A modeling approach to predict population-level impact of silver (Ag) to rainbow trout (<i>Oncorhynchus mykiss</i>)

Metal bioavailability plays a pivotal role in determining the toxicity of silver (Ag) to freshwater fish, such as rainbow trout (Oncorhynchus mykiss). The current study builds on an existing sodium balance model, a physiological extension of biotic ligand models (BLM). This model mechanistically describes the impact of Ag on Na ionoregulation in rainbow trout and predicts lethal effects under various Ag bioavailability conditions. However, broader implications of Ag toxicity on fish populations and its differential effects across life stages remain underexplored. First, the original extended BLM was improved to account for realistic variability in observed lethal responses of rainbow trout exposed to Ag. Next, a data-driven approach, based on relative survival fractions, was used to account for early life stage (ELS) toxicity. Finally, the physiologically extended BLM approach was integrated into an individual-based model framework to predict environmentally realistic effects of Ag on trout populations (abundance/biomass). Predictions indicate that ELS mainly influence trout population effects (decreased abundance/biomass) when exposed to silver, while effects on adults or juveniles are less critical for population persistence. Juveniles and adults are affected by higher Ag concentrations than embryos and larvae, suggesting greater sensitivity of ELS. Therefore, future development of BLMs for fish should prioritize early life stages to improve understanding of Ag toxicity and its impact on fish populations. This aligns with the goal of reducing animal testing. The presented framework addresses knowledge gaps in ecological risk assessment of Ag on freshwater fish, integrating various modeling approaches-including a physiologically extended BLM-to predict Ag effects on rainbow trout populations.