I've never tried to use a feed ring, so no input there.

I have observed that heavily feed trained adult Bluegill actually came off of feed when transplanted into a new body of water that was polluted with fathead minnows of all sizes. I had moved (85) of these Bluegill over, and they were almost off of feed 100% to the point where you didn't see the fish anymore, and we thought we had a total fish kill. They were in there though.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."