Rotation and polarisation in the locomotion of confined zebrafish

We investigate the individual and collective locomotion of zebrafish in a confined circular shallow environment. Experimentally, we observe that as they grow from larvae to adults, individual zebrafish transition from exploratory swimming to a regime where they tend to follow the wall. When several adults are present, the collective rotation displays significant amount of polarisation: a majority of fish rotate in the same direction. Inspired by the specific intermittent gait adopted by the fish, so-called burst-and-coast dynamics, we model the assembly as purely repulsive, persistent random walkers with realistic body and gait characteristics. Our model captures the individual confinement transition observed during ontogeny. More surprisingly, and despite the absence of “à la Vicsek” alignment terms, the model also captures the collective spontaneous polarisation observed in the experiment.