Aquatic fungi (Saprolegniales) are ubiquitous in natural water supplies of fish hatcheries, often causing serious disease outbreaks. The therapeutic indices as safety indicators were determined and compared for three antifungal agents, formalin (FOR), malachite green (MG), and potassium permanganate (PP), using Asipenser persicus eggs. Formalin, malachite green and potassium permanganate were evaluated in three trials approximately 30 hours after fertilization, using six concentrations: formalin lowest 400, highest 12800; malachite green lowest 0.2, highest 6.4; potassium permanganate lowest 20, highest 640 ppm. Intermediate concentrations were set by always doubling the previous concentration step. Each trial was performed in one of the eighteen 1.8 L aquaria with three replicates per treatment. Therefore, the total numbers of treatments with three controls were 57. All trials used eggs that were derived from the same egg mass with a fertilization rate of 77%. 100 eggs were randomly assigned to each aquaria in order to treat eggs for 30 minutes. Thereafter eggs were transferred to separated incubators and kept for 96 hours at a temperature of 16.6 ± 0.4°C. During 96 hours, infected, hatched and non-hatched eggs were enumerated. The differences between dead eggs in control and treated groups were used to determine lethal concentrations, and the differences between infected eggs in control and treated groups were used to establish therapeutic concentrations. Median lethal dose (LC50) and median effective dose (EC50) were determined, employing a pharmacological calculation programme. The therapeutic indices (ratio of the LC50 to the EC50) for potassium permanganate, malachite green and formalin were 5.37, 2.25, and 0.99, respectively. Therefore, potassium permanganate was shown to be safer than malachite green and formalin at given comparative concentrations to control saprolegnia infectious in A. persicus egg incubation.