Collective gradient sensing in fish schools

Throughout the animal kingdom, animals frequently benefit from living in groups. Models of collective behavior show that group morphologies (swarms, flocks and mills) found in nature can be generated via local social interactions. However, individuals also interact with the complex noisy environment in which they live. In this work, we experimentally investigate the performance in navigating a noisy light gradient of two unrelated freshwater species, golden shiners (Notemigonus crysoleucas) and rummy nose tetra (Hemigrammus bleheri). We find that tetras outperform shiners due to their innate individual ability to sense the environmental gradient. Using numerical simulations, we examine how group performance depends on the relative weight of social and environmental information. Our results highlight the importance of individuals using a balanced weight of social and environmental information which promotes an optimal group morphology and performance.