Assessing the Effects of Increasing Hydrogen Peroxide Dosage on Rainbow Trout Gills Utilizing a Digitized Scoring Methodology

There is great interest in the potential use of hydrogen peroxide as a treatment for external diseases of fish, particularly bacterial gill disease. One important consideration in the evaluation of hydrogen peroxide as a disease treatment is target animal safety. The goal of this study was to document the pathological lesions of rainbow trout Oncorhynchus mykiss associated with hydrogen peroxide exposure. A digitized scoring method was developed to quantify the lesions on the target organ (i.e., gills). The index was a good indicator of the toxicity of hydrogen peroxide to juvenile rainbow trout and of the severity of the gill lesions. Increasing values of the index were observed with increasing doses of hydrogen peroxide. Most importantly, the index documented that fish surviving treatment with hydrogen peroxide recovered from the gill lesions it inflicted.