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Open Access Research article

Effects of environmental stress on mRNA expression levels of seven genes related to oxidative stress and growth in Atlantic salmon Salmo salar L. of farmed, hybrid and wild origin

Monica F Solberg12*, Bjørn Olav Kvamme3, Frank Nilsen2 and Kevin A Glover1

Author affiliations

1 Section of Population Genetics and Ecology, Institute of Marine Research, Nordnes, P.O. Box 1870, N-5817, Bergen, Norway

2 Department of Biology, University of Bergen, Box 7800, 5020, Bergen, Norway

3 Section of Health, Institute of Marine Research, Nordnes, P.O. Box 1870, N-5817, Bergen, Norway

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Citation and License

BMC Research Notes 2012, 5:672  doi:10.1186/1756-0500-5-672

Published: 5 December 2012

Abstract

Background

Ten generations of domestication selection has caused farmed Atlantic salmon Salmo salar L. to deviate from wild salmon in a range of traits. Each year hundreds of thousands of farmed salmon escape into the wild. Thus, interbreeding between farmed escapees and wild conspecifics represents a significant threat to the genetic integrity of wild salmon populations. In a previous study we demonstrated how domestication has inadvertently selected for reduced responsiveness to stress in farmed salmon. To complement that study, we have evaluated the expression of seven stress-related genes in head kidney of salmon of farmed, hybrid and wild origin exposed to environmentally induced stress.

Results

In general, the crowding stressor used to induce environmental stress did not have a strong impact on mRNA expression levels of the seven genes, except for insulin-like growth factor-1 (IGF-1) that was downregulated in the stress treatment relative to the control treatment. mRNA expression levels of glutathione reductase (GR), Cu/Zn superoxide dismutase (Cu/Zn SOD), Mn superoxide dismutase (Mn SOD), glutathione peroxidase (GP) and IGF-1 were affected by genetic origin, thus expressed significantly different between the salmon of farmed, hybrid or wild origin. A positive relationship was detected between body size of wild salmon and mRNA expression level of the IGF-1 gene, in both environments. No such relationship was observed for the hybrid or farmed salmon.

Conclusion

Farmed salmon in this study displayed significantly elevated mRNA levels of the IGF-1 gene relative to the wild salmon, in both treatments, while hybrids displayed a non additive pattern of inheritance. As IGF-1 mRNA levels are positively correlated to growth rate, the observed positive relationship between body size and IGF-1 mRNA levels detected in the wild but neither in the farmed nor the hybrid salmon, could indicate that growth selection has increased IGF-1 levels in farmed salmon to the extent that they may not be limiting growth rate.

Keywords:
Atlantic salmon; Farmed escapees; Introgression; Hybrid; Common garden; mRNA level; Insulin-like growth factor −1; Oxidative stress; Non additive inheritance