Guidance: Koi herpesvirus (KHV)

How to spot koi herpesvirus (KHV), what to do if you suspect it and measures to prevent its spread.

Koi herpesvirus (KHV) is a contagious viral disease of common carp (Cyprinus carpio) including mirror carp, leather carp, koi carp and ghost carp. It can cause high mortality.

Infected fish may not show clinical signs and the virus can persist in populations at low levels within populations. Disease outbreaks are typically triggered by stress and environmental conditions such as high temperature.   

KHV is a listed disease (also known as a ‘notifiable’ disease) of both farmed and wild fish. Further information on KHV susceptible and vector species can be found in our guidance.  

In England and Wales if you suspect KHV in any farmed or wild fish you must report it immediately by contacting the Fish Health Inspectorate (FHI) at the Centre for Environment, Fisheries and Aquaculture Science (Cefas) by calling: 

For urgent enquiries, including reporting disease suspicion, a 24/7 on-call service is available via this number.

You must also tell the FHI or a veterinarian immediately if you know or suspect that increased mortality has occurred.   

If you do not report it, you’re breaking the law.

KHV disease occurs at water temperatures between 16°C and 29°C. Stress events can trigger outbreaks. Affected fish often become lethargic and gather at water inlets or in the shallows.   

Patches of dead (necrotic) tissue in the gills, often with secondary fungal or bacterial infection. Gills may also appear pale   

Appearance of bleeding on skin and base of fins  

Patchy pale colouration or reddening of the skin 

KHV is spread through contact with infected fish or water. The virus is released via faeces, urine, gills and skin.   

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

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