A recent study reveals that Atlantic salmon can synthesize vitamin D when exposed to sunlight, challenging previous assumptions that fish rely solely on dietary sources.
A collaboration between Nordlaks, Norwegian University of Life Sciences (NMBU), University of Stavanger (UiS), FishLab, and Skretting has for the first time documented that Atlantic salmon can produce vitamin D on their own when exposed to sunlight.
This study has been published in Aquaculture Nutrition and provides new and important insights into the nutritional needs of salmon, making a significant contribution to research on fish health.
According to David Knudsen, Global Innovation Manager at Skretting, who led the study, “this is a breakthrough in understanding how salmon obtain vitamin D. Previously it was believed that fish only got vitamin D from their feed, but the results now show that salmon in the sea can produce the vitamin themselves, similar to humans and other animals.”
The results show that salmon in open sea farms have up to 20 times higher vitamin D levels than fish in closed systems. This is because salmon, like humans, can synthesize vitamin D in the skin when exposed to sunlight.
Knudsen notes that as more salmon farming moves to land‑based facilities (with no access to natural sunlight), producers need to be aware that fish may no longer be able to produce vitamin D naturally. In such cases, it may be necessary to compensate by adding vitamin D to feed or by using UV light to ensure fish health and nutritional quality for consumers.
The study shows that vitamin D levels drop significantly in the winter months and in fish raised indoors without access to sunlight. This may partly explain increases in skin wounds and infections during darker periods. Research in human nutrition suggests that adequate vitamin D may support better barrier function and quicker wound healing.
Christina Husebø, a veterinarian at Skretting, says “there is still much to learn about salmon nutritional needs and how vitamin D influences fish health and welfare. The research was conducted on salmon from 15 different Norwegian farms and clearly shows differences between fish raised at sea and in land‑based systems.”
Although the role of vitamin D for the immune system is well documented in humans and other mammals, more research is needed for fish. Skretting is continuing studies on how different levels of vitamin D affect salmon health, especially regarding skin health and wound issues.
Reference
Husebø, C. A., Berge, K., Keitel-Gröner, F., Hoel, E., Rennemo, J., Sandstad, M., Bjerkestrand, K. M., Lorentzen, L., Welde, E., Morken, T., Stubhaug, I., Mullins, J., Bjørgen, H., Bossum, T., Brede, C., & Knudsen, D. L. (2025). Field Evidence of Endogenous Vitamin D Synthesis in Atlantic Salmon Induced by Natural Sunlight. Aquaculture Nutrition, 2025(1). https://doi.org/10.1155/anu/3823472
