Behavioural and physiological responses of prey fish to an invasive predator

Local predator density should affect prey responses to predators by influencing predator recognition and/or general risk avoidance amongst prey. I investigated whether behavioural and physiological responses of juvenile striped parrotfish (Scarus iseri) to predatory invasive Indo-Pacific lionfish (Pterois sp.) varied with local native and invasive predator density. Parrotfish exhibited evasive behavioural changes in response to visual and chemical stimuli from a native predator (Epinephelus striatus) but not to lionfish stimuli. However, parrotfish from reefs with high compared to low predator densities exhibited more evasive behaviour and colouration responses overall. Parrotfish from reefs with high predator densities also had higher survival rates in encounters with lionfish. Steroid hormone reactivity did not vary across parrotfish groups. Selective predation by lionfish of risk-taking prey fish could be resulting in greater cautiousness in some prey populations. This heightened risk avoidance ultimately aids prey fish evasion of invasive lionfish in the absence of predator recognition.