The intensity of aggression and fighting is much easier to understand if we examine why fish fight rather than just ascribing fighting as a characteristic of a particular species. If we understand fighting, then we can attempt to control it, and our fish will benefit. Fighting is dangerous. The loser may forfeit scales, fins, or eyes. All too often, in the confines of a small aquarium, the loser may be killed.
Fighting is also dangerous for the winner.
A lucky strike to the eye by a small opponent could debilitate even the largest fish. If possible, potential combatants should attempt to evaluate the likely consequences of a fight before the fight begins. If one of the fish stands no hope for victory, it should not enter the fight. We would expect therefore that fish would be astute to gather any pieces of information that might assist them in predicting the outcome. The issue of animal contests and information transfer before and during them is an active area in animal behavior research.