A better home makes cichlids friendlier, according to research published in the most recent issue of the journal Neotropical Ichthyology by Brazilian scientists Vivian Kadry and Rodrigo Barreto.
Using the Pearl cichlid (Geophagus brasiliensis) as a subject, the authors tested the hypothesis 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.
They did so by placing the cichlids in two sets of aquaria: a habitat-enriched environment with two pebbles and a plastic kelp model and a non-enriched environment consisting of only a bare tank.
The authors maintained a resident fish in the tanks before placing an intruder of equal size into the tank and scoring for the following forms of aggressive behaviour between the fishes: biting, lateral pushing, chasing or mouth wrestling.
The results indicated that all of the fishes in the bare tanks engaged in some form of aggression, but only half of those in the enriched tanks did so.
This phenomenon of an increased quality of the territory leading to less fighting or promoting peaceful cohabitation is hypothesised to be the result of an increased energy cost to the resident in a territory with reduced visibility.
Because of this cost increase, the authors surmise, the fish chooses to be less aggressive and peaceful cohabitation as the best strategy to adopt.
For more information, see the paper: Kadry, VO and RE Barreto (2010) Environmental enrichment reduces aggression of pearl cichlid, Geophagus brasiliensis, during resident-intruder interactions. Neotropical Ichthyology 8, pp. 329–332.