Like I said before, they are semi predators. Some fish like pike are complete predators that feed only on fish, frogs etc. Ide eats small minnows but it loves other food too - different bugs, snails, worms, grasshoppers and similar creatures.
It's mouth isn't
designed for predatory behavior and that means it can't eat large fish.
EDIT:
By the way, you can look at it in this video:
http://www.nomad.lv/?p=3468 [at 23:30]