Анотация: Recently, commercial nanometer sized silver is extensively used for its antibacterial effect; however, nanoparticles may also have ecotoxicological effects after being discharged into aquatic ecosystems. Nanometer sized silver can flow into water ecosystems, where it can exert a variety of physiologically effects in aquatic animals, including fish. The current research aimed to examine the effect of nanometer sized Iranian commercial nanosilver (Nanocid) on the mortality response of two freshwater fish species - Silver Carp (Hypophthalmicthys molitrix) and Goldfish (Carassius auratus) and define the relationship between nanoparticle toxicity concentration and survival of these species