Quick referenceKoi herpesvirus (KHV) is a lethal viral infection of koi + common carp. No cure. 80-100% mortality once symptoms appear; isolation + biosecurity are the only defenses.
Symptoms
Color fade
Refusing food
Lethargy
Surface gasping
Mucus on gills
Bulging eye(s)
Sunken eyes
Notched fins
Cause
Cyprinid herpesvirus 3 (CyHV-3). Highly contagious between koi + common carp. Transmits via water, infected fish, contaminated nets/tools/hands. Triggered by water temperatures of 64-77°F (18-25°C).
How is Koi herpesvirus treated?
No cure exists. KHV has no antiviral treatment. Fish that survive carry the virus for life and shed it intermittently.
Heat shock (controversial). Some breeders attempt 86°F heat for 30 days. Limited success. Pathogen-shedding survivors are still carriers.
Cull + sterilize. Most pond keepers euthanize the entire stock + sterilize the system. Drain pond, bleach 10% all surfaces, dry 4-6 weeks before restocking.
Quarantine all survivors. If keeping survivors: permanent quarantine. Never mix with KHV-naive fish.
Always treat in a separate quarantine or hospital tank. Most medications are toxic to coral, invertebrates, and live rock biology. Consult an aquatic veterinarian for valuable fish.
Prevention
Quarantine new koi 60+ days at 75°F to express virus. Never share nets/tools between ponds. Avoid wild-caught carp + Israeli/Asian-imported koi without health certificates. Buy from KHV-tested breeders only.
Fatality + outcome
Catastrophic - 80-100% mortality once symptoms appear. Tank-killer.