I second a bullhead. I caught one out of a lake, threw it in my koi pond, and had it trained to eat out of my hand and take pellets within a week or so. Very cool fish
gulper will eat up the bichir in no time. Wether it fits in his mouth or not. Something to consider when thinking of a bullhead also. Big ol mouths and a tankmate that looks like a worm.. If it were me, i would go synodontis. Tiny mouths, and most will live peaceful with your bichir.