Prior-residence effect in Betta splendens.

Male Siamese fighting fish were presented with the visual image of an aggressive male conspecific for a 150-min test, with attack behaviors monitored continually. A 10-day period of residency in either the test tank or its exact replica resulted in more persistent attack than 10 min of residency. Testing in water other than that in which subjects had resided for 10 days did not produce a reduction in attack. Finally, the extent of attack behavior occurring early in testing was highly and positively correlated with subsequent attack duration; that is, at the start of an encounter, and before severe physical damage has been caused, Bettas may communicate to opponents their "intention" to engage in persistent, injurious aggression.