Abstract
Samples from moribund lumpfish were collected in a marine hatchery in Scotland in 2015. Black nodules were noted on the skin, and gills and fungal hyphae were extensively distributed in musculature and internal organs. Multifocal chronic inflammatory lesions displaced structures in all affected organs. Mortalities commenced on completion of spawning in May and were evenly distributed over the second year in the temperature range 11–15°C. The main systemic infection causing agent was initially identified based on morphological characteristics as an Exophiala species. Ribosomal DNA (rDNA) ITS regions of the isolates were subsequently sequenced confirming the isolates belonged to Exophiala genus. All isolates fell in a single phylogenetic cluster, which is represented by Exophiala angulospora. Fish were treated with either formalin or Bronopol or a combination of both, but there was no effect on the pattern or numbers of mortalities. Isolates were also tested against three different concentrations of Latrunculin A, Amphotericin B and Itraconazole with no success. It is of utmost importance to increase the knowledge on pathogen–host interactions to successfully develop sustainable control methods.
Highlights
One of the major health problems that the Atlantic salmon (Salmo salar) industry faces at the sea farming stage is the sea louse, Lepeophtheirus salmonis Krøyer. This ectoparasite attaches to fish skin and mucosa (Boxaspen, 2006) inducing lesions that lead to a loss of body fluid and can be a point of entry for secondary pathogens and stress that may result in fish mortality if untreated (Denholm et al, 2002; Johansen et al, 2011)
Live feed is the first feed of many marine finfish larvae but Artemia nauplii are only required briefly in lumpfish farming before transition to dry formulated feed, and many hatcheries have eliminated live feed altogether
It has been suggested that the ex‐ tent of host specificity is low and has extended beyond marine finfish to a range of cold‐blooded animals including amphibians, tortoises and crabs
Summary
One of the major health problems that the Atlantic salmon (Salmo salar) industry faces at the sea farming stage is the sea louse, Lepeophtheirus salmonis Krøyer. This has given good results but there is concern for wild stocks, about possible bi‐ osecurity risks of sourcing eggs from wild‐caught fish, and there has been a desire to move to use broodstock from hatchery reared pro‐ duction (Jonassen, Lein, & Nytrø, 2018; Wittwer & Treasurer, 2018) This will minimize the requirement for wild stocks, allow access to disease free, established photoperiod controlled stocks to enable year‐round production and to permit the initiation of breeding programs to select for disease resistant fish and primarily to identify families with high levels of cleaning activity. Fungal mycoses in fish are common but most affect external tissues with few species found in internal organs (Verma, 2008) These reports identified the main agent of mycosis in lumpfish as Exophiala sp. The current work examines the clinical signs of disease, identification of the fungus, epidemiology of infection and means of treatment and management of Exophiala angulospora infection
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