Efficacy of hydrogen peroxide to control mortalities associated with bacterial gill disease infections on hatchery-reared salmonids

The efficacy of hydrogen peroxide to control mortalities associated with bacterial gill disease (BGD) was evaluated in three trials conducted at two Wisconsin Department of Natural Resources hatcheries. Microscopic examination of the fish gills before treatment revealed gill damage and the presence of bacteria indicative of BGD. In separate trials, brown trout Salmo trutta, chinook salmon Oncorhynchus tshawytscha, and rainbow trout O. mykiss were exposed to hydrogen peroxide concentrations of 0, 56, 110, or 230 mg/L for 30 or 60 min every other day. In all three trials, at least one of the hydrogen peroxide treatment regimens reduced cumulative fish mortality in comparison with the controls. Exposures of 230 mg/L for 60 min increased the risk of mortality in brown trout and chinook salmon relative to that at other treatment concentrations. Exposures of up to 230 mg/L for 30 min decreased the risk of mortality in rainbow trout. Posttreatment qualitative gill examination indicated that gills of the treated fish appeared normal, whereas the gills of control fish exhibited pale coloration, clubbing of filaments, and lamellar fusion. On the basis of the efficacy data, two static bath treatment regimens were effective in the control of BGD: hydrogen peroxide administered at concentrations of 56–110 mg/L as a 60-min exposure or hydrogen peroxide administered at concentrations of 56–230 mg/L as a 30-min exposure.