Keep it with similar sized fish that can hold their own. In my experience, their temperaments really depend on the fish around them. If they grow large and are unchallenged by others, they are the kings (and bullies) of the tank. If the sunny is nipped at, chased or harrassed by others right off the bat, they will find a cave to claim as their territory and are relatively well behaved, but they will defend that new hide. Ive had a 5" sunny put my 7" largemouth and 12" pickerel in their place, but I have also had a 2" sunny live quite well with 4" bass and a 9" pickerel, though he fought often with the other sunnys in the tank for dominance over various caves.