<p>Complex group behavior can emerge from simple inter-individual interactions, yet how prior social experience shapes these interactions remains unclear. Using naturalistic and virtual-reality experiments, we varied prior social experience by exposing zebrafish larvae to high or low group densities, then measured its effects on future social interactions and group structure. We find that inter-individual distances decrease after exposure to high population densities and increase after exposure to low densities. These adaptations develop gradually over tens of minutes and remain stable for hours. Mechanistically, larvae estimate group density from the frequency of neighbor-evoked retinal looming events and couple interaction strength to that estimate. A time-varying computational model incorporating previous visual-social experiences accurately describes our observations. Our findings show that inter-individual interactions are not static, but continuously evolve with social experience and environmental demands, establishing larval zebrafish as a model for studying the neurobiological mechanisms of experience-dependent modulation of collective behavior.</p>