Epizootic haematopoietic necrosis (EHN)
How to spot Epizootic haematopoietic necrosis (EHN), what to do if you suspect it and measures to prevent its spread.
Applies to England and Wales
Documents
Details
Contents
- How to spot EHN
- How EHN is spread
- Preventing and controlling EHN
- Further information on EHN
- Legislation relating to EHN
- Who to contact if you suspect EHN
Epizootic haematopoietic necrosis (EHN) is viral disease of Rainbow trout and European perch.
It causes low level losses in Rainbow trout therefore infections can go unrecognised. However, this disease can cause large scale mortalities in the European perch.
More information on susceptible and vector species can be found here: GB Lists of susceptible and vector species.
Great Britain is free from this virus, 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.
There has never been a recorded outbreak of EHN in the UK
It does not affect humans.
How to spot EHN
EHN typically causes clinical disease in water temperatures between 11-20°C. Poor husbandry and water quality appear to be related to outbreaks within rainbow trout farms.
EHN causes behavioural changes in the fish including buoyancy issues and loss of appetite.
Signs of the disease can include:
- General poor health
- Darkening of the body surface
- Fin rotting
- Discolouration
- Weak swimming
- Swollen Spleen or liver
How EHN is spread
EHN is spread through contact with infected fish or water.
EHN 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 EHN
There is no known treatment for EHN.
Prevention is the best approach to disease control. You can protect your fish from by being aware of the signs of EHN and other serious diseases and checking stock health regularly. Implement good husbandry and biosecurity practises.
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 EHN 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 EHN. The FHI will investigate and apply disease control measures if required.
Further information on EHN
World Organisation for Animal Health (WOAH) Aquatic Manual chapter EHN.
Legislation relating to EHN
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 EHN
If you suspect or know of a listed disease of fish or 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 EHN in any farmed or wild fish to the Fish Health Inspectorate. It is an offence under the Regulations to fail to inform the FHI of suspicion of EHN.
- 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