Nofima study links stress to paler salmon fillets despite increased feed pigmentation.
A new study by Norwegian food research institute Nofima has found that stress reduces the pigmentation of salmon fillets, even though more astaxanthin is being used in feed than before.
The findings suggest that environmental stressors, such as lice treatments, impact the fish’s ability to retain the pink coloration that is critical for product quality and consumer appeal.
“The needs for vitamins and antioxidants can change when salmon are exposed to stress, but we still know too little about how the environment affects fillet colour,” said Trine Ytrestøyl, senior researcher at Nofima.
The study investigated how stress from common aquaculture practices—specifically lice treatments where fish are crowded and oxygen levels drop—affects pigmentation. Analysis of commercial farming data showed that salmon subjected to frequent lice treatments had noticeably paler fillets.
Astaxanthin, a marine-derived antioxidant and pigment, is the primary source of the salmon’s pink colour. However, its uptake and retention are influenced by diet composition and environmental factors. Replacing marine ingredients with plant-based raw materials in salmon feed has reduced levels of beneficial omega-3 fatty acids and vitamin A, both of which are linked to pigmentation and fish health.
In the trial, salmon were fed diets with varying levels of vitamin A and astaxanthin, mirroring the range found in commercial feeds. Fish were then exposed to repeated stress over five weeks. Results showed that stressed salmon had less astaxanthin in their fillets compared to control groups.
However, one notable exception was observed: salmon fed diets high in both vitamin A and astaxanthin maintained fillet colour despite stress exposure. This suggests that the interaction between dietary antioxidants and stress responses is complex and context-dependent.
“Stress should be reduced as much as possible, but it cannot be eliminated entirely in farming. To ensure fish health and quality, the amount of vitamins and antioxidants in feed must be adjusted to the environmental challenges the fish face,” Ytrestøyl said.
The findings stem from the research project “Dietary factors and physiological mechanisms interact and govern pigmentation of salmon muscle,” funded by the Norwegian Seafood Research Fund (FHF).