Laboratory investigations on the efficacy of hydrogen peroxide against the salmon louse Lepeophtheirus salmonis and its lexicological and histopathological effects on Atlantic salmon Salmo salar and Chinook salmon Oncorhynchus tshawytscha

The efficacy of hydrogen peroxide agalnst the common salmon louse Lepeophthejrus salmonis, and ~t s toxicity to Atlantic (Salmo salar) and chinook (Oncorhynchus tsharuytscha) salmon, were investigated under laboratory cond~tions. Twenty mlnute bath treatments of 1.5 g 1.' hydrogen peroxide at 11 "C effectively dislodged approximately 80 "Aj of the preadult and adult stages of L. salmonis, but had no significant effect on the Intensity of infection with the attached chalimus stages. More than 96 % of the chalimus larvae and 84 % of the preadults and adults recovered after a 20 min hydrogen peroxide treatment at concentrations of 1.0 to 2.0 g I-' at 11 'C. Atlantic salmon were less sensitive to hydrogen peroxide than chinook salmon. The toxicity to both salmon specles increased wlth increasing water temperatures, concentrat~on, and exposure time. Histological sections of gills revealed extensive epithelia1 liftlng and necrosis in those chinook and Atlantic salmon that exper~enced acute t o x ~c ~t y . KEY M'ORDS Hydrogen peroxide .