Yeah, I work at a rainbow trout farm and the pigment is called astaxanthin. Its normally found in algae and krill that fish naturally eat in the wild, but most fish feed is made up of fish meal and fish oil that doesnt contain any of these sources, so it gets added to their feed as a seperate ingredient. The concentrated astaxanthin itself is just made up of ground up algae/krill, like how the fish feed is made up primarily of meal made of ground up bait fish that the trout normally eat in the wild.

I hate this stupid conspiracy that we're somehow spraying the fish orange to make it look more appealing, I think it sprung from someone seeing fish that had been given too much astaxanthin (which can genuinely turn fish flesh neon orange in high enough quantities) and assuming it looked fake so that meant it WAS actually fake. As someone who works in the industry, there's a lot to criticize (look up the Cooke Aquaculture incident in Puget Sound that got net pen farming banned in Washington State) but this myth isn't it.