Collective behavior may be elicited or can spontaneously emerge by a combination of interactions with the physical environment and conspecifics moving within that environment. To investigate the relative contributions of these factors in a small millimeter-scale swimming organism, we observed larval zebrafish, interacting at varying densities under circular confinement. If left undisturbed, larval zebrafish swim intermittently in a burst and coast manner and are socially independent at this developmental stage, before shoaling behavioral onset. Our aim was to explore the behavior these larvae as they swim together inside circular confinements. We report here our analysis of a new observation for this well-studied species: in circular confinement and at sufficiently high densities, the larvae collectively circle rapidly alongside the boundary. This is a new physical example of self-organization of mesoscale living active matter driven by boundaries and environment geometry. We believe this is a step forward toward using a prominent biological model system in a new interdisciplinary context to advance knowledge of the physics of social interactions.

集体行为可以通过与物理环境的相互作用和在该环境中移动的同种生物的结合来引发或自发出现。为了研究这些因素在小型毫米级游泳生物中的相对贡献，我们观察了斑马鱼幼虫，它们在圆形限制下以不同的密度相互作用。如果不受干扰，幼虫斑马鱼会间歇性地以爆发和海岸方式游泳，并且在这个发育阶段在浅滩行为开始之前是社会独立的。我们的目标是探索这些幼虫在圆形限制内一起游泳时的行为。我们在此报告我们对这个经过充分研究的物种的新观察结果的分析：在圆形限制和足够高的密度下，幼虫共同沿着边界快速旋转。这是边界和环境几何驱动的中尺度生物活性物质自组织的新物理例子。我们相信这是朝着在新的跨学科背景下使用突出的生物模型系统推进社会互动物理学知识迈出的一步。