Environmental enrichment reduces aggression of pearl cichlid, Geophagus brasiliensis, during resident-intruder interactions

Among fishes, when residents and intruders fight, residents usually win, most likely because they value the residence more than intruders. We hypothesized that enriched environments increase the value of an area in dispute, causing a resident to more fiercely defend a resource-rich environment than a poor one. However, in the present study, intruder-resident tests with the pearl cichlid, Geophagus brasiliensis, showed environmental enrichment actually reduces aggression and can even lead to co-habitation without fighting. Additionally, in our experiments, the prior residence effect occurred irrespective of enrichment condition. Decreased visibility from increased habitat complexity reduces interactions between fish and consequently might explain the lower aggression observed herein.