WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2025 31 recommended level of 4 g/kg phosphorus throughout the trial. All trout grew comparably while maintaining healthy bones. But the use of phosphorus improved in trout fed low-combined-withoptimal phosphorus compared with the group fed only at the higher recommended level. This suggests that a diet with low phosphorus content creates a ‘mineral hungry’ bone network. Once we provide the animal with dietary phosphorus it tends to utilise it at a faster rate as opposed to those fed the required levels continuously. Both phosphorus restriction and starvation lead to reduction in salmon growth. However, salmon is a robust animal and if starved it shows a fast compensatory growth once feeding restarts (Hvas et al. 2022). Similarly, phosphorus deficient salmon show fast compensatory bone mineralisation when phosphorus provision in their diet resumes (Witten et al. 2019, Drábiková et al. 2022). This would make salmon an interesting candidate species for alternating phosphorus feeding regimes aimed at reducing waste while maintaining performance. Another venue for sustainable phosphorus use is its recycling. Collectors below sea-cages could capture faecal waste and uneaten particles that can be then used in fertilisation of crops and support growth of farmed animals. We can find examples of a balanced nutrient reuse and redistribution of phosphorus around the planet also occurring naturally. The rivers feeding into the Pacific Ocean are lacking phosphorus and are therefore thought to be the drivers of Pacific salmon’s single spawning event before death. Pink salmon (Oncorhynchus spp.) are among so-called phosphorus transporters, with their bones containing around 10% of the element. As the salmon bring assimilated nutrients from rich marine ecosystems back to poor freshwater habitats, deposited nutrients in the form of carcasses and faeces support the local fauna and flora (Ebel et al. 2015). Acknowledgements The research that this article is based on is published in the Aquaculture journal under the title “Phosphorus requirements in sea-cage farmed Atlantic salmon with an emphasis on bone health and digestibility.” It was supported by MOWI Feed AS, Norway and it is registered as the Institute of Marine Research’s project number 15996. The study represents a collaborative effort among the Reproduction and Developmental Biology group located at Matre Research Station (IMR), MOWI Feed AS, and the Evolutionary Developmental Biology group at Ghent University. Special thanks to the team at Averøy Research Station: Jørn Age Stene, Matthew Watkins Baker, Sjur Storaas, Sindre Pettersen, Eirik Nordahl, Fredrik Røsand, Hans Henning Heyn, and Even Røisgaard for their hard and dedicated work. Many thanks to Barbara De Kegel and Karen Anita Kvestad for their technical help in the laboratory. We would also like to extend our gratitude to Aqua Kompetanse AS team: Erlend Solem, Christine Klykken, Tomas Sandnes, Susanne Tofte, and Torvald Blikra Egeland for help with the x-ray imaging. Notes Lucia Drábiková,* Saskia Kröckel, P. Eckhard Witten, Guido Riesen, Paul Morris, Agnés Ostertag, Martine Cohen-Solal, Thomas W.K. Fraser and Per Gunnar Fjelldal. * Corresponding author: Institute of Marine Research, P.O Box 1870 Nordnes, NO-5817 Bergen, Norway. lucia.drabikova@hi.no References Aas, T.S., Åsgård, T. and T. Ytrestøyl. 2022. Utilization of feed resources in the production of Atlantic salmon (Salmo salar) in Norway: An update for 2020. Aquac. Reports 26, 101316. Albrektsen, S., Hope, B. and A. Aksnes. Phosphorus (P) deficiency due to low P availability in fishmeal produced from blue whiting (Micromesistius poutassou) in feed for under-yearling Atlantic salmon (Salmo salar) smolt. Aquaculture 296:318-328. Albrektsen, S., Lock, E.J., Bæverfjord, G., Pedersen, M., Krasnov, A., Takle, H., Veiseth-Kent, E., Ørnsrud, R., Waagbø, R., Ytteborg, E., 2018. Utilization of H2SO4-hydrolysed phosphorus from herring bone by-products in feed for Atlantic salmon (Salmo salar) 0+postsmolt. Aquac. Nutr. 24, 348–365. Chatvijitkul, S., Boyd, C.E. and D.A. Davis. 2017. Nitrogen, phosphorus, and carbon concentrations in some common aquaculture feeds. J World Aqua Soc 49, 477-483, Drábiková, L., Fjelldal, P.G., De Clercq, A., Yousaf, M.N., Morken, T., McGurk, C., Witten, P.E., 2021. Vertebral column adaptations in juvenile Atlantic salmon Salmo salar, L. as a response to dietary phosphorus. Aquaculture 541, 736776. Drábiková, L., Fjelldal, P.G., De Clercq, A., Yousaf, M.N., Morken, T., McGurk, C. and P.E. Witten. 2022. What will happen to my smolt at harvest? Individually tagged Atlantic salmon help to understand possible progression and regression of vertebral deformities. Aquaculture 559: 738430. Drábiková, L., Fjelldal, P.G., Yousaf, M.N., Morken, T., De Clercq, A., McGurk, C. and P.E. Witten. 2023. Elevated water CO2 can prevent dietary-induced osteomalacia in post-smolt Atlantic salmon (Salmo salar, L.). Biomecules 13, 663. Drábiková, L., Kröckel, S., Witten, P.E., Riesen, G., Morris, P., Ostertag, A., Cohen-Solal, M., Fraser, T.W.K. and P.G. Fjelldal. 2026. Phosphorus requirements in sea-cage farmed Atlantic (CONTINUED ON PAGE 32) We can find examples of a balanced nutrient reuse and redistribution of phosphorus around the planet also occurring naturally. The rivers feeding into the Pacific Ocean are lacking phosphorus and are therefore thought to be the drivers of Pacific salmon’s single spawning event before death. Pink salmon (Oncorhynchus spp.) are among so-called phosphorus transporters, with their bones containing around 10% of the element. As the salmon bring assimilated nutrients from rich marine ecosystems back to poor freshwater habitats, deposited nutrients in the form of carcasses and faeces support the local fauna and flora.
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