Can I assume if I was to stock bluegill now, they wouldn’t survive without minnows?
Bluegill will eat fatheads, especially fathead fry and juvenile fatheads.
Of course, they'll also eat bugs.
If you implement a feeding program, bluegill will take to that very quickly. That's why I mentioned that you have several months of bluegill growth you could get before winter truly kicks in here in Western PA.
I did read that a fishery wasn't your primary goal for the pond, so you may not be interested in this aspect.
