Cold water as a delousing treatment: effect on sea lice and salmon mortality
FHF’s objective is to develop new methods to prevent and control sea lice infestations without the use of chemotherapeutants. In recent years, a number of non-chemotherapeutants delousing methods have been developed, including the use of fresh water and warm water. These methods are not 100% effective in removing lice, and do not kill all lice.
Recent research by Overton et al. (2017) published in Pest Management Science demonstrated that during hydrogen peroxide treatment against lice, decreased treatment temperature relative to ambient temperature potentially assisted in lice removal and reduced salmon mortality rates. This preliminary research suggested that temperature shock could possibly play a role in lice removal. Many well-boats are equipped with refrigerated seawater (RSW) machines that can produce cold water. Therefore, if cold-water delousing is a successful treatment strategy, treatment could be easily implemented with minimal technological development.
Before cold-water delousing can be approved as a treatment, we need to determine how great temperature changes must be and for what duration to apply them to create a treatment effective against the various sea lice lifecycle stages. Further, we must understand how rapid decreases in temperature and different treatment durations influence salmon welfare.
The aim of the experiment is to determine if cold-water treatment is a viable delousing treatment that can be administered to maximise salmon lice removal and ensure there are no severe post-treatment outcomes for salmon. By treating salmon with different long-term (30 and 240 min) and short-term (30 sec, 1 min and 3 min) treatment durations at different cold-water temperatures, we can determine the effects of treatment duration as well as treatment temperature on salmon welfare and lice removal. Using 400 fish, we will have a total of 10 different treatment groups, each with different treatment temperatures and treatment length performed in triplicate. To determine lice removal efficacy, 10 fish from each treatment will be used (10 treatments x 3 replicates + 100 fish to determine lice loads before treatment = 400 fish). A further 30 post-smolt salmon will be used to produce lice eggstrings during the infection period.
Recent research by Overton et al. (2017) published in Pest Management Science demonstrated that during hydrogen peroxide treatment against lice, decreased treatment temperature relative to ambient temperature potentially assisted in lice removal and reduced salmon mortality rates. This preliminary research suggested that temperature shock could possibly play a role in lice removal. Many well-boats are equipped with refrigerated seawater (RSW) machines that can produce cold water. Therefore, if cold-water delousing is a successful treatment strategy, treatment could be easily implemented with minimal technological development.
Before cold-water delousing can be approved as a treatment, we need to determine how great temperature changes must be and for what duration to apply them to create a treatment effective against the various sea lice lifecycle stages. Further, we must understand how rapid decreases in temperature and different treatment durations influence salmon welfare.
The aim of the experiment is to determine if cold-water treatment is a viable delousing treatment that can be administered to maximise salmon lice removal and ensure there are no severe post-treatment outcomes for salmon. By treating salmon with different long-term (30 and 240 min) and short-term (30 sec, 1 min and 3 min) treatment durations at different cold-water temperatures, we can determine the effects of treatment duration as well as treatment temperature on salmon welfare and lice removal. Using 400 fish, we will have a total of 10 different treatment groups, each with different treatment temperatures and treatment length performed in triplicate. To determine lice removal efficacy, 10 fish from each treatment will be used (10 treatments x 3 replicates + 100 fish to determine lice loads before treatment = 400 fish). A further 30 post-smolt salmon will be used to produce lice eggstrings during the infection period.