Salmon skin damage and disease 2019

Over the last week or two many reports of disease in wild adult salmon populations have been reported. These reports have been widespread ranging from Scotland to Scandinavian. The common factor is death through fungal infection (Saprolegnia). Nothing new there you may say but the difference this year is the focus of the fungal infection along the underside of the fish. There is evidence from northern Scottish rivers that the fungal infection is preceded by what looks like a rash on the underside of the fish with associated haemorrhaging. In the rivers with the worst incidences there have been large losses from fungal infection, whilst in others there is no fungal infection, yet.

Salmon exhibiting what appears to be the characteristic rash on the underside.

A fish with more subtle marks on the underside. My first thought on seeing marks like this would be running damage but I am assured by those on who have seen it in the flesh that this is something different, something more worrying (Photo: Peter Quail).

Fresh run salmon appear to be entering rivers carrying rash like marks on their underside, leaving them susceptible to fungal infection. If fish with this skin damage become infected with fungus death occurs quickly. It also looks as if only the recent arrivals have been affected with the no sign of it in the older fish.

Helmsdale fish with fungal infection along the underside

.

To lose some of the spring stock to fungus is not unusual in the Spey, especially the May fish, which always seem the most susceptible. However, affected fish normally have patches of fungus on the head, gills, back and fins, as in the example below.

A Spey salmon, from 2012, with the typical distribution of fungus on the head, back, fins and underside (Photo: Mark Melville) . We may be reading too much into what may just be subtle differences in the distribution of the fungus infection but those who have seen it consider it to be different.

Fishery managers in the northern rivers, which seem to be the worst affected at present, have been admirably open about the situation and proactive with sampling and analysis. Indeed I have just heard that the Marine Lab Fish Health Inspectors have returned negative results for the viral and histology samples from Helmsdale fish. The Helmsdale managers are also organising for infected fish to be sampled to assess Thiamine levels. There are various reports of Thiamine deficiency affecting ecosystems, in the Baltic for example. A link between the disease outbreak in 2019 with Thiamine deficiency has yet to be established.

So far there have been no affected fish reported from the Spey but that may change. Those who have experienced this disease in the last few weeks are understandably worried. We hope that this will turn out to be a temporary problem which will clear up as the summer progresses. In the past, a summer spate, as we have seen on the Spey in the last two weeks, usually clears up fungal problems very quickly, with no recurrence again until the autumn. In the meantime we are asking ghillies and anglers to photograph fish with unusual marks on the belly. Fish health inspectors will be called if required.

If anyone wishes further information, or to discuss, please do not hesitate to call the Spey Fishery Board office.

Authored by: Brian Shaw

There are 3 comments for this article
  1. Norman Murray at 8:53 pm

    It maybe thiamine deficiency, has any fish been tested for this, the fungal growth may be a secondary in fection?

    • Brian Shaw Author at 9:44 pm

      Norman, that is one theory. I know that fish from one of the rivers up north have sent fish for testing for thiamine. but not heard any results yet. The fungal growth is always secondary to the primary cause, which is often skin damage. Still no reports from the Spey, fingers crossed! Thanks for the comment

  2. Paul Rankine at 2:41 am

    Looks like a blood related disease. Any links with farmed salmon diseases or indeed sea lice diseases ?

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.