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Aversive conditions can elicit fear and the subsequent activation of the sympathetic nervous system induces ‘fight or flight’ responses. Previous unpleasant experiences may trigger fear-induced aggression and heightened aggression is a behavioral phenotype associated to various psychopathologies. Since the conspecific alarm substance (CAS) acts as chemical cue that elicits fear in fish species, we evaluated whether acute and chronic CAS exposures modulate aggression in wild-type (WT) and leopard (leo) zebrafish using the mirror-induced aggression (MIA) test. Because monoamines influence mood and behavior, we also assessed the effects of CAS on brain Z-MAO activity. CAS was isolated from phenotypically similar donor fish and 3.5 mL/L was used for the experiments. In the acute protocol, fish were tested following a single CAS exposure (5 min). The chronic exposure consisted of exposing the animals once daily (5 min) for 7 consecutive days, with a subsequent test on the 8th day. CAS acutely increased aggression and decreased Z-MAO activity in both populations. Conversely, chronic CAS exposure reduced aggression and inhibited locomotion without affecting Z-MAO. Differently than WT, leo showed decreased absolute turn angle and increased latency to attack the mirror following the chronic exposure. At baseline conditions, WT were more active, aggressive, and had a lower brain Z-MAO activity than leo. Overall, we suggest a distinct acute and chronic effect of CAS on aggression and a possible involvement of brain Z-MAO in aggressive behaviors. Moreover, the use of different zebrafish populations could serve as emergent tools to investigate the neurobehavioral bases of fear-induced aggression.Representative data following acute and repeated CAS exposure on aggressive behavior and brain Z-MAO activity of WT and leo zebrafish populations. The ethograms show distance traveled, aggressive episodes, and duration of aggressive behaviors measured in the MIA test.CAS modulates aggression and brain Z-MAO of WT and leo zebrafish populations.Baseline conditions reflect increased aggression and lower Z-MAO activity in WT.Acute CAS exposure exacerbates aggression and decreases Z-MAO activity of zebrafish.Chronic CAS exposure impairs locomotion without changing Z-MAO activity.Motor patterns in leo are altered following repeated CAS exposure.