Fighter males were more aggressive than wild type males for all measured behaviours. Differences were not just quantitative but the pattern of fight reveal was also divergent. Fighter males had an normal higher swimming exercise, acting frequent fast strikes in the course of the intruder and displaying from a distance. Wild type males were less active and exhibited competitive shows mostly in close proximity to the stimuli. Females of the fighter strain, which aren’t used for fights, were also more aggressive than wild type females. Aggressive behaviours were correlated across male and feminine fighter siblings, suggesting common genetic and physiological mechanisms to male and female aggression during this species.