Aggression is important in the life history of most vertebrate species and influences ecological and social relationships by regulating the dynamics of territoriality, hierarchy, predation and resource utilization. The expression of aggressive behaviour develops as an individual ages and is often shaped by social experience. Even though the heritability of traits that yield dominant–subordinate relationships is high, strong environmental influences also shape the expression of these individual behaviours. In this study we present evidence for the first time of a necessary interplay between factors that generate behavioural phenotypic plasticity in zebrafish. Select presumptively genetic and environmental elements interacted developmentally to produce the behavioural phenotypes necessary for dominant–subordinate relationships in dyads. Aggressive and submissive acts increased in focus and intensity and were correlated with social rank during development, but decreased with duration of the paired interaction.