Can lowering water temperature during hydrogen peroxide treatment reduce salmon mortality?

Hydrogen peroxide was recently reintroduced as a delousing agent in Norway in 2009, and its use has increased significantly over the past six years. The industry currently uses concentrations of 1.3-1.8 g L-1 of hydrogen peroxide in salmon delousing. A recent publication revealed hydrogen peroxide treatment during summer in Norway resulted in extremely high fish mortalities, with over 140,000 salmon killed at two Marine Harvest farms due to hydrogen peroxide treatment. The cause of such high mortality was most likely due to water temperatures above the recommended maximum of 13C during treatment. A solution to decrease salmon mortality during hydrogen peroxide treatment could be using lower water temperatures during treatment. However, the jump from warmer temperatures to colder temperatures could potentially cause increased stress and temperature shock to the salmon, which could influence mortality during and after treatment. Therefore, it is important to test if temperature shock and hydrogen peroxide treatment together can influence salmon mortality. The aim of our experiment is to determine how the combination of temperature shock and hydrogen peroxide treatment influences the mortality of salmon and pre-adult lice removal efficiency.

Expected distress for the animals will be the same as under commercial bath treatments with hydrogen peroxide of which is considered moderate, but can be lethal. There will be eight treatment groups: each treatment will have a pre-treatment and post-treatment temperature water temperature of either 10, 13 and 16C, and a treatment temperature of either 7, 10 or 13C. The experimental animals that will be used will be 280 Atlantic salmon and 8,400 copepodids (30 copepodids per fish). Design of experiment has been chosen to minmize number of individuals to be used , while maintaining statistical power and relevance.