Modulation of aggressive behaviour by fighting experience: mechanisms and contest outcomes.
Dyadic encounters between paradise fish (Macropodus opercularis L.) males were staged. In a first experiment, the duration of the dominance-submissive phase (cohabitation following the end of fighting) and the inter-encounter interval were manipulated. Measuring the duration both of threatening, fighting, mouthlock and head-tail display it was found that the memory of an aggressive encounter largely disappeared after 6 days and the duration of the dominance-submissive experience had no effect on the stability of memory formation in this species. In a second experiment, one group of fighting fish were separated just after the end of the fight, while concomitantly fish still fighting were also separated. On the next day, the aggressive behaviour of these two groups was compared and found that fighting decreased only in the group, of which the members had been able to finish the encounter. Our results show that: (1) post-contest harassment of the submissive has little if any impact on the behaviour changes that result; (2) an aggressive encounter affects the duration and patterns of a subsequent fight only if the fight is completed (i.e. dominance relationship develop); and (3) regardless, of the previous experience memory will fade after 6 days. In conclusion, the experience of winning or losing is the promoter of behavioural changes that result from aggressive experience. It is suggested that the social behaviour of the paradise fish determines the constraints of memory and learning in aggressive situations.