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The hypothalamic-pituitary-interrenal (HPI) axis is centrally implicated in stressor mitigation in teleost fishes. Sustained HPI axis activation can be detrimental to the physiological functioning of an organism and can result in fitness-related trade-offs. Predator-induced mortality is known to be higher in stressed fish than in unstressed conspecifics, suggesting a role for the HPI axis in mediating fish behaviour. However, the underlying specific mechanism(s) for this phenomenon is(are) unknown. The purpose of the current study was to address how the HPI axis influences risk-taking, and antipredator behaviours in a wild teleost, the pumpkinseed sunfish (Lepomis gibbosus). Here, individual juvenile pumpkinseed were implanted either with cocoa butter as a sham control or with a biologically-relevant concentration of cortisol. Forty-eight hours post-implantation, fish were assessed for behavioural metrics associated with …