They'll be ok with any animal they can't catch easily. Pretty sure mine went to town on some chromis I had a while back though. Anytime they're sleeping at night and your eel can just come right out and grab an easy snack...of course, my eel is over 2 feet long now too. Still, until 6 months ago, he was a dweller of my reef tank, and I never had any problems with him bothering any of my livestock...