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
Contents
- How to spot IHN
- How IHN is spread
- Preventing and controlling IHN
- Further information on IHN
- Legislation relating to IHN
- 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: GB Lists of susceptible and vector species.
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.
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.
It does not affect humans.
How to spot IHN
IHN typically occurs in water temperatures between 8°C and 15°.
Fish can appear lethargic with moments of frenzied and erratic swimming.
Signs of the disease can include:
- Behavioural changes such as lethargy mixed with frenzied, abnormal activity including spiral swimming
- Trailing faecal casts
- Pale gills
- Darkening of the skin
- Swollen abdomen
- Bulging eyes
- Areas of pinprick like bleeding e.g. at base of fins, around the head, and vent
How IHN is spread
IHN can be spread through movements of infected fish, contaminated water, and contaminated equipment such as husbandry, angling and fish transport equipment and boats.
Infected fish do not have to be sick or diseased to spread the virus.
Preventing and controlling IHN
There is no treatment for IHN.
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 - GOV.UK (www.gov.uk)
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 - GOV.UK (www.gov.uk)
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.
Further information on IHN
World Organisation for Animal Health (WOAH) Aquatic Manual chapter IHN.
Legislation relating to IHN
The Aquatic Animal Health (England and Wales) Regulations 2009
The listed diseases are in Regulation 1251/2008 as amended by the Animals, Aquatic Animal Health, Invasive Alien Species, Plant Propagating Material and Seeds (Amendment) (EU Exit) Regulations 2020, at Chapter 2, Annex 1A and Schedule 1 of The Aquatic Animal Health (England and Wales) Regulations 2009
Who to contact if you suspect IHN
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.
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.
- Email: fhi@cefas.gov.uk
- Telephone: 01305 206700 - Monday to Thursday - 9:00 am to 5:00 pm, Friday 9:00 am to 4:30 pm
- For emergencies out of hours telephone: 01305 206630
Fish Health Inspectorate
Centre for Environment, Fisheries and Aquaculture Science (Cefas)
Barrack Road The Nothe
Weymouth
Dorset
DT4 8UB