Introduction
Genetic variation is key in determining traits important for Atlantic salmon aquaculture, and selective breeding has been widely used to improve performance. However, environmental conditions such as nutrition, handling, disease exposure, temperature, and oxygen availability also significantly affect the development and health of fish. Increasing attention is being given to how the broodstock (G0) environment may influence the performance of their offspring (G1), including immune function and stress resilience. In Norwegian aquaculture, different rearing and maturation practices across breeding and multiplier companies may be contributing to variation in offspring health and robustness. Understanding these environmental influences is essential for improving fish welfare and production outcomes. As part of the project, EpiBrood , we explore how variations in broodstock rearing conditions affect immune and stress responses in the offspring of Atlantic salmon.
Materials and methods
Two major salmon egg producers provided experimental materials for this project. Eggs from Producer 1 originated from broodstock reared in southern and mid-Norway. In contrast, eggs from Producer 2 came from broodstock reared in three different locations: on-land and at-sea facilities in Norway, and an on-land facility in Iceland. Before the first feeding stage, the alevins were subjected to transport stress and a pathogen challenge. When fish from Producer 1 reached approximately 20 grams, they underwent a stress test. Additionally, head kidney leukocytes and hepatocytes were isolated, cultured, and exposed to various model stressors for further analysis.
Results
Alevins from Producer 1 showed no significant mortality following transport. However, after 24 hours, alevins originating from Mid-Norway had higher survival rates than those from South-Norway. Following exposure to Yersinia ruckeri , one Mid-Norway group demonstrated a higher survival rate than the other group. This difference was partially supported by gene expression profiles related to inflammation and antibacterial defence at mucosal sites. Upon exposure to handling and confinement stress, parr from Mid-Norway exhibited a higher cortisol response than parr from South-Norway. At the cellular level, exposure to stressors simulating oxidative stress, hypoxia, and bacterial infection revealed no consistent origin-dependent patterns.
Similarly, alevins from Producer 2 did not exhibit transport-related mortality. However, after 24 hours, alevins derived from Norwegian broodstock had higher survival rates than those from Icelandic broodstock. No clear differences were observed in gene expression profiles between the groups following pathogen exposure. Nonetheless, behavioural differences were noted among the groups.
Conclusion
The broodstock environment had variable effects on immune and stress responses of the offspring, with some physiological attributes showing origin-dependent differences. These findings suggest that parental rearing conditions can influence offspring robustness and should be considered in broodstock management strategies.
Acknowledgement
The study was financed by the Norwegian Seafood Research Fund (EpiBrood #901923) .