Zebrafish shoals share leadership during continuous decision-making on the move in a three-room Y-maze

Collective decision-making in animal groups is often studied using short, trial-based mazes experimental setups that restrict observations to isolated choice events. However, how leadership and decision dynamics unfold over extended periods in symmetric environments remains poorly understood. Here we introduce a novel cyclic three-room Y-shaped environment that enables continuous, and autonomous sequences of collective decisions without experimental reset. We tracked the positions and identities of 20 groups of five AB-strand zebrafish (Danio rerio) during one-hour sessions in which animals freely transitioned between three identical rooms connected by visually isolated identical corridors. We show that this symmetric Y-maze enables the collection of large amounts of data to study decision-making with a few replicates, because habituation occurs after 45 minutes of exploration. After an initial exploration phase, groups reached a stable behavioural regime, generating thousands of decision events per replicate. Collective dynamics were consistent across spatial contexts, indicating that the symmetric architecture does not bias movement patterns, as opposed to traditional mazes. We show that zebrafish leadership is typically shared among shoal members, with leaders often acting as decision-makers. By transforming a classical maze into a self-renewing decision system, this approach enables the study of long-term collective dynamics and spontaneous leadership in controlled yet ecologically relevant conditions. Author summarypresentation