nanosilver (nag) is an antibacterial and antimicrobial agent. its wide use in hundreds of commercial products and industrial applications suggests a high potential for release into the environment. previous research indicates that nag induces different physiological responses in aquatic organisms, with different toxicological thresholds than ionic silver, indicating that nag may require a separate regulatory framework for policy on environmental release. as part of a collaborative nag addition study (environmental concentrations = 1-15μg/l), conducted at the iisd-experimental lakes area, i evaluated changes in yellow perch (perca flavescens) bioenergetics at the individual-level, and extrapolated modelled rates to the population-level for comparison before, during, and after whole-lake nag addition. condition and abundance of predatory northern pike (esox lucius) were also examined. results were compared to a nearby unmanipulated reference lake monitored over the same period. perch consumption and total metabolism decreased during and after nag addition in the experimental lake. activity levels became increasingly variable with nag addition, but decreased on average. growth rates and conversion efficiency appeared unaffected in both lakes. abundance and condition of perch remained constant over the study. by contrast, survivability of pike increased after nag addition ceased, however, condition did not improve. gross consumption of zooplankton and benthic invertebrates by perch declined during and after nag addition. this study evaluated fish effects in relation to the rest of the ecosystem – achievable only through whole-lake experimentation. based on these results, nag appears to have had significant adverse impacts on fish during the two years of exposure.