You won't see a lot of small fish activity including minnows until the water gets around 55-60 degF. They get fairly active at 50 deg but not to where you will see them a lot. I think you see them more in shallow water when the adult fish start feeding heavily and 'push'/drive the small fish out of the depths into the shallows.
Keep any 'eye' on the temps and see how close I come in my estimates.
