Jeff,

I have literature that says trout are not good minnow eaters. That said, if you had brown trout they would annhilate you minnows as they are more piscivourous. It depends on the species amd strain and size also makes a difference. I also have literature that shows trout not feeding exclusively on minnows until they reach about 16 or 17 inches.

Lots of exceptions of exceptions to the rule though.

It is possible your fatheads get digested so fast they are not as visible vs. the more difficult to digest things like snails and insects?

Are your fatheads accessible to the trout? Is it possible your fathead stay primarily in your rip rap and/or vegetation and do not go as deep as your trout?

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.