dc.description.abstract | The salmonids in today’s Norwegian aquaculture are exposed to many stressors, like
suboptimal water quality, crowding and handling. This project focuses on red blood cell
(RBCs) function in Atlantic salmon and how cellular responses are affected by stress. Since
fish RBCs are nucleated and can change their gene expression, one of the main goals of this
thesis is to better understand how the RBCs function in the fight against viruses after the fish
have been exposed to handling stress. Lastly, one also wants to find a better way to monitor
stress levels in Atlantic salmon RBCs by testing and finding stress biomarkers.
A small in vivo stress trial was run, where Atlantic salmon were exposed to acute and chronic
handling stress. There were no long-lasting significant changes in stress hormones,
haemoglobin levels, or antiviral responses to poly (I:C) in the RBCs when measured after 1
and 4 days. However, the acute stress group had a trend towards higher blood plasma cortisol
level and the RBCs had a lower antiviral response to poly (I:C) than samples with lower
blood plasma cortisol.
Because of the unconclusive in vivo results, ex vivo trials with cultures of Atlantic salmon
RBCs were run to try and find more stable stress biomarkers. Stimulation with the chronic
stress hormone hydrocortisone showed an upregulation in gene expression of FkBP prolyl
isomerase 1 (FkBP1). For the in vivo stress trial samples, the gene expression of FkBP1 was
not upregulated in the RBCs for the stress groups, probably due to the low hormone levels
upon sampling.
Cultures of Atlantic salmon RBCs were also stimulated with isoproterenol and epinephrine in
hope of finding acute stress biomarkers. There was a significant increase in gene expression
of carbonic anhydrase 1 (Cahz) in response to isoproterenol, and heat-shock protein
(HSP)90aa in response to epinephrine.
In this ex vivo trial, Atlantic salmon RBCs were also stimulated with poly (I:C) to test the
effects of stress hormones on antiviral responses. The response to poly (I:C) on the gene
expression of the antiviral proteins ISG15, Mx1 and IRF3 was affected oppositely by acute
and chronic stress hormones. Acute stress led to an enhancement, and chronic stress to an
inhibition of the expression of these antiviral proteins. RBCs stimulated with both an acute
and a chronic stress hormone, indicated that chronic stress hormone effects are stronger than
acute stress hormone effects, as the antiviral responses still were inhibited.
In summary, these results strengthen the foundation for being able to monitor the chronic
stress levels of the fish in the field using low invasive blood sampling. The data from ex vivo
trials also indicate that chronic stress results in inhibition of antiviral responses in red blood
cells of Atlantic salmon, possibly making the fish more susceptible to systemic viral disease | en_US |