My gut feeling after feed training RES over the summer is that RES likely have eyes that are super sensitive to light, more so than other sunfish. I believe this is the reason they do not feed train well.
Shaded cages and feeding times at dusk and dawn, or even after dark will likely lead to a higher percentage of RES becoming feed trained. That is the hypothesis I am going to test next year.
I should mention that I have a few of my feed trained RES in in an aquarium in my basement. I started feeding them rosey red FHM last week to see how they might utilize the abundant GSH hatches in my pond. Guess what? 95% of the RRFHM that have been captured and eaten have been after the lights go out in almost pitch black conditions. During the day hardly any RRFHM vanish. Last Friday after work I added 23 small RRFHM minnows to the tank, my RES ignored them all evening when the tank lights were on. When I got up the next morning and turned the lights on there were just four left.
There is a reason RES like to hang out in deeper water during the day.
