Water flow impacts group behavior in zebrafish (Danio rerio)

Constant temporal and spatial fluctuations of the physical environment pose a great challenge for individual survival, making plastic behavioral responses an important mechanism for coping with environmental fluctuations. For aquatic animals, water flow is one of the most important factors, imposing additional physiological costs and changing their relationship with the biotic environment including conspecifics, predators, and disease agents. Here, we conducted a controlled laboratory experiment to test the influence of water flow on the behavior of zebrafish (Danio rerio), considering also the impact of obstructions. Using wild-caught zebrafish, we formed groups of 6 fish and tested their behavior in 4 treatments that varied in water flow and obstructions. We used automated tracking software to estimate shoal cohesion, aggression, and activity level. Zebrafish strongly responded to the presence of even a weak flow by forming less cohesive, more aggressive, and more active groups. The effect of flow was not exaggerated by turbulence generated from obstructions. Zebrafish were also more active and more aggressive when in a structurally complex context. These findings highlight the plasticity of zebrafish social behavior and provide insight to understand the impact of water flow on behavioral plasticity of social groups.