Fast body turns in a cichlid fish

Abstract

THE African cichlid fish Haplochromis burtoni, is sexually dimorphic. The female is smaller and of an homogeneous beige colour, whereas the male has bright colour patterns which he can turn on and off quickly. These are important signals, particularly during aggressive interactions¹, since these fish rely extensively, although not exclusively, on visual cues in their social behaviour². Sound production does not seem to be involved³, but chemical stimuli are important in male–female encounters during reproduction⁴. Colony observations in aquaria have shown that after the disruption of an established social situation, there is considerable behavioural interaction until the new social order is stabilised. Subsequent behavioural interaction is much less frequent, although a rank order is maintained. Since most social encounters seem to depend on visual cues, it seemed likely that vision was involved in the subtle interactions which characterise behaviour in an established social order. I have therefore monitored and analysed the horizontal eye movements of male H. burtoni during social encounters. I found a new kind of very fast body movement, during which the eyes were held fixed, which are correlated with specific types of behavioural interactions.