Researchers test UVB lighting to raise vitamin D in farmed salmon, with welfare caveat.
Farmed salmon in Norway now contain less vitamin D than before, a change linked to feeds with fewer marine ingredients and lower omega-3 content, according to a report published on 23 October 2025.
In controlled trials, researchers increased vitamin D levels in smolt by installing UVB lamps above rearing tanks, with exposed fish showing 2.5 to 6 times higher vitamin D₃ after four weeks and more than five times after about ten weeks.
The work, conducted by two researchers from Molde University College together with colleagues employed by Salmon Evolution, suggests UVB exposure enables salmon to synthesize vitamin D in the skin.
Industry relevance is highlighted for both fish health and consumer nutrition, given evidence that vitamin D supports immune function and wound healing in salmon.
Researchers also note a potential drawback. Continuous lighting, already common in the freshwater phase to promote feeding and growth, may disrupt circadian rhythms and melatonin regulation, with uncertain effects on robustness and welfare.
