Koi Herpes Virus (KHV) / Gill Rot


Koi herpes virus (KHV) is a viral disease that is very contagious to the common carp Cyrpinus carpio. It is most common found in ornamental koi, which are often used in outdoor ponds or as feeder stock. The first case of KHV was reported in 1998, but not confirmed until later in 1999.

KHV is a DNA-based virus. After discovery, it was identified that KHV is indeed a strain of herpes virus. Like other strains, KHV stays with the infected fish for the duration of their life, making the recovered and exposed fish potential carriers of the virus. Koi fish infected with KHV may die within the first 24-48 hours of exposure.

KHV is listed as a non-exotic disease of the EU and is therefore watched closely by the European Community Reference Laboratory for Fish Diseases.


The fish will display some or all of these signs: Open sores, fin rot, either caused by Aeromonas, or Pseudomonas bacteria, a clear to whitish or yellow film over the eyes, and a beige to yellowish green or brown mucoid substance on the wounds, skin, or gill area.  Most people think that this substance is a fungus, but it is a mucous that comes out of the skin from the virus

mostly KHV symptoms are:

  • Gill mottling
  • Red and white patches appearing on gills
  • Bleeding gills
  • Sunken eyes
  • Pale patches
  • Blisters


The only effective way to treat fishes that are infected with K.H.V. is with heat therapy.  You must have a way to isolate these fish to treat them.

  1. Remove the fish from the main pond, into the isolation pond or aquariums making sure that the water you are using in the isolation quarters is the same temperature as the pond water.
  2. Slowly heat the water up to 86°F (no more than 2°F per hour).  If your water is very cool, due this over a two day period.
  3. Leave the fish in the heated water for a 7 day period.  Do not feed the fish during this time as they will be stressed out, and the last thing you want is to have an ammonia or nitrite problem in the water.
  4. After the 7 day heat treatment is finished, slowly cool the water down to 80°F.  Once you reach this temperature, start an antibiotic treatment with various antibiotic products, and Forma-Green in the water…if the fish are still eating.  If the fish will not eat, use probiotic products.  The infected fish will need to be kept on these antibiotics for a two week minimum treatment.  You may continue these treatments for an extra week if the fish are not quite healed up yet.