Introduction
One of the main concerns for the environment due to salmon commercial aquaculture are salmon escapees (Keyser et al., 2018; Besnier et al., 2022). Escapees, breeding with wild conspecifics (Diserud et al., 2022) , have the potential to endanger local wild populations by introducing genetic changes that may be maladaptive in nature (Besnier et al., 2022) . Induced triploidization has been adopted as a strategy to provoke sterility in commercialy farmed Atlantic salmon. However, triploid salmon have shown reduced performance and welfare in commercial settings (Madaro et al., 2021, Stien et al., 2023) . This has been suggested to be due to farming suboptimal conditions and impaired stress coping capacity. The aim of this study was to compare physiological responses of diploid and triploid salmon siblings subjected to unpredictable chronic stress .
Materials and methods
Atlantic salmon were reared at the Institute of Marine Research (IMR, Matre, Norway). D iploid and triploid Atlantic salmon were subjected to a 21- days unpredictable chronic stress (UCS) regime and compared with fish that were not stressed. The UCS regime involved exposure of fish to seven unpredictable stressors two times a day . At the end of this period all groups were tested with an acute stressor (netting and transfer in a new tank) . B lood chemistry and selected pituitary genes expression were used to assess the stress response. Plasma parameters were sampled before (0) and 15 , 30 , 45, 60, 90, 120, 240, 300 min post-stress and included measurements of plasma ACTH, cortisol, ions, and metabolites. Gene expression analyses were performed at 0, 30, 60, 120, 240 min post-stress.
Results
Circulating level of ACTH (Fig 1a) and cortisol (Figure 1b) were significantly affected by fish ploidy (diploid vs triploid), type of treatment and time. After the stress test, plasma ACTH levels were mostly higher for triploid than for diploid in both UCS and naïve fish. While pre-stress levels of cortisol were similar between ploidy in both treatments, plasma cortisol levels increased predominantly in both UCS and control triploid groups. More results will be presented at the EAS conference in Vienna (Austria, 2023).
Discussion
T he two salmon ploidy groups showed noteworthy differences in the stress response. Post-stress ACTH and c ortisol release in plasma were generally higher in both triploid groups. Also, triploid fish showed wider post-stress fluctuations in most of the other plasma parameters. In addition, there were noteworthy ploidy differences in the expression of genes regulating the stress response at the pituitary levels. The study will be discussed in more detail at the EAS conference of Vienna ( Austria, 2023).
Funding
This study was part of the NRS TripWell-projected funded by Norway Royal Salmon.
References
-Besnier , F. et al. (2022) ‘Introgression of domesticated salmon changes life history and phenology of a wild salmon population’, Evolutionary Applications, 15(5), pp. 853–864.
-Diserud , O.H. et al. (2022) ‘Natural and anthropogenic drivers of escaped farmed salmon occurrence and introgression into wild Norwegian Atlantic salmon populations’, ICES Journal of Marine Science, 79(4), pp. 1363–1379.
- Keyser, F. et al. (2018) ‘Predicting the impacts of escaped farmed Atlantic salmon on wild salmon populations’, Canadian Journal of Fisheries and Aquatic Sciences , 75(4), pp. 506–512.
- Madaro, A. et al. (2021) ‘A comparison of triploid and diploid Atlantic salmon ( Salmo salar ) performance and welfare under commercial farming conditions in Norway’, Journal of Applied Aquaculture, pp. 1–15. Available at: https://doi.org/10.1080/10454438.2021.1916671.
- Stien, L.H., mfl, Production, fasting and delousing of triploid and diploid salmon in Northern Norway – Report for the 2020-generation. Rapport fra havforskningen 2023-20.