Bystanders to contests between conspecifics are primed for increased aggression in male fighting fish

Abstract

We performed two experiments in which we allowed a male fighting fish, Betta splendens, designated a bystander, to observe aggressive contests between pairs of male conspecifics. Another male (naı̈ve male) observed an empty tank or two nonaggressive males, depending on the experiment. Immediately after these observation periods, we allowed the bystander and naı̈ve male to interact in a neutral area. In both experiments, bystander males were dominant over naı̈ve males in a significant number of the encounters. Bystander males performed significantly more aggressive behaviours (displays, chases and bites) than did naı̈ve males. Differences in dominance were not due to chance differences in body size. These findings demonstrate that exposure to aggression between conspecifics increases aggressive motivation in bystander male fighting fish. We discuss briefly the implications of such social experience on the formation of dominance hierarchies. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.