WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2025 69 cultures. Last, but not least, we already have the knowledge to work with redox effects of real challenges in fish farming on the more well-known responses. The take home message in this regard is that redox regulation is an important player in the overall metabolism of plants and animals, and that this knowledge should be taken into account also in fish biology studies. Notes Kristin Hamre,* Peng Yin, Takaya Saito and Per Gunnar Fjelldal, Institute of Marine Research, Bergen, Norway. * Corresponding author: post@kristinhamre.no Hamre Aquatic Nutrition, Breiviken 8, 5042 Bergen, Norway. References Diebold, L. and N. S. Chandel (2016). “Mitochondrial ROS regulation of proliferating cells.” Free Radic Biol Med 100: 86-93. Fjelldal, P. G., T. Saito, B. T. Björnsson, P. Yin, T. J. Hansen, A. Ø. Pedersen and K. Hamre (2024). “Exogenous growth hormone (GH) increases dimension and reduces strength of vertebrae in Atlantic salmon (Salmo salar).” Aquaculture 598, 741005. Hamre, K., G. Micallef, M. Hillestad, J. Johansen, S. Remo, W. X. Zhang, E. Odegard, P. Araujo, A. J. P. Philip and R. Waagbo (2022). “Changes in daylength and temperature from April until August for Atlantic salmon (Salmo salar) reared in sea cages, increase growth, and may cause consumption of antioxidants, onset of cataracts and increased oxidation of fillet astaxanthin.” Aquaculture 551. Hamre, K., W. Zhang, M. H. Austgulen, E. Mykkeltvedt, P. Yin, M. Berntssen, M. Espe and C. Berndt (2024). “Systemic and strict regulation of the glutathione redox state in mitochondria and cytosol is needed for zebrafish ontogeny.” Biochimica et Biophysica Acta (BBA) - General Subjects 1868(6). Jones, D. P. and H. Sies (2015). “The Redox Code.” Antioxidants & Redox Signaling 23(9): 734-746. Nordgarden, U., R. Ørnsrud, T. Hansen and G.-I. Hemre (2003). “Seasonal changes in selected muscle quality parameters in Atlantic salmon (Salmo salar L:) reared under natural and continuous light.” Aquaculture Nutrition 9: 161-168. Sies, H. (2017). “Hydrogen peroxide as a central redox signaling molecule in physiological oxidative stress: Oxidative eustress.” Redox Biology 11: 613-619. Yin, P., B. T. Bjornsson, P. G. Fjelldal, T. Saito, S. C. Remo, R. B. Edvardsen, T. Hansen, S. Sharma, R. E. Olsen and K. Hamre (2022). “Impact of Antioxidant Feed and Growth Manipulation on the Redox Regulation of Atlantic Salmon Smolts.” Antioxidants 11(9). Yin, P., T. Saito, P. G. Fjelldal, B. T. Bjornsson, S. C. Remo, T. J. Hansen, S. Sharma, R. E. Olsen and K. Hamre (2023). “Seasonal Changes in Photoperiod: Effects on Growth and Redox Signaling Patterns in Atlantic Salmon Postsmolts.” Antioxidants (Basel) 12(8). Yin, P., T. Saito, P. G. Fjelldal, B. T. Björnsson, S. C. Remø, S. Sharma, R. E. Olsen and K. Hamre (2024). “Environmentally driven changes in Atlantic salmon oxidative status interact with physiological performance” Aquaculture 581. FIGURE 5. Photoperiod-driven redox responses in Atlantic salmon postsmolts. A. Specific growth rate (SGR) follows the daylength and liver vitamin C concentration is lowered when daylength and SGR increase and increases back to early spring levels when daylength and SGR decrease in late summer. B. Expression of the redox transcription factors nrf2 and keap1 follow similar curves (Yin, Saito et al. 2023). FIGURE 6. Seasonal changes of redox homeostasis in Atlantic Salmon postsmolts exposed to simulated natural changes in daylength and water temperature during spring and summer. A. Muscle vitamin C and E, and liver GSH and MDA. B. Expression of muscle and liver redox sensitive genes which follow similar curves as the antioxidants (Yin, Saito et al. 2024). Future approach to understand redox biology in fish is, of course, to first look into literature from other species. Because fish farming has special conditions and topics, a second direction is to validate biomarkers. This could be achieved through experiments with the candidate species, but since farmed species are big and usually have a long lifespan, such experiments will be costly. A good alternative to unravel the principles is to use model species like zebrafish or fish-cell cultures. Last, but not least, we already have the knowledge to work with redox effects of real challenges in fish farming on the more well-known responses. The take home message in this regard is that redox regulation is an important player in the overall metabolism of plants and animals, and that this knowledge should be taken into account also in fish biology studies.
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