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Q&A on the occurrence of Infectious Salmon Anaemia (ISA) in Shetland

Q1. How do we know it is ISA?

ISA is a disease which affects salmon in seawater.

ISA is identified through the incidence of:

  • High and persistent mortality
  • Characteristic visual signs
  • Identification of the disease agent which is a virus

ISA is diagnosed by reference to an internationally established diagnostic protocol. For all cases occurring within the EU the standard diagnostic definition used is defined in the EU fish health Decision No 2003/466/EC

Characteristic visual symptoms include darkening of the liver, severe anaemia, pale gills and visceral haemorrhage.

Q2. Does ISA affect wild fish?

Extensive testing of wild fish at the time of the outbreak in 1998-99 did find some evidence of ISA virus in salmonid species. The prevalence of infection was low. There was no evidence that it caused disease and no clinical signs were observed. There is no evidence from Norway, where ISA has been present since 1984, that ISA causes disease or harmful effects in wild Atlantic salmon.

Q3. Source of ISA infection?

This is under active investigation. The outbreak will be the subject of a scientific study to determine the source of the infection, the distribution of the disease in the environment and the risk of further spread (an 'epizootic study' of fish disease, equivalent to an epidemiological study of human disease incidence and transfer).

Q4. How is ISA transmitted?

ISA is transmitted between fish by direct contact, by infected blood, urine, other body fluids and faeces. Movements of live fish pose the greatest risk of spread of disease. Untreated effluent from processing plants has also been identified as being a particular risk.

There is no recognised risk of transmission between generations via eggs and this is reflected in fish health legislation.

Q5. What action has been taken to address the outbreak of ISA and to reduce the risk of further spread?

Official controls have been placed on the infected farms, the first of which was cleared of fish before confirmation of ISA, and other fish farm sites nearby, in the Control Zone. These have the effect of prohibiting the movement of all fish and fish eggs and, in the case of sites where a confirmed occurrence or official suspicion is in place, the movement of personnel, materials and equipment that could transfer virus to or from the Control Zone, without the express permission of Scottish Ministers. A number of other farms in the wider Surveillance Zone continue to be subject to official surveillance and health inspections on the movement of live fish.

The Fish Health Inspectorate of the Scottish Government has sent a team to Shetland to conduct detailed site inspections and sampling of all fish and sites in the Control Zone.

Q6. What next?

All sites in the control and surveillance zones will continue to be inspected by staff from Marine Scotland's Fish Health Inspectorate.

Q7. Have there been outbreaks elsewhere?

ISA disease has been widespread in Norway since the 1980s. Outbreaks have been reported in Canada and recent outbreaks in Chile have been particularly severe. The Faroe Islands' salmon farming industry was destroyed by ISA in 2000.

There has been one previous outbreak of ISA in Scotland in 1998-99 and was estimated by industry to have cost £30 million. It was significantly more widespread than the present outbreak and affected all fish farming areas of Scotland and the majority of fish farming companies. Prompt action to remove farmed fish from infected areas, with the co-operation of our salmon farming industry, succeeded in eradicating that outbreak.

The lessons learned from that outbreak have been incorporated in the salmon farming industry's Code of Good Practice.

Q8. Are there any risks to human health?

No. There is no history of any fish virus causing disease in humans. Fish are cold-blooded and research has shown that the ISA virus does not survive in (warm blooded) mammals and humans. ISA is not transferable to humans and poses no risk to human health.

Q9. What are we going to do to raise awareness?

We have briefed industry representatives, informed the media and have sent an information leaflet to all marine fish farmers in Scotland.

Q10. What is the impact on live salmon imports?

Importation of live salmonids is normally prohibited except from areas of equivalent health status.

Imports of live fish into Scotland have not been allowed from Norway, Chile or Canada as no salmon populations there satisfy the fish health requirements for import into the UK. Importation of salmon eggs is permitted provided the Official Service can certify that exporting farm is not subject to official controls for ISA or other serious diseases and the eggs are disinfected prior to dispatch.

Q11. What is the impact on exports of live salmon and salmon eggs from Shetland?

Salmon farming companies in the south-west area of Shetland have been advised that until further notice they cannot trade into areas or countries that are free of ISA.

Q12. What will happen to the dead fish?

Fish must be disposed of in accordance with the provisions of the EU Animal By-Products Regulation (EC) No 1774/2002, implemented in Scotland by the Animal By-Products (Scotland) Regulations 2003, SSI No 411/2003. The first preference is rendering. Other options are incineration and in remote areas deep burial. Ensiling, macerating in acid, is also employed to kill the virus.

On Shetland there is a licensed secure landfill site which takes receipt of ensiled fish and some fish are being incinerated.

Q13. How many fish farms are affected?

ISA has been confirmed on six sites which are close to each other. Movement restrictions have been applied to all farm sites within the Control Zone and a surrounding Surveillance Zone.

Q14. What will happen to fish in sites within the Control Zone?

Fish of marketable size may be authorised for moving to processing facilities for harvest. Those below harvestable size may continue to be grown out, or may be required to be slaughtered if ISA is confirmed on the farm.

Decisions will be taken in light of the scientific investigation of the prevalence and potential routes of spread of the disease.

Q15. Compensation

Compensation has been offered to one Shetland company which has had to destroy healthy fish as a result of ISA movement restrictions. The compensation offer will be subject to European Commission state aid approval.

Compensation will not be offered for ISA-affected fish stocks in line with practice in other salmon-producing countries in Europe. However European Fisheries Fund resources will be made available to affected small and medium-sized enterprises. Details of the scheme will be announced shortly.