Water turbidity increases biotic resistance of native Neotropical piscivores to alien fish

Large tropical rivers are increasingly affected by dam construction, which generally implies alteration of flow regimes, increased water transparency, decline of native species and proliferation of invasive alien species. The potential of native Neotropical piscivores to provide biotic resistance to alien fish invaders and its interaction with water turbidity was investigated through mesocosm experiments. Three invasive and two native fish species were offered as prey to three native piscivores of the Parana river in 1000 L tanks. After 48 h, prey survival was compared among trials with and without the piscivores and in turbid (~ more preserved systems) versus clear water (~ disturbed systems by damming) treatments. Prey survival, particularly of the invasive species, was significantly lower in turbid water in the presence of predators (~ 45.9% versus ~ 53.7% in clear water). Piscivores preyed more on smaller individuals in clear water and on larger preys in turbid water. Although vulnerability to predation was prey-specific, our results support the potential of native piscivores to provide biotic resistance against alien freshwater species. Water turbidity mediated the predator–prey interactions and our results confirm the hypothesis that decreased turbidity caused by dams’ construction can affect predation efficiency of native piscivores and increase the abundance of alien fish.