Linking ecotoxicology to behavior and population dynamics in fish: exploring swimming, predation, and modeling

Understanding how sublethal contaminant effects scale up to impact fish populations remains a key challenge in ecotoxicology. In this exploratory study, we propose a conceptual approach linking behavioral impairment to population dynamics using ivermectin (IVM) exposure in freshwater migratory neotropical characiform Prochilodus lineatus. Juveniles of P. lineatus were exposed for 15 days to environmentally relevant concentrations of IVM (0.5 and 1.5 µg·L-1), and escape performance was assessed via maximum swimming speed (MSS) during a predator avoidance response. A significant reduction in MSS was detected at 0.5 µg·L-1. A logistic model was then used to estimate predator capture probability from normalized MSS, and this relationship was integrated into a virtual population analysis by adjusting natural mortality. Under this scenario, population trajectories showed an accelerated decline, particularly in early years, as compared with a no-IVM baseline. While simplified, this framework demonstrates how behavioral endpoints can be used to generate first-order approximations of demographic consequences. Rather than offering a formal risk assessment, our goal is to illustrate a transferable and hypothesis-driven method that connects individual-level toxicological effects with ecological outcomes. Given the widespread use of IVM in floodplain cattle production and the ecological relevance of P. lineatus, this case highlights the potential of sublethal contaminants to alter fish population and stocks. The framework may serve as a starting point for integrating behavioral biomarkers into population-level models in support of environmental assessment and decision making, especially in data-limited contexts.