Deffinetly the barb's are huge fin nippers. Mine just killed a 3 dollar fancy guppy.
I was away for 3 hours and I came back and there was a clear skeloton with a bite in his head floating around. (Probably from the loach) I was quite sad because my guppy was gonna get his new girlfriend the same day and make me lot's of feeder guppy's. :P