Yeah, you can't underestimate the maw of a Crenicichla. If you are in doubt, don't keep it together. Generally though, you want the fish to be AT least half the size of the pike, its better if they are close to or large than the pike though. Depth of the fish is also very important. Don't keep shallow bodied fish like bala sharks for dithers. Keep silver dollars and the like, as they are too 'deep' bodied to be swallow, well, by most pikes...lol. Can't forget about that elastic stomach either. Almost every pike has one, and eyes that are too big for it....so its a bad combo...lol