Use of Hydrogen Peroxide to Treat Experimentally Induced Bacterial Gill Disease in Rainbow Trout

Bacterial gill disease, experimentally produced in rainbow trout Oncorhynchus mykiss exposed to Flavobacterium branchiophilum, was effectively treated by using l-h static baths containing hydrogen peroxide as an alternative to treatment with chloramine-T. The optimal concentration of hydrogen peroxide depended on the number of treatments, the time intervals between them. and the stage: of the disease. When administered as two treatments at 48-h intervals, 250 mg hydrogen peroxide/L was more effective than 10 mg chloramine-Tn. The effectiveness of 100 mg hydrogen peroxide/L was more variable, but treatment consistently and significantly reduced percent cumulative mortality (PCM) compared with untreated control groups; treatment with 25 mg/L was less effective; Clearance of gill-associated F. branchiophilum antigen was greatest with chloramine-T or 250 mg hydrogen peroxide/L; 100 mg hydrogen peroxide/L was again more variable. Three I-h static baths at 24-h intervals reduced the concentration of hydrogen peroxide required for effective treatment, Whereas replicate groups treated with chloramine-T at 10 mg/L had the lowest PCM, those treated with concentrations of hydrogen peroxide as low as 25 mg/L also had very low PCM. Although levels of gill-associated F. branchiophilum antigen were lowest in those groups treated with hydrogen peroxide at 125 and 175 mg/L, higher PCM occurred with increasing concentrations of hydrogen peroxide. Chloramine-T treatment, however, resulted in low levels of gill-associated F. branchiophilum antigen as well as low PCM. Treatment of healthy and F. brallchiophilum-infected groups of fish with a single I-h exposure to 300 or 450 mg hydrogen peroxide/L did not cause any deaths in the week following exposure.