The ones I have keept started to get ultra aggressive once they hit 12++, my larger Dovi slowly took over a whole tank (at 3"-12" didnt bother anyone), & keept everything else in the tank in a corner (had to give him away). The male Umbes seems to be so aggressive towards a female where as he will kill her if she cant find a hiding place that he cant get into, where my Dovi paired off and stayed together. Never showing hostility towards each other.