USE OF HYDROGEN-PEROXIDE TO TREAT EXPERIMENTALLY-INDUCED BACTERIAL GILL DISEASE IN RAINBOW-TROUT

Bacterial gill disease, experimentally produced in rainbow trout Oncor hynchus mykiss exposed to Flavobacterium branchiophilum, was effective ly treated by using l-h static baths containing hydrogen peroxide as a n alternative to treatment with chloramine-T. The optimal concentratio n of hydrogen peroxide depended on the number of treatments, the time intervals between them. and the stage: of the disease. When administer ed 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 wi th chloramine-T or 250 mg hydrogen peroxide/L; 100 mg hydrogen peroxid e/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 p eroxide as low as 25 mg/L also had very low PCM. Although levels of gi ll-associated F. branchiophilum antigen were lowest in those groups tr eated with hydrogen peroxide at 125 and 175 mg/L, higher PCM occurred with increasing concentrations of hydrogen peroxide. Chloramine-T trea tment, however, resulted in low levels of gill-associated F. branchiop hilum antigen as well as low PCM. Treatment of healthy and F. brallchi ophilum-infected groups of fish with a single I-h exposure to 300 or 4 50 mg hydrogen peroxide/L did not cause any deaths in the week followi ng exposure.