We have Red shiners (Cyprinella Lutrensis) in the streams and rivers in my area (south-central Kansas). I think they would be an interesting forage fish for some PB people to try for several reasons.
First, they will not get too large for your apex predators. The literature says 3-3.5" maximum length. This matches up well with my limited observations.
Second, they are actually an egg-eating species. If you have a pond with overpopulation concerns on one of your species, then there is a possibility that Red shiners could help out by eating eggs in the years that have massive spawns.