The aggressive behaviour between territorial Astatotilapia burtoni (pisces, cichlidae) with unlimited or only visual...

The relationship between territorial Astatotilapia burtoni was studied under conditions of both unlimited and only visual contact. The aggressive activity between territorial fish coming into visual contact remained at a high level during the seven days of observation. Territorial fish permitted unlimited contact showed, on the other hand, a marked decreased intensity of aggression during the first day of contact. Results from experiments using visual contact are therefore not necessarily relevant for a free contact situation. A detailed examination of low-intensity aggression indicated that a dynamic equilibrium between attack and escape tendencies, as regulated by distance to the territorial border, controlled aggression between freely interacting fish. Low-intensity aggression seldom occurred between fish separated by a glass partition and a similar equilibrium did not seem to develop in this situation. The difference between the findings on A. burtoni and results from similar experiments on another cichlid fish Pseudocrenilabrus multicolor could be explained by differences in the relative importance of two factors in the regulation of aggression; (1) a balance between attack and escape tendencies and (2) a decrease of the attack tendency (habituation) below a critical threshold value.