Originally Posted by random user
" ... A fly that looks like a grain pellet ? !!!"
aka Pellet Fly. More effective if you can find out what the hatchery was feeding, exact what. Dub up a pellet that mimics the stuff; watch the floating or sinking qualities and store the 'flies' in a baby food jar of the stuff. Not the most ethical of things, but very effective (and boring in 15 minutes)..
Speaking as someone who worked in a trout hatchery and also ran it's adjoining pay-to-fish ponds, I've had plenty of time to study this and can tell you there is no truth to it.
Pellet flies are no more effective in catching hatchery trout than any other fly that you care to throw.
What the hatctery fish are conditioned to respond to is the sound of many trout chow pellets hitting the water at once. Not the sight of one single one.