Red skin disease 2019: summary

During the late spring and summer of 2019  the Fish Health Inspectorate received a number of reports of moribund adult wild Atlantic salmon being observed in Scottish rivers. Clinical signs of disease included skin damage, such as petechial haemorrhaging on the ventral surface and ulcer like lesions. Fungal-like infections were also reported in addition to inflamed red vents. Similar reports were also being made in Norway and Ireland.

Where moribund fish were observed, could be caught and kept alive, Fish Health Inspectors attended and took a range of  diagnostic samples. In total twelve individual diagnostic cases were completed, sampling fish from ten rivers including the Rivers Helmsdale, Halladale, Naver, Dee, Conon, Cassley, Forss, Nith, Garry and Little Gruinard.

In addition twenty three reports were received of fish displaying similar clinical signs of disease from the Rivers Alness, Clyde (Blantyre), Findhorn, Carron (Dounie), Helmsdale, Spey, Annan, Tweed, Don, Dee, Ness,  North and South Esk, Awe, Nairn, Inver and Nith.

From the samples taken we did identify a number of pathogens and associated pathologies, however, there was nothing conclusive and no causative agent was identified to explain the morbidity and clinical signs of disease.

Scientists from the Disease Diagnostic Group, which acts as the Scottish National Reference Laboratory for fish diseases, have been liaising with colleagues across the north Atlantic region to try to identify the causative factor(s) behind ‘red skin disease’. Clinical, diagnostic and epidemiological data will be shared across various laboratories and a clinical case definition will be established.

Following completion of any case it is published on our website, this includes observations, lab results and diagnostic reports, you will find these on the 2019 case information page.

The relevant diagnostic cases are:

• 20190072 (River Dee)
•  20190186 (River Conon)
•  20190189 (River Cassely)
• 20190212 (River Helmsdale)
• 20190287 (River Halladale)
• 20190288 (River Naver)
• 20190296 (River Garry)
• 20190297 (River Dee)
• 20190306 (River Dee)
• 20190322 (River Forss)
• 20190348 (Little Gruinard)
• 20190408 (River Nith).