Koi Herpesvirus and Pond Fish Welfare

Koi herpesvirus is a devastating disease that can kill entire pond populations within days, causing severe welfare harm and significant distress for both fish and their owners.

Key Facts

Koi herpesvirus (KHV) kills up to 100% of infected koi within 1-3 days of clinical signs
It is notifiable to the Environment Agency in England and Wales
Clinical signs include gill necrosis, lethargy, and skin lesions before rapid death
Temperature-dependent viral activity means outbreaks peak at 15-25 degrees Celsius
No licensed treatment exists - prevention through quarantine is the primary control
KHV spreads through water, shared equipment, and direct fish contact

Welfare Considerations

KHV causes rapid and severe welfare harm. Fish show respiratory distress as gill necrosis prevents oxygen uptake, then progressive failure before death within days of clinical signs. There is no treatment - affected fish either die or, if they survive subclinically, may become lifelong carriers. The welfare of KHV-affected koi is improved only by early euthanasia of severely affected individuals once the diagnosis is confirmed, preventing prolonged suffering. Prevention through biosecurity - quarantining new fish for 4-6 weeks before introducing them to established ponds - is the only effective welfare protection.

What You Can Do

Quarantine all new koi for 4-6 weeks before introducing them to established ponds
Test new fish for KHV using veterinary PCR testing before introduction
Report suspected KHV outbreaks to the Environment Agency as required by law
Never move pond water, equipment, or fish between ponds without disinfection
Seek veterinary guidance promptly at the first signs of fish disease