The Diet
Caged salmons are fed pills that are made of 20% fish and fish oil - those already bringing a lot of unwanted substances - and the rest is a mix of gluten, soy, chicken fat, genetically engineered yeast, Therefore their meat would naturally be grey.
One of the ingredient in these pellets is astaxanthin. Astaxanthin is a strong anti-oxidant which is sometimes made “naturally” through algae or pulverized crustaceans; other times they produce it in labs, using petrochemicals.