LABORATORY INVESTIGATIONS ON THE EFFICACY OF HYDROGEN-PEROXIDE AGAINST THE SALMON LOUSE LEPEOPHTHEIRUS-SALMONIS AND ITS TOXICOLOGICAL AND HISTOPATHOLOGICAL EFFECTS ON ATLANTIC SALMON SALMO-SALAR AND CHINOOK SALMON ONCORHYNCHUS-TSHAWYTSCHA

The efficacy of hydrogen peroxide against the common salmon louse Lepeophtheirus salmonis, and its toxicity to Atlantic (Salmo salar) and chinook (Oncorhynchus tshawytscha) salmon, were investigated under laboratory conditions. Twenty minute bath treatments of 1.5 g l(-1) hydrogen peroxide at 11 degrees C effectively dislodged approximately 80 % 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 l(-1) at 11 degrees C. Atlantic salmon were less sensitive to hydrogen peroxide than chinook salmon. The toxicity to both salmon species increased with increasing water temperatures, concentration, and exposure time. Histological sections of gills revealed extensive epithelial lifting and necrosis in those chinook and Atlantic salmon that experienced acute toxicity.