To assess how flow affects school structure and threat detection, startle response rates of solitary and small groups of giant danio Devario aequipinnatus to visual looming stimuli were compared in flow and no‐flow conditions. The instantaneous position and heading of each D. aequipinnatus was extracted from high‐speed videos. Behavioural results indicate that (1) school structure is altered in flow such that D. aequipinnatus...