon lice collected from wild salmon and trout.

The parasitic salmon louse, and its resistance to chemical delousing agents, represents one of the largest challenges to the salmon aquaculture industry. We genotyped lice sampled from wild salmon and sea trout throughout Norway with the recently identified Phe362Tyr mutation that conveys resistance to organophosphates. These results were compared to data from lice sampled on farmed salmon in the same regions.

Passing a seawater challenge test is not indicative of hatchery-reared Atlantic salmon Salmo salar smolts performing as well at sea as their naturally produced conspecifics.

Despite satisfactory reactions to seawater challenge tests indicative of appropriate physiological state, hatchery-reared Atlantic salmon Salmo salar smolts stocked in the Eira River in Norway between 2001 and 2011 performed less well at sea in terms of growth, age at maturity and survival than smolts of natural origin. The mean rates of return to the river for hatchery-reared and naturally produced S. salar were 0·98 and 2·35%.

Atlantic salmon (Salmo salar L.) smolts require more than two weeks to recover from acidic water and aluminium exposure.

The detrimental effects of acid rain and aluminium (Al) on salmonids have been extensively studied, yet knowledge about the extent and rate of potential recovery after exposures to acid and Al episodes is limited. Atlantic salmon smolts in freshwater (FW) were exposed for 2 and 7-day episodes (ACID2 and ACID7, respectively) to low pH (5.7±0.

Impact of early salmon louse, Lepeophtheirus salmonis, infestation and differences in survival and marine growth of sea-ranched Atlantic salmon, Salmo salar L., smolts 1997-2009.

The impact of salmon lice on the survival of migrating Atlantic salmon smolts was studied by comparing the adult returns of sea-ranched smolts treated for sea lice using emamectin benzoate or substance EX with untreated control groups in the River Dale in western Norway. A total of 143 500 smolts were released in 35 release groups in freshwater from 1997 to 2009 and in the fjord system from 2007 to 2009. The adult recaptures declined gradually with release year and reached minimum levels in 2007.

Impact of parasites on salmon recruitment in the Northeast Atlantic Ocean.

Parasites may have large effects on host population dynamics, marine fisheries and conservation, but a clear elucidation of their impact is limited by a lack of ecosystem-scale experimental data. We conducted a meta-analysis of replicated manipulative field experiments concerning the influence of parasitism by crustaceans on the marine survival of Atlantic salmon (Salmo salar L.).

A critical life stage of the Atlantic salmon Salmo salar: behaviour and survival during the smolt and initial post-smolt migration.

The anadromous life cycle of Atlantic salmon Salmo salar involves long migrations to novel environments and challenging physiological transformations when moving between salt-free and salt-rich waters. In this article, (1) environmental factors affecting the migration behaviour and survival of smolts and post-smolts during the river, estuarine and early marine phases, (2) how behavioural patterns are linked to survival and (3) how anthropogenic factors affect migration and survival are synthesized and reviewed based on published literature. The timing of the smolt migration is important in determining marine survival.

Early marine migration of European silver eel Anguilla anguilla in northern Norway.

To study the migratory behaviour in wild northern European silver eel Anguilla anguilla during sea entry and early marine migration, 32 individuals were tagged with acoustic transmitters and registered at four automatic listening station arrays from the mouth of the north Norwegian River Alta and throughout the Alta Fjord. The A. anguilla entered the fjord during all parts of the tidal cycle and did not seem to utilize the outgoing tidal currents.

Does river of origin influence the early marine migratory performance of Salmo salar?

The early marine migratory behaviour of two populations of hatchery-reared Atlantic salmon Salmo salar was compared in a common-garden experiment. Post-smolts from a river in a long fjord (Laerdal River, 144 km from the open coastline, n = 79) and a short fjord (Flekke River, 20 km from the open coastline, n = 80) in western Norway were tagged with acoustic transmitters and released during the spring of 2005 and 2006 in the inner part of the Hardangerfjord system (Opo River mouth, 179 km from the open coastline). The migratory behaviour of the tagged fish was monitored by acoustic listening stations in the fjord system up to 167 km from the release site.

Effects of the fungicide azoxystrobin on Atlantic salmon (Salmo salar L.) smolt.

Atlantic salmon smolts were exposed to three doses of the fungicide azoxystrobin for 4 days, and physiological blood parameters and transcriptional effects in liver and muscle were evaluated in search for potential negative effects. Azoxystrobin exposure mediated up-regulation of catalase, MAPK1 and IGFBP1 in liver tissue. Catalase, transferrin, IGFBP1 and TNFR were up-regulated and CYP1A down-regulated in muscle tissue.

Effects of the sea louse Lepeophtheirus salmonis on temporal changes in cortisol, sex steroids, growth and reproductive investment in Arctic charr Salvelinus alpinus.

Groups of mature (5+ year old) Arctic charr Salvelinus alpinus held in sea water were exposed for 34 days to either a high (mean +/-s.e. 0.

Effects of acidic water and aluminum exposure on gill Na(+), K(+)-ATPase alpha-subunit isoforms, enzyme activity, physiology and return rates in Atlantic salmon (Salmo salar L.).

Na(+), K(+)-ATPase (NKA) is involved, through its role as a major driving force for electrochemical gradients, in a range of transmembrane transport processes. Maintenance of homeostasis in anadromous salmonids requires modulation of several gill ion secretory proteins as part of the preparatory adaptation and acclimation to marine life. Atlantic salmon smolts were exposed to combinations of low pH and inorganic aluminum (acid/Al(i)) in freshwater (FW) and were then transferred to seawater (SW) for studies of post-smolt performance.

Influence of sea temperature and initial marine feeding on survival of Atlantic salmon Salmo salar post-smolts from the Rivers Orkla and Hals, Norway.

The abundance of returning adult Atlantic salmon Salmo salar, in the River Orkla in mid-norway (1 sea-winter, SW, fish) and River Hals in north Norway (1-3 SW fish), was tested against the early marine feeding and the seawater temperature experienced by their corresponding year classes of post-smolts immediately after entry into the Trondheimsfjord (Orkla smolts, 22 years of data) and Altafjord (Hals smolts, 17 years of data). In both river-fjord systems, there was a significant positive correlation between the abundance of returning S. salar and the mean seawater temperature at the time of smolts descending to the sea.

Temporal and spatial variations in lice numbers on salmon farms in the Hardanger fjord 2004-06.

The long and narrow Hardanger fjord in western Norway has a high density of salmon farms and has had severe salmon lice, Lepeophtheirus salmonis, problems. In the years 2004-06, salmon lice numbers were recorded in selected salmon farms in the fjord as part of a larger research project. Most farm sites participated in a strategic control programme and were deloused between November and January in each year.

Effects of subchronic exposure to aluminium in acidic water on bioenergetics of Atlantic salmon (Salmo salar).

Atlantic salmon (Salmo salar) were exposed for 36 days to water from the acidified (pH 5.2) Fossbekk River (Norway) with 50 micro x L(-1) of aluminium (Al) added as AlCl(3), or to circumneutral water (pH 6.6) from Ims River (Norway).