What if fighting fish cheated?

Anyone soured by human news can take comfort in the clashes of Siamese fighting fish. Among these creatures, a fighter who cheats tends to lose.

The ritualized battles might seem the perfect place for fish to bluff, posturing like supertough fighters, says Janet R.P. Halperin of the University of Toronto. However, such bluffs often backfire, she and colleagues report in the January Animal Behaviour.

Their thrash-by-thrash analyses of fish fights support a theory of animal communication proposed in the 1970s by Amotz Zahavi of Tel Aviv University. The handicap theory predicts that cheaters must suffer some disadvantage in order for a stable system of ritualized communication to evolve.

To test the idea, Halperin, David W. Dunham, and their colleagues provoked Siamese fighting fish into unusually aggressive states. The researchers isolated individual fish for weeks, then primed them for the fight by dangling fish models or mirrors in front of them for 5-minute sessions over several days.

When a live opponent appeared, the overexcited fish surged into combat, showing aggression far out of proportion to their size and strength. In essence, they bluffed.

Their rivals did not respond in the usual way. In a normal fish fight, says Halperin, combatants match each other's intensity, from showy but stately displays to tail whooshing and ritualized, fin-fraying bites. However, opponents of hyperaggressive fish held back, reminding Halperin of boxers who let attackers exhaust themselves.

Then, after 10 or 15 minutes of restrained behavior, the normal fish started fighting more fiercely. Researchers had matched the combatants for size and strength, but in 11 out of 13 battles, the honest opponent beat the bluffer.