The aggressive behaviour between territorial [formula omitted] (pisces, cichlidae) with unlimited or only visual contact

Abstract

The development of aggression between territorial fish has mainly been studied in laboratory experiments using only visual contact. In this study, comparisons of the aggressive behaviour were made between conditions of unlimited and only visual contact. Fighting between two territorial cichlids in direct contact decreased over time in a way similar to the aggressive activity between subjects permitted only visual contact. However, there were also important differences between the two conditions of contact. Low-intensity aggression with a distance between the subjects occurred frequently in free interaction but was generally not observed under conditions of visual contact. The presence of non-territorial fish increased the aggression between subjects with visual contact but conversely had no influence on fighting and decreased low-intensity aggression between freely interacting subjects. In addition, the low level of aggression after some time of unlimited contact was not transferred to a subsequent period of visual contact. The results indicate that the decrease of aggression under conditions of visual contact is caused by habituation, whereas in a free interaction a balance is also developed between attack and escape tendencies.