Aggression of zebrafish following pharmacological manipulations of various nodes within neurological pathways proposed to regulate aggressive behaviour. A. The hypothalamo-neurohypophysial system (HNS) pathway in males. B. The serotonin (5-HT) pathway in males. C. The HNS pathway in females. Specific agents known to agonise or antagonise particular receptors or inhibit transporters within the identified axes were administered and the effect on aggression determined (treated) compared to a sham administration (sham) with n = 6-9 fish. AVT, arginine vasotocin acetate salt; Manning, Manning compound; FL, fluoxetine HCl; WAY100,635, WAY100,635 maleate salt. Significant changes in aggression (number of aggressive acts per 5 min observation) are indicated by asterisks (*P < 0.05; **P < 0.01; ***P < 0.001).