Stress In Salmon Research Articles

The behavioral and neurobiological response to sound stress in salmon.

Noise associated with human activities in aquatic environments can affect the physiology and behavior of aquatic species which may have consequences at the population and ecosystem levels. Low frequency sound is particularly stressful for fish, since it is an important factor in predator-prey interactions. Even though behavioral and physiological studies have been conducted to assess the effects of sound on fish species, neurobiological studies are still lacking. In this study we exposed farmed salmon to low frequency sound for 5 minutes a day for 30 trials and conducted behavioral observations and tissue sampling before sound exposure (timepoint zero; T0) and after 1 (T1), 10 (T2), 20 (T3) and 30 (T4) exposures, to assess markers of stress. These included plasma cortisol, neuronal activity, monoaminergic signaling, and gene expression in 4 areas of the forebrain. We found that sound exposure induced an activation of the stress response by eliciting an initial startle behavioral response, together with increased plasma cortisol levels and a decrease in neuronal activity in the hypothalamic tubercular nuclei (TN). At T3 and T4 salmon showed a degree of habituation in their behavioral and cortisol response. However, at T4, salmon showed signs of chronic stress with increased serotonergic activity levels in the dorsolateral and dorsomedial pallium, the preoptic area, and the TN, as well as an inhibition of growth and reproduction transcripts in the TN. Together, our results suggest that prolonged exposure to sound results in chronic stress that leads to neurological changes which suggest a reduction of life fitness traits.

Characterization and transcript expression analyses of four Atlantic salmon (Salmo salar) serpinh1 paralogues provide evidence of evolutionary divergence

Atlantic salmon (Salmo salar) are not only the world’s most economically important farmed fish in terms of total value, but also a salmonid, which means that they are invaluable for studies of the evolutionary fate of genes following multiple whole-genome duplication (WGD) events. In this study, four paralogues of the molecular chaperone serpinh1 were characterized in Atlantic salmon, as while this gene is considered to be a sensitive biomarker of heat stress in salmonids, mammalian studies have also identified it as being essential for collagen structural assembly and integrity. The four salmon paralogues were cloned and sequenced so that in silico analyses at the nucleotide and deduced amino acid levels could be performed. In addition, qPCR was used to measure: paralogue- and sex-specific constitutive serpinh1 expression across 17 adult tissues; and their expression in the liver and head kidney of male Atlantic salmon as affected by stress phenotype (high vs. low responder), increased temperature, and injection with a multi-valent vaccine. Compared to the other three paralogues, serpinh1a-2 had a unique constitutive expression profile across the 17 tissues. Although stress phenotype had minimal impact on the transcript expression of the four paralogues, injection with a commercial vaccine containing several formalin inactivated bacterins increased the expression of most paralogues (by 1.1 to 4.5-fold) across both tissues. At 20 °C, the expression levels of serpinh1a-1 and serpinh1a-2 were generally lower (by −1.1- to −1.6-fold), and serpinh1b-1 and serpinh1b-2 were 10.2- to 19.0-fold greater, in comparison to salmon held at 12 °C. With recent studies suggesting a putative link between serpinh1 and upper thermal tolerance in salmonids, the current research is a valuable first step in elucidating the potential mechanisms involved. This research: supports the use of serpinh1b-1 and serpinh1b-2 as a biomarkers of heat stress in salmon; and provides evidence of neo- and/or subfunctionalization between the paralogues, and important insights into how multiple genome duplication events can potentially lead to evolutionary divergence.

Reduced water quality associated with higher stocking density disturbs the intestinal barrier functions of Atlantic salmon (Salmo salar L.)

The stocking density of fish in aquaculture is of major importance as it may have profound effects on water quality resulting in impact on fish health and possibly affect the external barriers that protect against pathogens There are many husbandry conditions, including stocking density, that may affect the primary protective barriers, i.e. the skin, intestine and gills, against invading pathogens and other harmful substances. It is well known that increased fish density will lead to decreased dissolved oxygen (DO) levels and affect other water quality parameters such as carbon dioxide, pH and ammonia. It is not known if such changes in the rearing environment affect the intestinal primary barriers of Atlantic salmon. Groups of Atlantic salmon post-smolts were kept for 57 days in tanks supplied with seawater at a constant flow at stocking densities of 10, 30, 50 and 70 kg m−3; reduced water quality was associated with higher stocking density. Repeated sampling for plasma cortisol and water cortisol release rate indicate that the highest stocking density elicited a primary stress response in the fish, which decreased with time. The physical intestinal barrier was assessed using paracellular permeability measurements, i.e. transepithelial electrical resistance (TER) and diffusion rate of 14C-mannitol, in combination with the translocation rate of heat-inactivated Aeromonas salmonicida. The physical intestinal barrier decreased with increasing density, both when measured as decreased transepithelial electrical resistance and as elevated paracellular permeability for 14C-mannitol. As this was observed at a time point when no differences could be seen in plasma cortisol or cortisol release rate, it suggests that intestinal paracellular permeability can be a useful marker for chronic stress in salmon. The status of the intestinal immune system was assessed as degree of neutrophil infiltration as well as the mRNA expression of the pro-inflammatory cytokines, interferon γ (IFNγ), interleukin (IL) 1β and tumor necrosis factor (TNF) α, anti-inflammatory cytokines, IL-10 and transforming growth factor β (TGFβ) and other immune related-genes, IL-8 and the inhibitor of the transcription factor nuclear factor κB (IκB). The intestinal immune system was affected at the highest stocking density as observed by a decreased expression of IFNγ in parallel with higher infiltration of neutrophils. In conclusion, high stocking density associated with reduced water quality is chronically stressful to the fish as it elicits a primary stress response as well as a weakened physical and disturbed immunological primary barrier.

Developing specific molecular biomarkers for thermal stress in salmonids

BackgroundPacific salmon (Oncorhynchus spp.) serve as good biological indicators of the breadth of climate warming effects on fish because their anadromous life cycle exposes them to environmental challenges in both marine and freshwater environments. Our study sought to mine the extensive functional genomic studies in fishes to identify robust thermally-responsive biomarkers that could monitor molecular physiological signatures of chronic thermal stress in fish using non-lethal sampling of gill tissue.ResultsCandidate thermal stress biomarkers for gill tissue were identified using comparisons among microarray datasets produced in the Molecular Genetics Laboratory, Pacific Biological Station, Nanaimo, BC, six external, published microarray studies on chronic and acute temperature stress in salmon, and a comparison of significant genes across published studies in multiple fishes using deep literature mining. Eighty-two microarray features related to 39 unique gene IDs were selected as candidate chronic thermal stress biomarkers. Most of these genes were identified both in the meta-analysis of salmon microarray data and in the literature mining for thermal stress markers in salmonids and other fishes. Quantitative reverse transcription PCR (qRT-PCR) assays for 32 unique genes with good efficiencies across salmon species were developed, and their activity in response to thermally challenged sockeye salmon (O. nerka) and Chinook salmon (O. tshawytscha) (cool, 13–14 °C and warm temperatures 18–19 °C) over 5–7 days was assessed. Eight genes, including two transcripts of each SERPINH1 and HSP90AA1, FKBP10, MAP3K14, SFRS2, and EEF2 showed strong and robust chronic temperature stress response consistently in the discovery analysis and both sockeye and Chinook salmon validation studies.ConclusionsThe results of both discovery analysis and gene expression showed that a panel of genes involved in chaperoning and protein rescue, oxidative stress, and protein biosynthesis were differentially activated in gill tissue of Pacific salmon in response to elevated temperatures. While individually, some of these biomarkers may also respond to other stressors or biological processes, when expressed in concert, we argue that a biomarker panel comprised of some or all of these genes could provide a reliable means to specifically detect thermal stress in field-caught salmon.

Heat shock proteins are not sensitive indicators of hatchery stress in salmon

Abstract An array of physiological, endocrinological, biochemical and behavioral indicators have been investigated for utility in assessing the level of stress imposed on cultured finfish by rearing conditions and husbandry practices. In the present report, juvenile Atlantic salmon (Salmo salar) were exposed to common forms of hatchery stress and the response of heat shock proteins (hsp) 30, 70 and 90 were measured as possible indicators of stress. Treatments included exposure to two types of anesthesia (tricaine methanesulfonate and 2-phenoxyethanol), formalin, hypoxia, hyperoxia, capture stress, crowding, feed deprivation and cold stress. Exposure of fish to heat stress at 26 °C (ΔT=11 °C) served as a positive control, and untreated fish were used as a negative control. Total RNA was isolated from gill tissue following treatment, and subjected to Northern analysis with cDNA probes specific to the three hsps. Hsp70 and Hsp90 mRNA levels increased three-fold and two-fold above control levels, respectively, following 15-min heat stress. hsp30 mRNA levels were unaffected by 15-min exposure to heat stress, but increased two-fold over control levels following 30-min exposure. In contrast, Hsp mRNA was not upregulated in response to the different hatchery stresses examined. Although cold stress, crowding and capture stress caused an increase in hsp90 mRNA levels, these were not significant. The findings suggest that hsp30, hsp70 and hsp90 are not sensitive indicators of hatchery stress in Atlantic salmon.

Cloning and characterization of salmon hsp90 cDNA: upregulation by thermal and hyperosmotic stress.

Accumulating evidence suggests that glucocorticoids are essential for development of hypoosmoregulatory capacity in salmon during adaptation to seawater. Heat shock protein (hsp)90 has been reported to function in signal transduction and the maturation and affinity of glucocorticoid receptors. We sought to determine whether this hsp might be upregulated by thermal and hyperosmotic stress in salmon, a species that migrates between the freshwater and marine environments. A 2625-bp cDNA cloned from a salmon cDNA library was found to code for a protein of 722 amino acids exhibiting a high degree of identity with zebra fish (92%) and human (89%) hsp90beta. Accumulation of hsp90 mRNA was observed in isolated branchial lamellae incubated under hyperosmotic conditions and in branchial lamellae of salmon exposed to hyperosmotic stress in vivo. In contrast, exposure of kidney to hyperosmotic stress in vitro and in vivo failed to elicit an increase in the quantity of hsp90 mRNA. By way of comparison, accumulation of hsp90 mRNA was observed in both branchial lamellae and kidney tissue subjected to thermal stress in vitro and in vivo. Western blot analyses of proteins isolated from tissues under identical conditions in vitro revealed that the pool of hsp90 increased with thermal stress but not with osmotic stress. The results suggest that accumulation of hsp90 mRNA in response to osmotic stress is unrelated to cellular protein denaturation and that synthesis of hsp90 may be regulated at both the level of transcription and translation.

Stress Response of Coho Salmon (Oncorhynchus kisutch) Elicited by Cadmium and Copper and Potential Use of Cortisol as an Indicator of Stress

Exposure of juvenile coho salmon (Oncorhynchus kisutch) to copper (Cu) produced a marked, dose-dependent serum cortisol elevation. Treatment with cadmium (Cd) did not elicit a cortisol elevation, even in moribund fish. Stressing salmon with sublethal levels of Cu or handling plus close confinement resulted in "ideal" compensation (return to prestress levels) in cortisol titers. Salmon exposed to Cu had depressed serum chloride levels and reduced survival when challenged with salt water. Exposure to Cd did not influence serum chloride or the ability to tolerate salt water. Handling and close confinement produced the same cortisol elevation in controls as in Cu- or Cd-treated fish, but exposure to Cu reduced the ability of the fish to survive the stress of handling and confinement. Cortisol level and other characteristics of the General Adaptation Syndrome of stress should not be universally applied as indicators of stress in salmon. Key words: stress, cortisol, heavy metals, coho salmon, Oncorhynchus kisutch, saltwater adaptation, stress resistance, stress indicator, cadmium, copper