jd's are great, but imo they are one of those fish either best kept alone, or with a much larger fish, its like they need a supervisor to keep them in check. in my 55 i had 3, 2 paired off and beat the crap out of the other one, so i put it in the 8 footer, then the 2 i had, the male beat the crap out of the female, so i put her in the 8 footer, and now its just the male and bichir and catfish and pleco in there, the jd was trying to boss around everything except the bichir which wouldnt have any of that, till i put in my big female convict, and shes THE BOSS. and now the jd is a nice tankmate now that its been dethroned lol. have to see how that turns out tho when the jd outgrows the now much larger convict. i have no doubt it will end up in the 8 foot tank before 2 long. its intresting to note how they vary color wise depending on if they are dominant or submissive. they pickup some beautiful color if they are the ones in charge. if not they are just kinda pale green. i mean the metallic spots are there, but the base color is very pale and without luster otherwise. when they are the boss my male pick up a nice tiger striping on the base color there, its pretty. IMO, jack dempsey's are not a beginner's fish. if you dont know how to manage their aggression you could quickly run into problems with dead or battered tankmates. if you have fish smaller than the jd, its dead. my jd kills my rosy red feeders i put in for the bichir all the time, they are too big to fit in its mouth, but that doesnt stop it from ripping their eyes out and tearing heads apart, its pretty gruesome really. pretty soon it will just be able to swallow them and there wont be nothing left of the evidence.
i like that fish 
