Anyway my opoint in asking who made the pellets and what was in them was to point out there is insufficient data to make a reasonable postulation as to why the farmed fish go for it and the wild ones don't.
Not really. It's conditioning.
If you start with juvenile fish, and feed them manufactured feeds their whole lives, that's all they know. They still respond to "normal evolutionary" cues in their prey when released into the wild. That is hard-wired genetically. But the pellet is foreign completely to wild fish.
When you bring wild fish into a hatchery for the first time, it's very difficult to get them onto pelleted feeds. It's alien to them. You usually have to feed them chopped up bits of herring or other bait fish, and slowly acclimate them to pellets. Sometimes, it doesn't work at all, and you have sickly fish that won't take a pellet. They end up moribund and eventually culled.