Guidance

Infectious haematopoietic necrosis (IHN)

How to spot Infectious haematopoietic necrosis (IHN), what to do if you suspect it and measures to prevent its spread.

Applies to England and Wales

Documents

Details

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  1. How to spot IHN
  2. How IHN is spread
  3. Preventing and controlling IHN
  4. Further information on IHN
  5. Legislation relating to IHN
  6. Who to contact if you suspect IHN

Infectious haematopoietic necrosis (IHN) is a viral disease predominantly affecting salmonid species. Outbreaks are most severe in fingerlings and juvenile fish. Serious outbreaks can result in losses of 95% or more. IHN may be carried by a range of freshwater and marine species of fish. More information on susceptible and vector species can be found here: Susceptible and vector species - 51²è¹Ý (www.gov.uk)

Great Britain (GB) is free from IHN and it is a ‘listed’ (also referred to as ‘notifiable’) disease which you are legally obligated to [report immediately to the Fish Health Inspectorate (FHI)], Cefas.Ìý

Historically IHN was only found in parts of North America. However, the disease has since spread to Europe and Asia through movement of infected fish and eggs. IHN has never been detected in GB.Ìý

It does not affect humans.Ìý

How to spot IHN

IHN typically occurs in water temperatures between 8°C and 15°.Ìý

Fish can appear lethargic with moments of frenzied and erratic swimming.ÌýÌý

Signs of the disease can include:Ìý

  • Behavioural changes such as lethargy mixed with frenzied, abnormal activity including spiral swimmingÌý
  • Trailing faecal castsÌý
  • Pale gillsÌý
  • Darkening of the skinÌý
  • Swollen abdomenÌý
  • Bulging eyesÌý
  • Areas of pinprick like bleeding e.g. at base of fins, around the head, and ventÌý

How IHN is spreadÌý

IHN can be spread through movements of infected fish, contaminated water, and contaminated equipment such as husbandry, angling and fish transport equipment and boats.ÌýÌý

Infected fish do not have to be sick or diseased to spread the virus.Ìý

Preventing and controlling IHNÌý

There is no treatment for IHN.ÌýÌý

Prevention is the best approach to controlling the disease. You can protect your fish by being aware of the signs of IHN and other serious diseases and checking stock health regularly.  Implement good husbandry and biosecurity practises, including surface disinfection of newly fertilised and eyed salmonid eggs using an appropriate method. Further information on biosecurity measures plans, guidance and templates can be found here: Biosecurity Measure Plans - Information and Templates - 51²è¹Ý (www.gov.uk) Ìý

You must be sure any fish introduced are IHN free. Do not buy fish of unknown origin. Follow the rules on moving aquatic animals: Aquatic animal health and movements guides - 51²è¹Ý (www.gov.uk)Ìý

You must report it to the FHI immediately if you notice or become aware of fish showing any of the signs of IHN. The FHI will investigate and apply disease control measures if required.Ìý

Further information on IHNÌý

IHN.Ìý

Legislation relating to IHNÌý

2009ÌýÌý

The listed diseases are in and Ìý

Who to contact if you suspect IHNÌý

If you suspect or know of a listed disease of fish and shellfish in England and Wales, you must report it immediately to the Fish Health Inspectorate (FHI), Cefas. You must also tell the FHI immediately if you know or suspect that increased mortality has occurred.ÌýÌý

Under the Aquatic Animal Health (England and Wales) Regulations 2009 it is a legal obligation to report suspicion of IHN in any farmed or wild fish to the FHI. It is an offence under the Regulations to fail to inform the FHI of suspicion of IHN.Ìý

  • ·¡³¾²¹¾±±ô: fhi@cefas.gov.ukÌý
  • Telephone: 01305 206700Ìý- Monday to Thursday - 9:00 am to 5:00 pm, Friday 9:00 am to 4:30 pmÌý
  • For emergencies out of hours telephone: 01305 206630Ìý

Fish Health InspectorateÌýÌý
Centre for Environment, Fisheries and Aquaculture Science (Cefas)Ìý
Barrack RoadÌýThe Nothe
Weymouth
Dorset
DT4 8UB

Updates to this page

Published 26 February 2024
Last updated 11 September 2024 show all updates
  1. Updated link to susceptible and vector species list.

  2. Vector and Susceptible species list updated from v1.1 to v1.2.

  3. Updated susceptible/vector species list.

  4. First published.

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