i have 1 jag, 1 dovii, 1 orange pike, and 1 jack dempsy all in a tank together all are fairly good sized (6+ to 12"),but not yet full grown. and i have not really had much aggression in any of them i only had to remove 1 texas it was getting beat up bad by all of them. but after removing that one the tank is pretty calm now cept the normal protecting their own lil space and i guess you could call it a pecking order being from top to bottom #1 jag #2 pike #3 dovii #4 jack dempsy but again that is also biggest to smallest fish in the tank. right now they are at the point of out growing their tank so maybe that is why they are peacefull, i would have thought it would have caused more aggression.