I remember back in my African cichlid days one of the ways around aggression issues was to grossly overstock the tank. It worked and is probably what explains what is keeping the fish in this tank from killing each other. Of course that was back in the early 80s. We did a lot of things that would piss off people these days. Slap a UG filter in that baby and you could probably give people a stroke these days.
I will say this however. That tank is the coolest, dare I say, baitbucket I have ever seen; and trust me I have seen a lot of them and most of them with a few less fish in them.