Puffy Skin Disease in Trout Fisheries – serious problem or over-inflated condition?
E.T. Nolan1,C.E. Maddocks2, S.W. Feist3, M. Crumlish2, R.H. Richards2 and C.F. Williams1
1 Environment Agency, National Fisheries Service, Brampton, England, UK; 2 Institute of Aquaculture, Stirling University, Stirling, Scotland, UK; 3 Centre for Environment, Fisheries and Aquaculture Science (Cefas), Weymouth laboratory, UK
Puffy skin disease (PSD) is an emerging skin condition of rainbow trout, Oncorhynchus mykiss (Walbaum) with unknown aetiology. Since 2009, there have been increased reports of PSD in UK fish farms and fisheries, with growing concern from both industry sectors. To ensure accurate diagnosis, avoid confusion with other skin conditions and promote prompt and consistent reporting, a case definition was developed combining clinical and pathological observations of diseased rainbow trout from both fish farms and fisheries. The defining features of PSD included pronounced lateral epidermal swellings with colour change and petechiae. Affected fish exhibited lethargy, loss of condition, inappetance and low level mortality. Histopathological changes were characterised by epidermal hyperplasia and spongiosis, oedema of the dermis stratum spongiosum and a mild diffuse inflammatory response. The distribution and characteristics of the disease in fisheries are presented along with management recommendations following outputs of a questionnaire and seasonal monitoring studies in still water trout fisheries. Prevalence and severity of skin lesions were shown to be greatest during late summer and autumn with evidence of clinical resolution during winter and early spring. A specific pathogen was not identified but an infectious aetiology is suspected. These studies represent the first comprehensive and comparative descriptions of PSD, with observations spanning both industry sectors in the UK. PSD holds important implications for the performance and economic viability of still water trout fisheries. Priorities for further research are discussed.
