About koi herpesvirus

Koi herpesvirus (KHV) is a virus that affects only carp, koi and goldfish.

KHV has spread to North America from other parts of the world. This invasive fish virus was:

  • first found in 1999 in the United States
  • probably introduced to Ontario waters via the hobby fish trade

How to identify KHV

Infected fish may show the following signs:

  • patches of discolouration on skin
  • swollen, pale and rotting gills
  • sunken eyes and notch on the nose of the fish
  • excess mucus early in disease, and loss of mucus in late stages of disease
  • appetite loss and erratic swimming

Other fish diseases can show these signs. Laboratory tests can diagnose koi herpesvirus.

People and koi herpesvirus

Koi herpesvirus is not a risk to human health:

  • the virus does not affect humans
  • carp infected with KHV are safe to eat and handle

However, it is never wise for people or pets to consume or handle fish that:

  • look sick
  • are dying
  • are already dead

Where KHV has been found

The virus has been found in wild carp in south-central Ontario including:

  • Chemong Lake
  • Lake Simcoe and connecting rivers
  • Otonabee River
  • Rice Lake
  • Lake Scugog
  • Pigeon Lake

Disease outbreaks

Koi herpesvirus is highly contagious and has been linked to large fish die-offs. Fish are most susceptible when crowded or spawning. Water temperature is also a key factor, with:

  • disease and death most common in water temperatures between 18°C and 28°C
  • rare outbreaks in temperatures below 13°C

KHV passes from fish to fish by:

  • close contact
  • entering the gills and possibly the intestine

The virus survives in:

  • diseased fish
  • fish that carry the virus after surviving an outbreak
  • water for short periods of time (4-24 hours)
  • feces and the mud bottoms of lakes and rivers (possibly)

How to prevent disease outbreaks

Outbreaks of koi herpesvirus in the wild are almost impossible to prevent or treat.

Minimize outbreaks in cultured koi or goldfish by:

  • buying from a reputable supplier
  • quarantining new fish before introducing them to ponds or aquariums

Do not flush sick or dead goldfish or koi down the toilet. Instead:

  • humanely kill sick goldfish or koi
  • bury or compost dead fish, or put them in the garbage

For more information

For general inquiries, call the Natural Resources Information Support Centre: 1-800-667-1940

To report fish die-offs, call: 1-866-929-0994

What to do about a fish die-off