Studies on the use of hydrogen peroxide as a method for the control of sea lice on Atlantic salmon

Atlantic salmon (Salmo salar) post-smolts exposed to 1.23 hydrogen peroxide for 20 min at 13.5 C suffered an acute toxicity resulting in a 35% mortality within 2 h. Under similar conditions at 10 C no mortalities were observed with Atlantic salmon or goldsinny wrasse (Ctenolabrus rupestris). No histological changes were noted in tissues from exposed fish. Thirty-three per cent of adult and pre-adult sea lice (Lepeophtheirus salmonis) were immobilized or killed following exposure to 0.5 hydrogen peroxide at 10 C, rising to 98% at 2. Some lice were able to recover and regained normal swimming movements. Gas bubbles within the haemolymph caused affected lice to float on the water surface. A delay in the toxicity of hydrogen peroxide to copepodites occurred, with a 10% mortality following a 20 min exposure to 1.25 at 10 C rising to 100% mortality at 19 h post treatment.Dilute hydrogen peroxide was stable over the 20 min treatment period. Aeration and higher temperatures increased the long-term breakdown of a working concentration of hydrogen peroxide in seawater.