Reducing or Withholding Hydrogen Peroxide Treatment during a Critical Stage of Rainbow Trout Development: Effects on Eyed Eggs, Hatch, Deformities, and Fungal Control

In two separate trials, eggs of rainbow trout Oncorhynchus mykiss were cultured with the use of hydrogen peroxide and formalin treatments to control fungal infections. For the first trial, treatment regimens consisted of no chemical treatment (control) or daily treatments of either hydrogen peroxide at 500 mg/L for 35 min or formalin at 1,667 mg/L for 15 min. Hydrogen peroxide treatment duration was reduced to 5 min daily during 70–140 daily temperature units (DTU°C). In this trial, 27% of control eggs were infected with fungus, compared with 0% for the hydrogen peroxide and formalin treatments. Eyed egg percentages were significantly lower for control eggs compared with the hydrogen peroxide and formalin treatments. Comparing formalin and hydrogen peroxide treatments, percent hatch at 91% and 90% and percent deformities at 1.0% and 1.3%, respectively, were not significantly different. In the second trial, rainbow trout eggs were reared from fertilization to hatch under four treatment regiments: (1) control or no chemical treatment, (2) 500 mg hydrogen peroxide/L for 35 min daily (hydrogen peroxide A), (3) 500 mg hydrogen peroxide/L for 35 min daily with treatment completely withheld during 70–140 DTU°C (hydrogen peroxide B), and (4) 1,667 mg formalin/L for 15 min daily. Within this trial 15% of control eggs were infected with fungus, compared with 1% for hydrogen peroxide B and 0% for both hydrogen peroxide A and formalin. Eyed egg percentages were significantly better for hydrogen peroxide B than for hydrogen peroxide A. Hatch was significantly reduced in the control group compared with the formalin treatment. Incidence of deformities was not significantly altered by treatment type.