Mate guarding in an Amazonian cichlid, Pterophyllum scalare

Abstract

Aggression by Pterophyllum scalare to an opposite sexed intruder was markedly reduced when the mate was absent. Territorial defence was not vigorous just after the eggs had been released and fertilized. Fish of both sexes attacked intruders of the same sex more intensely than they attacked those of the opposite sex, but males were more aggressive than females in this context. These results suggest that their aggression toward intruders serves to maintain the pair bond.