Aggression and dominance in cichlids in resident-intruder tests: the role of environmental enrichment

Abstract

When establishing dominance residents have a greater likelihood to dominate intruders than vice versa, partially because the resident has more to loose that the intruder has to win. This is known as the prior residency effect. In environmentally rich environments this effect should be stronger than in poor environments. Recently Kadry & Barreto (2010, Neotrop Ichthyol 8: 329-332) tested this in the pearl cichlid Geophagus brasiliensis (17 test pairs) and reported that environmental enrichment led to a reduction of aggression. We here present data on four other cichlids (332 test pairs) showing a stronger prior residency effect in enriched conditions, and, for two species, an increase in aggression. We discuss possible reasons for the differences between studies, focussing on the relationship between aggression and dominance and sample size effects.