I know others have had very poor luck keeping anything else with e cats, but when I had mine I kept it with some blind cave tetras for about a month. I'm pretty sure they would've lasted longer, but my brother forgot to feed the e cat while I was away on vacation and it slowly began to pick off the tetras one by one. I'd suggest not putting in any fish you're particularly fond of, and whatever you do, make sure to keep the e cat well fed!