Studies on the pathology of ulcerative dermal necrosis (UDN) in Swedish salmon, Salmo salar L., and sea trout, Salmo trutta L., populations

• Published in: Journal of Fish Diseases
• Main Authors: JOHANSSON, N., SVENSSON, K. M., FRIDBERG, G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1982
• Subjects: Salmo salar
• Online Access: http://dx.doi.org/10.1111/j.1365-2761.1982.tb00485.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2761.1982.tb00485.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2761.1982.tb00485.x

Abstract. Continuous visual observations of the signs of development of UDN in fish kept in aquaria were correlated with light microscopical, transmission and scanning electron microscopical results. The initial signs of the disease are circles of pathologically‐changed epidermis. The tight junctions of the squamous cells within these mucus‐free areas disintegrate resulting in the loss of the protective function of the zonula occludens. Subsequently, the intercellular spaces dilate and communicate with the exterior. Necrosis of the epidermal cells due to hydromineral disturbances occur simultaneously with fungal infections and marked responses of the melanophores. It is suggested that the fungal infections are triggered by metabolites of the necrotic epidermal cells. The epidermal cells are shed and the fungus determines the further course of the disease which terminates in large ulcers covered with fungal hyphae. No substantial evidence for the presence of a virus could be recorded at any stage of the disease. It is concluded that the disease is a squames and the fungus appears as an opportunist which causes the eventual death of the fish.