The efficacy of hydrogen peroxide in controlling saprolegniasis on eggs of walleye Stizostedion vitreum, white sucker Catostomus commersoni, and paddlefish Polyodon spathula was evaluated at four private, state, and federal production hatcheries participating in an Investigational New Animal Drug efficacy study (experiment 1; walleyes) and in a laboratory-based miniature egg jar incubation system (experiment 2; walleyes, white suckers, and paddlefish). Naturally occurring fungal infestations (saprolegniasis) were observed on eggs in both experiments. Confirmatory diagnosis of infested eggs from one hatchery in experiment 1 identified the pathogen as Saprolegnia parasitica. During experiment 1, eggs were treated daily for 15 min with either 0, 500, or 750 mg/L of hydrogen peroxide, and one trial compared a 500-mg/L hydrogen peroxide treatment with a formalin treatment at 1,667 mg/L. Saprolegniasis infestation was observed in control egg jars, whereas treatment with either formalin or hydrogen peroxide virtually eliminated the infestation. Hydrogen peroxide treatments of 500 mg/L either increased egg hatch or were as effective as physical removal of infested eggs in controlling mortality. Although treatment with formalin at 1,667 mg/L significantly increased the percent eye-up of walleye eggs compared with that of those treated with hydrogen peroxide at 500 mg/L, the difference was only 1.9-2.6%. In experiment 2, noneyed eggs were treated for 15 min every other day with 0, 283, 565, or 1,130 mg/L of hydrogen peroxide until the viable eggs hatched. Saprolegniasis infestation engulfed most control eggs, whereas infestation of treated eggs was either reduced or not visible. Hydrogen peroxide significantly increased egg hatch for all three species tested in experiment 2. Although hydrogen peroxide treatments as low as 283 mg/L significantly increased walleye and white sucker hatch, treatments between 500 and 1,000 mg/L are more likely to be effective in production egg incubation systems.