Salmon skin problem rises
Aquaculture reports show a worrying rise in melanosis — darkening of Atlantic salmon flesh — linked to oxidative stress and inflammation, with one Chilean study finding up to 22% of fillets affected on some farms (x.com). Norwegian researchers point to lipid‑metabolism issues and hypoxia in sea cages as likely drivers, which matters because flesh quality directly affects harvest value and animal welfare (x.com).
Atlantic salmon can look perfectly normal on the outside and still develop black patches deep in the fillet, the part people buy as a pink slice at the store. Farmers call those patches melanosis, and processors often have to trim them out by hand or downgrade the whole fillet. (sciencedirect.com) Those dark patches are not dirt, bruises, or a cutting mistake at the factory. A 2023 chemistry study found they contain eumelanin, the same dark pigment family that colors human hair and skin. (mdpi.com) The basic chain starts with injury inside the muscle. Norwegian researchers describe an earlier stage called red focal changes, where tissue first turns red and damaged before some lesions later become black and chronic. (onlinelibrary.wiley.com) Think of oxidative stress as rust forming inside living tissue. The Chilean team behind a 2026 molecular study found signals of reactive oxygen damage, inflammation, and programmed cell death in affected salmon muscle. (sciencedirect.com) Inflammation is the fish’s repair response, like sending a cleanup crew to a burst pipe. In melanosis, that cleanup response appears to linger, and the Chilean researchers linked molecules including tumor necrosis factor alpha to the damage pathway that ends in visible dark spots. (panoramaacuicola.com) Oxygen is part of the story because salmon in sea cages do not all get the same water flow. A 2025 Norwegian paper on cage conditions warned that low oxygen episodes can develop when water exchange is weak, and hypoxia can hurt welfare and production performance. (nature.com) Hypoxia just means too little oxygen, like trying to run up stairs while breathing through a straw. Norwegian scientists reported melanosis even in salmon raised in submersible cages with minimal handling, which pushed them toward internal causes such as hypoxia and disrupted fat use rather than simple rough treatment. (salmonbusiness.com) That fat-use problem is called lipid metabolism, which is the way cells store and burn fuel. The Norwegian group said trouble in that system may help explain why damaged muscle and nearby fat cells break down in a way that sets up these lesions. (fishfarmingexpert.com) Chile’s new work suggests this is no small edge case. Industry coverage of the study says some Chilean farms have seen melanosis in as many as 22% of fillets, a high enough rate to turn a biology problem into a pricing problem. (diarioacuicola.cl) Once a processor has to cut away spotted sections, the fish is worth less even if the rest of the fillet is usable. Seafood industry reporting says severe cases can mean extra labor, downgraded product, or full discard when pigmentation is diffuse. (globalseafood.org) The shift in the research is that scientists are treating melanosis less like a cosmetic defect and more like a sign that the fish struggled before harvest. That points farmers toward oxygen control, cage conditions, and feed and metabolism studies instead of blaming the processing line after the fact. (sciencedirect.com)
