Systemic mycoses in lumpfish (Cyclopterus lumpus L.) in Ireland: aetiology and clinical presentation

Systemic infections with predominantly Exophiala species have emerged as regular and significant pathogens of lumpfish in Ireland and abroad. Exophiala is a genus of melanised fungi in the order Chaetothyriales. They are regularly found as opportunistic pathogens of cold blooded vertebrates and several species have caused high mortalities in aquaculture. In 2016 and 2017, E. angulospora, E. psychrophila, E. salmonis and a Cyphellophora sp. were identified as the causes of phaeohyphomycosis in lumpfish in Ireland, as confirmed through clinical presentation, histopathology, wet mounts, fungal culture, sequencing of the ITS region and phylogenetic analysis. Systemic pathology was severe, characterised by segmented, pigmented hyphae in the host tissues associated with severe necrosis and inflammation. Significant chronic mortality in lumpfish broodstock in Ireland was attributed to E. angulospora and E. psychrophila. E. angulospora was also isolated from cases with multiple infectious aetiologies. E. salmonis and a Chyphellophora sp. were diagnosed in lumpfish at sea. This is the first record of E. salmonis in lumpfish.