Fungal diseases are among the most detrimental factors in egg incubation next to bacterial diseases. Saprolegniosis is the most common fungal disease in freshwater hatcheries. Fish eggs are very susceptible to fungal diseases during the late stages of their development. Recently, various inorganic antibacterial and antifungal materials containing silver have been developed and some of them are in commercial use. Silver nanoparticles (Ag NPs) and Silver zeolite (SZ) are two of them. However, we don’t have any information regarding the antibacterial and antifungal effects of silver compounds on fish disease. To fill this gap, effects of silver zeolite and colloidal silver nanoparticles on in-vitro growth of fish pathogenous species of Saprolegnia sp. was investigated. The antifungal activity of silver nanoparticle and silver zeolite was evaluated by determining the minimum inhibitory concentrations (MICs) by using two-fold serial dilutions of colloidal nanosilver and silver zeolite in GY-agar at 22ºC. The growth of Saprolegnia sp. was compared to the growth on nanosilver-free and silver zeolite-free agar controls. Results show that silver nanoparticles and silver zeolite had inhibiting effect on in-vitro growth of the tested fungi. The MIC of silver nanoparticles and silver zeolite for Saprolegnia sp. were 1800 and 600 ppm respectively; which are approximately equal to 2% silver nanoparticles coloid and 2.5 % silver zeolite powder. Although the MIC value of these silver products is high as compared to other antifungal materials which are used for direct treatment of eggs or larva, but since those products could be easily mixed to or coated on other substances for indirect treatment, it seems to be useful disinfectant agents against Saprolegnia sp. Results suggested that silver nanoparticles and silver zeolite may be good candidates for indirect use in the aquaculture industry. Based on the MIC results, it could be suggested that mixing of approximately 2% silver nanop
