I've never kept one, but people seem to keep them with anything large and not very aggressive. I have seen them in a tank with atabpo pike cichlids, so maybe even some aggressive fish? IDK. It will outgrow even a 120g eventually. Why don't you make another thread about it?Oh I know. The clown knife is in a 75 gallon, upgrading to a 120 gallon once he hits 7”. Right now he’s around 5”