Collective behavior in animal aggregations is highly complex and spans multiple spatial scales, across a wide range of environmental conditions. In socially active fish, aggregation into schools is a widespread adaptation that confers a variety of safety benefits. The emergent patterns exhibited by collectively behaving fish schools may be influenced by biotic (i.e. predation) or abiotic (i.e. habitat complexity, turbidity) factors in the local environment. Our knowledge of the ways and extent to which environment variability affects schooling behavior at the collective level is currently limited. In this dissertation, I investigated whether environmental factors influenced the collective behavior of fish schools. I focused on three main questions: (1) does habitat context modulate the collective state of fish schools? (2) does the simultaneous presence of habitat structure and high predation risk influence the collective state of fish schools? (3) do environmental constraints on visual sensory perception affect collective responses to predation? Using advanced field methods to observe schooling behavior in restrictive environmental contexts, question one demonstrated that habitat context, not predation, drives change in the collective state of fish schools, suggesting that the local environment plays a larger role than predation risk in structuring collective behavior. Using the same field method at an anthropogenic structure containing both habitat complexity and increased predation risk, question two shows that collective behavior is influenced by the coupling of the two conditions, in a different manner than with habitat complexity alone. Finally, using a behavioral arena that creates three dimensional virtual environments, question three showed that mechanosensory information becomes prioritized when visual perception is compromised, and that multiple sensory systems can control schooling behavior in conditions where information about the environment is unreliable. As a collective itself, the results of these questions advance our understanding of the role the environment plays on influencing collective animal behavior, and offers insights into this understanding from both a mechanistic and process based perspective
