Current approaches in decoding the molecular mechanisms of long-term stress in adult farmed Atlantic salmon (Salmo salar)

Aquaculture sustainability and profit is highly dependent on good welfare for farmed fish including the economically important species Atlantic salmon (Salmo salar). Welfare is closely linked to stress, as prolonged stressful farming conditions can translate into reduced performance and health. Understanding how Atlantic salmon responds to aquaculture-related stressors has for the past years been a key focus area of research. Present review evaluates the current state of the art by assessing a defined panel of 13 recent articles on the topic. Particular attention is paid to methodological approaches and challenges in investigating chronic stress effects. Stress experiments are performed in profoundly different ways based on scientific interest, and applied stressors range from environmental challenges, for example water quality, to management-related practices and dietary stress. We show that majority of studies are limited to analysis at the transcriptional level. Quantitative reverse transcription PCR (RT-qPCR) is the dominating technology, followed by microarray assays. Post-translational studies are rare, and correlations between changes in transcript expressions and protein levels are generally not explored. We encourage future research to address this knowledge gap, as insight on proteome status may unravel more long-standing physiological mechanisms towards stress, for example tertiary effects, that can only be postulated by transcriptional analyses. Attention should also be paid to regulatory mechanisms operating on pre- and post-translational levels, for example microRNAs, which may be affected by environmental challenges and play roles in modifying stress responses.