Aggressive behaviour is a complex behavioural phenotype influenced by the dynamic interaction of genetic, environmental, and epigenetic factors. Genetic studies identified key genes, including SHANK3, MAOA, SLC6A4, and genes encoding oxytocin and arginine-vasopressin receptors, involved in neurotransmitter systems processes. Variations in these genes can lead to behavioural disturbances. Environmental factors influence the complexity of gene–environment interactions in the regulation of aggressive behaviour. The epigenetic research has revealed diverse factors and mechanisms that can alter gene expression patterns associated with aggressive behaviour. The zebrafish (Danio rerio) is increasingly being used as a model organism for studying these mechanisms, due to their high genetic homology with humans and suitability for complex behavioural assays. The aim of this narrative review is to integrate, synthesise and enhance the understanding of the interplay between genetic, epigenetic, and environmental regulation of aggressive behaviour, while highlighting how zebrafish models offer valuable insights into the molecular and neural basis of aggression, with potential translational relevance to neurobehavioural disorders.