Oomycete infections caused by Saprolegnia species represent an escalating problem in sustainable aquaculture development. This could be attributed to the ban of Malachite green and other carcinogenic agents aims at killing the pathogen. The increase in the incidence of saprolegniosis could also be attributed to its ability to form biofilms. In this study, the authors have investigated the effects of propionic acid (PPA) on reducing the viability of induced Saprolegnia biofilms using colorimetric MTS assay based on the reduction of tetrazolium salts.