In Australia, feed companies are legally required to disclose ingredient details which is why Tasmanian farmed salmon is a safe, nutritious, healthy, and sustainable food.
The feed for salmon contains poultry as a cooked, human grade by-product of chicken that is powdered and added to the feed. This is a good circular economy story, using the chicken products that might otherwise have gone to waste. Instead the chicken becomes a part of the protein requirements for fish.
That protein is used by the fish to grow their bodies, their muscles, they do not become chicken because they eat chicken, just like for humans – we don’t become a cow after eating steak.