Photo: Jannicke Wiik Nielsen, Norwegian Veterinary Institute

Wild salmon in Norwegian watercourses is threatened by infection with the parasitic salmon fluke (Gyrodactylus salaris). The parasite attaches to the fish and feeds on the skin by releasing a digestive solution with proteolytic enzymes. Mucus and dissolved skin are then sucked into the gut of the parasite. Mortality of salmon infected with multiple salmon flukes is high. Eradication of the parasite in Norwegian rivers and lakes is therefore a prioritised goal. Several approaches for water treatment have been tested, including the use of the plant toxin rotenone, which is killing not only the salmon fluke, but also the fish and other water organisms. Methods that are more selective are required. An ongoing project at the Norwegian Veterinary Institute is exploring the use of chlorine for this purpose. The aim is to find the optimal concentration that is sufficient to kill effectively the parasites, while it has the least possible impact on the salmon. In this context, changes in the physiological composition of the skin mucus are an indicator for fish welfare. Mass spectrometry-based proteomics and metabolomics are used to monitor differences between groups of chlorine-treated and control salmon. Up- and down regulation of proteins and small metabolites depending on the treatment and exposure period can be observed.

The project is performed in cooperation between the Norwegian Institute for Water Research and the Norwegian Veterinary Institute, on behalf of the Norwegian Environment Agency. Results are published as a report.

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