My mother used to have a 200 liter tank with some cichlids in it. The two male Convict Cichlids (brothers) fought constantly over a log cave where one had made his home. Well, finally she felt bad for the other one and bought him an even bigger cave.
Instantly he scouted out the cave and claimed it as his own. But the new cave also attracted the attention of her Jack Dempsey, and he started trying to get in it (dumb fish was too big for it). The Convict wasn't happy about this and started trying to chase him off.
Being bigger, the Jack was winning. But then the other Convict came out of his log cave, from the other side of the tank, and helped his brother fight for his new cave! Together, the brothers scared the Jack off and then the two left for there respective caves.