Ulcerative dermal necrosis (UDN), a chronic skin condition, affects primarily mature wild salmonids returning from the sea to freshwater for their spawning. The involvement of water moulds such as Saprolegnia parasitica as a secondary pathogen in this disease is clear but the identification of a primary cause or of primary pathogen(s) remains elusive. In this opinion article, we re-visit UDN regarding epidemiology, pathology and aetiology and speculate the potential involvement of UV radiation in the initiation of UDN in salmonid fish returning from the sea.

中文翻译：

---

大西洋鲑鱼的溃疡性皮肤坏死 (UDN) 是否可以归因于紫外线辐射和继发性水霉属寄生虫感染？

溃疡性皮肤坏死 (UDN) 是一种慢性皮肤病，主要影响从海洋返回淡水产卵的成熟野生鲑鱼。水霉等水霉作为该疾病的次要病原体的参与是明确的，但主要病因或主要病原体的鉴定仍然难以捉摸。在这篇观点文章中，我们重新审视了 UDN 的流行病学、病理学和病因学，并推测紫外线辐射可能参与了从海中返回的鲑鱼中 UDN 的启动。