Little is known about indirect behavioral effects of introduced predators despite the importance of indirect predator-prey interactions for community trophic structure. It has been hypothesized that prey are unable to recognize cues of truly novel predators, which would weaken indirect effects and lead to increased prey mortality. Indeed, prey naiveté is proposed as one of the reasons behind species extinctions after introduction of predatory fish; however, the underlying mechanism has not been tested explicitly. This study examined the naiveté hypothesis and assessed direct and indirect effects of a non-native predator using peacock bass (Cichla kelberi) in Paraná River, Brazil. A very diverse system with high native predator richness, Paraná River was nevertheless vulnerable to this introduced piscivore, which caused a great reduction in richness and abundance of native fish in reservoir environments. We tested whether lack of predator recognition could be responsible for prey species extinctions, whether peacock bass had indirect effects on its prey feeding activity, and, finally, whether these predator-prey interactions were modified by aquatic vegetation.

Results/Conclusions

Our results show that prey (Hemigrammus marginatus) responded to both visual and chemical cues of C. kelberi and displayed avoidance behaviors equal to or greater than those observed with a native predator, Hoplias malabaricus. Presence of aquatic vegetation resulted in only a small decrease in prey mortality when compared to unvegetated controls. We discuss implications of these findings for mitigation of the effects of this invasive predator on native prey. This study also contributes to our limited understanding of the indirect effects of predators in the context of invasive species.