Sorry don't know much about them. I saw a couple in a pet store a few weeks ago and left them there cause I don't have room right now. Looked cool though.
the damn thing has a hinge for a mouth and will reportedly try and swallow fish bigger then them, tru monster eater so get something fast and big that will not get close and see what happens!!
Definately don't try to keep them with any torpedo shaped fish...ie..pike cichlids, gar, polypterus, africans (unless you want to use them as feeders). Your best bet will be fish that are LARGE, and DEEP bodied...Uaru, Hoplarchus psittacus, Severums, Cichla...stuff like that. Considering how much they cost though, I wouldn't personally want to risk them gettin injured by any other tankmates...as they don't really seem like 'agile' swimmers. Just my thoughts.
Mine is in a 3' aquaria on his own. As PP says I wouldnt risk him with any fish larger than him incase they bullied and damaged him. he has bogwood in the tank so i use it as a growing on tank for my ancistrus fry as loads of algae and bogwood; ideal!