Background and Objectives: Nanotechnology defined as understanding and controlling of materials at dimension between 1-100 nm, which show unusual physical and chemical properties. With Increasing development of nanotechnology, concerns associated with release of materials containing nanoparticles into the environment is rising. The purpose of this study is investigation of salinity effect on the acute toxicity of silver nanoparticles in rainbow trout fry (Oncorhynchusmykiss).
Materials and Methods: In order to conduct the toxicity tests, the Caspian Seawater(12±0.2 ppt) and (0.4 ppt) as sources of brackish water and freshwater were used, respectively. Toxicity of silvernano particles were evaluated in brackish water and freshwater at concentrations of1, 2, 4, 8, 16, 32and64ppm and  0.12, 0.25, 0.5, 1, 2, 4 and8 ppm, respectively. In addition, in order to investigate the quality of the used silver nanoparticles the Zetasizer, ICP, and TEM method were applied.
Results: Results of 96-hour median lethal concentration(LC50 96h), showed that toxicity of silver nanoparticles for rain bow trout fry in brackish water is 12 times less than its toxicity in freshwater.
Conclusion: According to the toxicity categories, analysis of the results showed that, for rainbow trout fry (1g), silver nanoparticles are classified as highly toxic agent substances in fresh water, and little toxic in brackish water, respectively.