It’s interesting how bichirs in groups larger than three (typically) socialize with each other. It’s not unnatural to pile up (poly pile!) with each other. I have 9 and the most I’ve seen is 5 in a pile. They maintain a natural hierarchy, with the alpha (male or female) emitting a hormone to essentially reduce or limit the growth of the others to keep them from causing problems, there can be skirmishes but in a good group it’s rare. Be sure to remember that bichirs are cannibals when young, rapidly growing out of that phase around 6 months give or take. It’s easier to phase them out of it when there’s other well fed mature bichirs there to keep them in check, so you can have large bichirs with juveniles less than half their size. It’s a rule of thumb to keep fish that won’t fit in another’s mouth but I’ve found when well fed and socialized it’s not a problem.