Individuals in social hierarchies engage in agonistic encounters through aggressive behaviour, driving experience-dependent shifts in social status. Historically, aggression has been linked to males and androgens, while the role of estrogens remains understudied. Cichlid fish are ideal models for investigating neuroendocrine regulation and neural basis of agonistic behaviour due to their complex hierarchies and well-defined aggressive displays. The Neotropical cichlid Cichlasoma dimerus is particularly promising species to study the neuroendocrine modulation of female aggression, as both sexes show high levels of aggressive displays. The aim of the present work is to explore how estradiol may regulate aggressive behaviour using a pharmacological approach. Fish were isolated for 15 days before receiving either an intraperitoneal injection of the aromatase inhibitor fadrozole (10 ug/g) or the vehicle. After 45 minutes they were exposed to a neutral arena with a mirror on one lateral side. Behaviour was recorded for one hour, after which animals were euthanized for sex determination and brain sampling. Butting and mouth fighting were quantified and compared between groups. Behaviour was also tracked using Any-Maze, to analyse distance moved and swimming velocity. This work provides the first evidence on the role of estradiol in aggression in female cichlid fish, and lays the groundwork for future studies on estrogenic modulation and brain aromatase activity in female aggression.