Automatic quantification of juvenile zebrafish aggression

•Novel software can automatically quantify zebrafish aggression and locomotion.•One month-old juvenile zebrafish show similar aggression levels as adult fish.•Zebrafish aggression levels are stable throughout the day and across the year.•Automatic quantification can detect alterations to aggression levels caused by drug treatment or mutation. Although aggression is a common symptom of psychiatric disorders the drugs available to treat it are non-specific and can have unwanted side effects. The zebrafish is an ideal model for aggression research. Zebrafish are small, amenable to genetic and pharmacological manipulation, and agonistic behaviour can be measured reliably. In this study we have established a novel setup to automatically quantify aggression and locomotion in one-month old juvenile zebrafish, a stage at which fish exhibit adult-like behaviour but are small so that one camera can film several animals. We have validated our novel software by comparison to manual quantification of behaviour, characterised the aggression of one-month old fish, and demonstrated that we can detect alterations to aggression caused by mutation or drug application. The ability to record up to 12 juvenile fish allows us to speed up and standardise data acquisition compared to studies of single fish. This setup appears to be suitable to screen for drugs that decrease zebrafish aggression as a first step toward developing novel treatments for this behaviour.