Due to the increasing use of nanomaterials in human daily life and probable release of these substances into the environment, the present study investigated the effect of the presence of colloidal silver nanoparticles (cAgNPs) in the aquatic environment on the reproduction of rainbow trout as a model aquatic organism. Chemically produced cAgNP colloid was purchased from Pars Nano-Nasb (Iran) and contained 4000mg/l silver nanoparticles in deionised water. According to the transmission electron microscopy (TEM) results, the Count median diameter of nanoparticles in the colloid was 6.47 nm. Rainbow trout eggs and sperm were obtained by stripping the fish. For each treatment 500 eggs were completely mixed with 1µl of milt. In the control group (0 mg/l cAgNPs), water was added to activate sperm motility and leading to fertilization. To evaluate effect of AgNPs on fertilization, water containing three concentrations of cAgNPs including 0.1, 0.01 and 0.001 mg/L were added for sperm activation. Resulted eggs were incubated in a recirculation incubator system at a constant temperature of 10˚C. Survival rate from 24 hours post-fertilization to the eyed-stage (eyeing rate), survival from eyed-stage to hatching (hatching rate), and survival from hatching to the end of yolk sac absorption were monitored. The results showed that the eyeing rate of all cAgNPs exposed treatments were same as the control; while the hatching rates of all cAgNPs exposed treatments was significantly lower than the control (0>0.001>0.01>0.1 mg/l). A significant decrease was observed in the survival at the end of yolk-sac absorption only in the 0.1 mg/l cAgNPs group. Also significant and dose-dependent decrease in duration of sperm motility was observed after in vitro sperm exposure to cAgNPs (0>0.001>0.01>0.1 mg/l). According to these results, presence of 0.1 mg/l cAgNPs in the water environment can affect the fertilization and reproduction success of rainbow trout. Thus, the presence of silver nanopart
