I breed guppies too, but mainly because I use the fry to feed baby/newborn garters... How would you feed the fry to a pac with them being so small? I'd say you probably wouldn't have to worry about parasites if you're keeping them well, but it's not a 100% guarantee. Honestly, seems like more trouble than it's worth.

As far as feeding fish in general, I feed my pac silversides from time to time and she loves them.