Hydrogen peroxide treatment of Atlantic salmon temporarily decreases oxygen consumption but has negligible effects on hypoxia tolerance and aerobic performance

Abstract

Hydrogen peroxide is widely used as a treatment of ectoparasite (e.g. salmon lice, amoebic gill disease) affected Atlantic salmon (Salmo salar) in aquaculture but has frequently caused unacceptable levels of mortality. Hydrogen peroxide toxicity increases with dose, exposure duration and temperature, and can cause an acute stress response, oxidative stress, gill damage, respiratory acidosis and altered gas and ion exchange. The combined stress effects have the potential to cause sub-lethal impacts on aerobic capacity that affects hypoxia tolerance and swimming performance. Here, we tested the sub-lethal effects of hydrogen peroxide treatment on the aerobic capacity, hypoxia tolerance and gill histopathology of healthy Atlantic salmon. Hydrogen peroxide treatment (1250 ppm at 12 °C for 20 min) caused a significant but negligible reduction in acute hypoxia tolerance (lost equilibrium at slightly higher levels of dissolved oxygen) immediately following treatment, but not in the 14 days afterwards. Immediately following hydrogen peroxide treatment (1250 ppm at 16 °C for 20 min) oxygen consumption was reduced for up to 20 min in normoxia and 40 min in hypoxia. However, following transient reductions in oxygen consumption the maximum metabolic rate and Ucrit measured in a swim flume were unaffected by hydrogen peroxide exposure (1250 ppm at 16 °C). Resting metabolic rate was unaffected by hydrogen peroxide treatment in all experiments. Hydrogen peroxide exposure caused non-homogenous lamellar epithelium lifting with subepithelial oedema and multi-focal lamellar fusion. The reduction in oxygen consumption following hydrogen peroxide treatment was likely caused by an increase in blood oxygen due to the breakdown of hydrogen peroxide by catalase and other oxidative enzymes in the fish tissues. Ultimately, hydrogen peroxide did not affect aerobic performance and had negligible impacts on hypoxia tolerance, suggesting that hydrogen peroxide has minimal sub-lethal impacts on aerobic performance of healthy Atlantic salmon at the doses used here.