Koi Herpesvirus (KHV) Disease
The Koi Herpesvirus (KHV) disease is a highly contagious viral disease for which there is no known cure and can result  in  death.  Koi that have been diagnosed with the KHV disease and recovered as well as those who have been exposed should be considered as carriers of the virus, as KHV remains in the infected fish for life.   The disease  has a mortality rate of between 80 to 100% occurs in water temperatures between 72 and 80 degrees.  Although KHV disease affects koi of various ages, it is the fry that have the greatest susceptibility.

Signs of KHV Disease 

Once your koi  becomes infected, death can start  within 24 to 48 hours.  The KHV infection may cause severe gill sores which appear as red and white patches.  The white patches are due to the death of the gill tissue.  The most common signs of KHV disease in koi are gill lesions.  Other signs include bleeding gills, eyes that are sunken, and pale patches or blisters on the skin.  In some cases, there may be a development of secondary bacterial and parasitic infections.  The infected fish may remain near the surface and swim listlessly.  They may also show signs of breathing difficulty and uncoordinated swimming.  At right is  picture of a Koi with KHV disease.


How KHV Disease Infects Koi

Ways of spreading the KHV disease including direct contact with the infected koi.  Other methods of transmitting the virus include fluids from the infected koi and water or mud that
have been exposed to the virus.  The KHV virus enters the koi through its gills.  Depending on the water temperature, susceptible koi fish may either become infected, develop the disease and die, or they may survive and become carriers of the virus.  Although still infected and capable of spreading the disease to other fish in your pond, your koi may never again show signs of the KHV disease.

Water Temperature and KHV Disease

Once infected fish have been mixed with the koi population in your pond there is an incubation period of approximately 14 days.  This period could be longer depending on the temperature of the water.  Death due to the KHV virus typically occurs between 72 and 78 degrees, with almost no deaths occurring below this range.  There is virutally no sign of KHV at or above 86 degrees.

Diagnosing KHV Disease

Although, a positive diagnosis of KHV will require either a veterinarian or a fish health specialist,  unless your koi of are high quality (some hobbysists have paid over $1,000 for one koi)  you probably won't want to do that.  The vet or specialist can perform diagnostic tests such as blood, fecal matter, mucus and gill biopsies, but even those tests may not be completely accurate.  As there is no treatment for KHV disease in Koi,  the best option is to take precautions  preventing it.

Preventing KHV Disease

Becoming familiar with your suppliers (my supplier is LiveAquaria.com) and having a good working relationship with them will go a long way in preventing the KHV virus from attacking your fish.   Before introducing your new koi to the general population of your pond, quarantine them away from the other fish. Use a separate system, ideally in a different area from your resident koi.  Always feed, handle and maintain your resident fish before the new koi.  The quarantined fish also require their own equipment such as nets, buckets, and siphon hoses that are used exclusively for them.  Quarantine them for a minimum of 30 days.  If at the end of the 30 day period your new koi show no signs of disease they can be added to the koi pond.