The Safety and Effectiveness of Various Hydrogen Peroxide and Iodine Treatment Regimens for Rainbow Trout Egg Disinfection

Four tests were conducted to evaluate iodine and hydrogen peroxide for the disinfection of rainbow trout Oncorhynchus mykiss eggs at higher doses for shorter durations than previously studied. In the first test, eyed eggs were exposed to (1) 2,000 mg iodine/L for 10 min, (2) 100 mg iodine/L for 15 min, (3) 30 g hydrogen peroxide/L for 1 min, (4) 6 g hydrogen peroxide/L for 5 min, or (5) no treatment. Iodine (2,000 mg/L) or hydrogen peroxide (30 g/L) significantly reduced bacterial loads on eggs but did not significantly affect egg survival or fry deformity rates. Hydrogen peroxide at 30 g/L for 1 min was generally better for bacterial control than the other treatments, but the 2,000-mg/L iodine treatment also was effective. A second test assessed the effect of hydrogen peroxide on pH at various levels of water hardness. The pH of hydrogen peroxide solutions dropped as total hardness levels decreased, but buffering with at least 1.32 g NaHCO3/L returned pH to approximately neutral levels. In the third test, in which eggs were treated 30 or 60 min postfertilization, there was no significant difference in survival between those treated with 15 g of buffered hydrogen peroxide/L for 2 min and that of the controls. However, at both 30 and 60 min postfertilization, the 2,000-mg/L iodine treatment induced higher levels of egg mortality than in eggs treated with hydrogen peroxide and the controls. In the fourth test, the serial combination of both 30 g hydrogen peroxide/L and 2,000 mg iodine/L was highly lethal if hydrogen peroxide was the first of the two treatments. The survival of eggs treated in the reverse order (iodine first) did not significantly differ from that of controls. These results indicate that hydrogen peroxide was effective in safely reducing the abundance of bacteria on eggs in small-scale tests when buffered, but production-scale experiments with hydrogen peroxide are recommended before implementation of this treatment.