R&D Manager Linda Andersen at ILAB presented results in January from a recently completed infection trial on Red Skin Disease (RSD) in Atlantic salmon. The trial was conducted at ILAB during the period November–December 2025.
The study is a collaboration between ILAB and the Fish Disease Research Group at the University of Bergen (Are Nylund, Heidrun Nylund, Christiane Trösse, Lindsey Moore, and Erwan Lagadec), and is supported by Halden Municipality and the Halden Watercourse Management Area.
The cause of Red Skin Disease has remained unknown since it was first described in Northern Europe in 2014. Since 2019, the disease has also been detected in Norway—particularly in the Enningdalselva river in Østfold. The condition is characterized by skin hemorrhages and ulcerations in wild Atlantic salmon. Several potential pathogens have been associated with the disease, but no causal relationship has yet been established.
In this trial, the aim was to investigate whether a co-infection involving different Aeromonas bacteria and the parasitic oomycete Saprolegnia parasitica could reproduce the disease phenotype. Following infection of sexually mature male salmon (1–3 kg), pathological changes consistent with RSD were observed. The results particularly indicate that Saprolegnia parasitica may play a more significant role in disease development than previously assumed.
The presentation attracted considerable interest, with approximately 40 participants representing a broad range of stakeholders—including County Governors, the Norwegian Veterinary Institute, the Norwegian Environment Agency, several river basin organizations (including Gaula and Numedalslågen), municipalities, hunting and fishing associations, research institutions (NINA, NMBU, UiB), as well as landowners and other stakeholders.
Further work is now underway to secure funding and establish a research consortium led by the Halden Watercourse Management Area, coordinated by Lars Selbekk.
Linda Andersen also presented the work at the Cultivation Seminar 2026 (KAF) in Trondheim, held March 16–18. The images below show cultured Saprolegnia parasitica and a wild Atlantic salmon affected by Red Skin Disease (photo: Bjarne Granli).
