Scotland's wild Atlantic salmon, once abundant, are now endangered. Populations are at their lowest levels ever, and urgent action is needed to safeguard them from fish diseases, parasites, and invasive species. Once introduced, disease, parasites, and invasive species become increasingly difficult to eradicate.  

Here you’ll find essential information on biosecurity measures, fish disease reporting, and invasive species identification to help you take action. 

Diseases

Impact on wild salmon: Saprolegnia is a water mould that causes skin infections in both salmon and trout. Light infections may look unsightly but are usually tolerated by healthy fish and can heal if conditions allow. Saprolegnia in general is a secondary opportunistic pathogen that will infect fish that have physical damage on the skin or are immunocompromised. However, some species, like Saprolegnia parasitica, are considered primary pathogens because they can cause systemic diseases leading to debilitation, lethargy and even mortality of badly infected fish. Rising water temperatures, a result of climate change, have been linked to increased frequency and severity of outbreaks.

Current Status in Scotland: Saprolegnia is ubiquitous in the environment and Outbreaks have been reported in several rivers across Scotland.

How to Identify:

  • White, cream or pale brown cotton wool-like growths on the skin and fins of fish
  • These infections often start as small round patches, but can increase in size to form larger plaques covering the body
  • Fish with severe infection  may appear lethargic or moribund.
  • Skin damage or lesions, often near infected areas, particularly around the head and fins.

Parasites

Impact on Wild Salmon: Gyrodactylus salaris (Gs) is a microscopic parasite that infects the skin and gills of juvenile salmon. Once introduced, it spreads quickly, causing mass mortality in affected populations, and is extremely difficult and costly to eradicate. Gyrodactylus salaris can be spread between and from rainbow trout farms through stocking practices.  

Current Status in Scotland: GS has never been identified in Scotland health zone and we are currently disease free. However, Scotland remains vigilant in preventing the introduction of Gyrodactylus salaris. Biosecurity measures are in place, but the parasite poses a significant risk if it ever enters the country’s rivers. 

How to Identify: 

  • Small, barely visible parasites on the skin and gills of juvenile salmon. 
  • Fish may appear stressed and weakened. 
  • Visible damage to the gills. 

 

Invasive Non-Native Species

Impact on wild salmon: Pink salmon is an invasive non-native species which could compete with Atlantic salmon for habitat and food. There is also a risk that it could spread disease to native species. 

Current Status in Scotland: Reports of pink salmon are increasing in Scottish rivers, and efforts are underway to monitor their spread and potential impact. 

How to Identify: 

  • Large black oval spots on the tail. 
  • Dark mouth. 
  • In freshwater, male pink salmon develop a distinctive hump. 

What can you do?

Report

 

Use our app or online tool to report sightings of pink salmon, other invasive species, or signs of fish disease. Early detection is critical to controlling their spread and safeguarding wild fish populations.

 

 

 

 

Adopt Biosecurity Measures

 

Prevent the spread of diseases and invasive species by following these simple biosecurity steps:

 

Check: Inspect your equipment, clothing, and boats for debris, plants, and animals before moving between water bodies.

Clean: Wash off any material thoroughly, using hot water or disinfectant if possible.

Dry: Ensure everything is completely dry before reuse. Invasive species can survive in damp conditions for weeks.