Guidance: Viral haemorrhagic septicaemia (VHS)

Centre For Environment Fisheries Aquaculture Science

February 23
11:32 2024


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

Viral haemorrhagic septicaemia (VHS) is a viral disease mainly affecting rainbow trout. Other common species susceptible to VHS include brown trout, grayling, and pike, but it can cause disease in or be carried by numerous fish species both freshwater and marine, including turbot and herring. More information on susceptible and vector species can be found here: GB Lists of susceptible and vector species.

Great Britain (GB) is free from VHS, and it is a listed (also known as notifiable) disease which you are legally required to [report immediately to the Fish Health Inspectorate (FHI) at Cefas] Fish Health Inspectorate - GOV.UK (

VHS is considered the most serious disease of farmed freshwater rainbow trout causing very high levels of mortalities and may cause disease in all life stages of susceptible fish.

VHS was first reported in a rainbow trout farm in Denmark and the disease has since caused major losses in rainbow trout farms across Europe. There have been three outbreaks in GB since the early 1990s - in farmed turbot in 1994, in farmed rainbow trout in 1996, and in multiple species of wrasse in sea-water farms in 2012. All these outbreaks were controlled, and the disease eradicated from GB.

It does not affect humans.

How to spot VHS

VHS generally occurs in temperatures of 14C or below, typically in the spring months.

Often fish will appear lethargic and dark in colour and will be found in the margins and water outlets and typically, diseased fish will not attempt to escape when netted.

Signs of the disease can include:

  • rapid onset of mortalities
  • pale gills
  • lethargy
  • darkening of the skin
  • swollen (fluid-filled) abdomen
  • bulging eyes
  • signs of bleeding around eyes and base of fins, gills and skin
  • gasping at the surface
  • abnormal swimming in spiralling patterns or flashing

How VHS is spread

VHS is 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 VHS

There is no treatment for VHS.

Prevention is the best approach to controlling the disease. You can protect your fish by being aware of the signs of VHS 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 (

You must be sure any fish introduced are VHS free. Do not buy fish of unknown origin. Follow the rules on moving aquatic animals: Aquatic animal health and movements guides - GOV.UK (

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

Further information on VHS

World Organisation for Animal Health (WOAH) Aquatic Manual chapter VHS.

Legislation relating to VHS

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 VHS

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 VHS in any farmed or wild fish to the FHI. It is an offence under the Regulations to fail to inform the FHI of suspicion or knowledge of VHS.

  • Email:?
  • 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

Published 23 February 2024

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