Social Status and Investigatory Behaviour in the Angelfish (Pterophyllum Scalare)

The response of juvenile angelfish (Pterophyllum scalare) with different dominance ranks towards a potential predator and a nonthreatening novel stimulus was studied when in a group, to assess the influence of the social status on investigatory behaviour. Dominant fish showed a cautious predator inspection behaviour, often approaching the predator model from a relatively safe distance. In contrast, middle ranking fish inspected the predator model closely and the number and duration of the inspection visits to the area closest to the predator were greater than those of the other group members. Subordinate fish tended to avoid the potential predator, but showed the greatest interest in the novel harmless stimulus, investigating it more readily and for more time from the shortest distance than their companions. Dominant fish displayed a rather weak response towards the nonthreatening stimulus, exhibiting the shortest duration of investigation and the longest latency of approach. The response of intermediate ranking fish was more variable, existing little differences with that showed by any of the other fish categories in the parameters considered. The results indicate that dominance relationships within a group may affect behavioural decisions during investigatory behaviour, and suggest that individuals with different social status use different behavioural strategies dependent on the focal stimulus, possibly reflecting adaptive changes and physiological condition.