no wild-caught minnows! wild-caught fish can have icky diseases and things all over them, not even the kind you can see either. i don't think wild fish get Ich, usually internal parasites, and how will you see them?
Live-Bearer fry and small fish are good, though, and if you have the stomach some squashed snails, sliced earthworms/nightcrawlers, and live fruitflies work well ^^