Fish Fighting Tactics
If two closely matched fish fail to decide the issue by displays, an actual fight may develop, but this is relatively rare. Two aggressors must be very closely matched, with a great deal at stake, before they fight.
How do fish make the transition from displaying to fighting?
Sometimes the transition from displaying to fighting can be rapid and dramatic, with a sudden flurry of aggression. At other times it is much more gradual, again reflecting the reluctance of fish to risk injury needlessly.
Goatfish, for example, spar rather reservedly with their barbels. The protagonists come together face-to-face, almost like fencing partners, jabbing at each other with their extended barbels. For other species, the first stage in an actual physical contest is jaw-locking. This behavior has been documented between female clownfish and different Chromis species. Jaw-locking usually involves a kind of tug-of-war, with each opponent trying to demonstrate its strength and superiority in a kind of physical extension of a display. Royal grammas perform this mouth-wrestling tenaciously, shaking their heads while locked in their embrace and sometimes tearing or otherwise damaging each other's mouthparts.
What happens when a real fight starts?
This varies from fish to fish, but there are several common threads in all altercations. For one thing, the combatants usually tend to target the same parts of their opponents' bodies. Top targets are often the fins, which makes sense because a torn fin is likely to slow down a foe. Any vulnerable part is also fair game; fish often attack the eyes and unprotected flanks of their enemies. Surgeonfishes and tangs have been known to bring their sharp tail spines to bear, wounding their opponent's flank. A full-blown fight rarely lasts more than a few seconds -- or minutes at most. Once one fish has landed a few blows or bites the impulse to fight can rapidly leave the other and it may seek to break contact and flee.
What happens after a fight?
Once the victor has been decided the losing fish must make itself scarce, otherwise its life might be at risk. The winner will not tolerate its presence in the immediate area and will continue to attack -- no mercy is given. In the open waters of the reef, this is not often a problem, but in the confines of an aquarium, the constant harrying of the victor may prove fatal. Ultimately, this could be the fate of either of the fighters in the immediate aftermath of the battle, as open wounds may become infected -- fighting is a costly business. If both survive and there is sufficient space to shelter the loser, the protagonists are unlikely to fight again.
Fish tend to remember the identity of their conquerors and do not make the same mistake twice.
What makes certain lands offish so prone to aggression in the home aquarium?
Some species of fish, such as some angelfish, are notoriously testy in the home aquarium, but a great many fish will not tolerate the presence of conspecifics. One reason for this is the comparative shortage of space and hiding places in an aquarium. Many reef fishes in the wild defend enormous territories from members of their own species. For example, tangs may defend territories running into hundreds of square feet against conspecifics and food competitors alike. Fish are also more aggressive when defending their patch and prior residence counts for a great deal in fish contests. A newly introduced fish must cope not only with the change in habitat, but also the aggressive intentions of established tankmates. The job of the aquarist is to plan ahead in order to stock compatible fish and to ensure the availability of sufficient resources in terms of food and hiding places.