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).
Treatment options
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.