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Farmed and wild salmonids are affected by a variety of skin conditions, some of which have significant economic and welfare implications. In many cases, the causes are not well understood, and one example is cold water strawberry disease of rainbow trout, also called red mark syndrome, which has been recorded in the UK since 2003. To date, there are no internationally agreed methods for describing these conditions, which has caused confusion for farmers and health professionals, who are often unclear as to whether they are dealing with a new or a previously described condition. This has resulted, inevitably, in delays to both accurate diagnosis and effective treatment regimes. Here, we provide a standardized methodology for the description of skin conditions of rainbow trout of uncertain aetiology. We demonstrate how the approach can be used to develop case definitions, using coldwater strawberry disease as an example.

Simultaneous reports were received between June and July 2007 of wild Atlantic salmon Salmo salar with red, swollen, bloody vents returning to geographically diverse rivers in Scotland. By the end of September the condition, colloquially known as 'red vent syndrome' (RVS), was reported from > 50 rivers across Scotland. Fish were generally in good overall condition but the vent area showed mild to severe lesions. External characteristics of the syndrome included a swollen, raised, haemorrhagic vent and surrounding tissues, with erosion of the skin, scale loss and moderate to severe bleeding in more advanced cases. Predominantly, the fish affected were 1-sea-winter grilse; however, RVS was also recorded in 2-sea-winter salmon and sea trout S. trutta. High numbers of the nematode Anisakis Type I larvae were found infesting the discrete region of the vent, a localisation that is reported as novel for the parasite. The hypothesis that this is a different species than that commonly found in the body cavity and viscera was investigated through molecular studies. These studies failed to show evidence that the parasites infesting the vent were different from those in the body cavity, i.e. all were identified as A. simplex sensu stricto. No other disease agent was found associated with the lesions or was isolated systemically, and no mortality or prevention of spawning was recorded during the 2007 season. Possible causes, including warming environments in the North Atlantic, are hypothesised as playing a role in the development of RVS in Atlantic salmon.

Viral haemorrhagic septicaemia (VHS) is an infectious disease of farmed and wild fish and has an extensive host range in both freshwater and marine environments. In December 2012, a wrasse population consisting of ballan, Labrus bergylta (Ascanius), corkwing, Symphodus melops (L.), cuckoo, Labrus mixtus L., goldsinny, Ctenolabrus rupestris (L.), and rock cook, Centrolabrus exoletus (L.), held at a marine hatchery in the Shetland Isles, Scotland, experienced a mortality event. Approximately 10 000 wrasse were being held at the facility on behalf of an Atlantic salmon, Salmo salar L., aquaculture company prior to being deployed for the biological control of parasites on marine pen Atlantic salmon, aquaculture sites. Fish Health Inspectors from Marine Scotland Science initiated a diagnostic investigation, and subsequent diagnostic testing confirmed the site to be VHSV positive by qRT-PCR and virus isolation followed by ELISA. A VHSV genotype-specific qRT-PCR assay revealed that the isolates belonged to genotype III, the European marine strain of the virus. The virus genotype was further confirmed by nucleic acid sequencing of the partial nucleoprotein (N) and glycoprotein (G) genes followed by BLAST nucleotide searches. This study reports for the first time the detection of VHSV within multiple wrasse species and highlights the need for a comprehensive risk-based approach to the use of wrasse and other finfish species as biological controls within the aquaculture industry.

Cardiomyopathy syndrome (CMS) has been recorded in wild and farmed Atlantic salmon Salmo salar. Characteristic heart lesions primarily involving the myocardium are reported in natural outbreaks with associated mortality. To date, no experimental trials have reproduced these lesions in the laboratory. The present study reports on the first successful experimental transmission of CMS in Atlantic salmon in Scotland, with full development of the histological lesions that are described for the syndrome. Tissue homogenates of CMS-infected fish indicative of mild and severe lesions from Scottish and Norwegian natural outbreaks, respectively, were injected into naïve fish, and both induced heart lesions consistent with CMS. Lesion development was earlier and progression faster in the fish group receiving the Norwegian homogenate, but equivalent in both groups by the end time point of the experiment. The study demonstrated that the reported condition for both countries is identical, as evaluated through light microscopy, and that tissue homogenates from either mild or severely affected fish contain the transmissible agent. KEY WORDS: Cardiomyopathy syndrome · Atlantic salmon · TransmissionResale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESS

Common dab Limanda limanda from Scottish and international waters were examined by quantitative real-time RT-qPCR for evidence of viral RNA consistent with salmonid alphaviruses (SAV). SAV prevalence in heart tissue varied between sampling sites and reached up to 17% in fish collected near the Shetland Islands, Scotland. Raw Ct values ranging from 22.31 to 39.45 were obtained from the SAV-positive tissue material using the nsP1 RT-qPCR assay. Bayesian-, likelihood-and distance-based phylogenetic analyses performed with the amplified partial E2 gene sequence dataset suggest that the dab-derived virus belongs to SAV Subtypes I, II and V. A single SAV subtype was identified from the majority of sampling sites, apart from Shetland, where Subtypes II and V were also identified. The presence of SAV RNA from common dab in regions detached from salmon aquaculture lends support to the hypothesis that common dab are bone fide wild reservoirs of SAV, independent of fish farming activity. There was no link between the occurrence of viral RNA, length and sex of the dab, water depth, or health status as recorded using the International Council for the Exploration of the Sea (ICES) guidelines. In addition, the histological changes recorded in dab could not, with certainty, be attributed to infection with SAV. Finally, and for the first time, this study demonstrated that the dab-derived SAV Subtype V virus could be successfully cultured in a salmonid cell line.

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An increasing trend in the prevalence of hyperpigmentation in the common dab Limanda limanda from the North Sea prompted us to investigate the potential role of infectious agents as causes or contributing factors to the condition. Dab representing 3 severity grades of hyperpigmentation were sampled for virology, bacteriology, histopathology and ultrastructure assessments. No cytopathic effect was recorded during virology testing, and bacteriological results showed no differences between normal and hyperpigmented dab. Histopathological assessment showed that the most significant changes occurred in the dermis as a result of chromatophore hyperplasia, namely melanophores and iridophores, alongside loose melanin granules. Dermal lymphocytic infiltration occasionally expanding into the epidermis and the underlying musculature was more frequent in highly pigmented dab than in normal fish, suggesting an active immune response. Ultrastructure studies showed additional disruption of the epithelial layer, with loose melanin granules between cells and a number of single or aggregated melanocytes. Dab representing different grades of hyperpigmentation kept in the laboratory alongside normal fish for a monitoring period of 18 mo showed no changes in their pigment distribution pattern, nor occurrence of new pigment in the normal fish. The current investigation found no association of hyperpigmentation in the common dab with infectious agents; therefore, understanding the cause of the condition remains a challenge which can now more reliably focus on a non-infectious origin hypothesis.