Quick referenceCarp pox is a viral skin disease causing waxy white-grey growths on koi + goldfish. Generally non-lethal; growths regress in warm summer water and recur in cool seasons.
Symptoms
White/grey waxy patches
Tumor-like lump
Patches on fins + body
No behavioral change
Cause
Cyprinid herpesvirus 1 (CyHV-1). Latent infection that flares in cool water (under 65°F) + recedes in summer warmth. Common in mass-bred koi.
Treatment options
No treatment needed. Carp pox is mostly cosmetic. Growths regress at 75°F+. Most pond keepers do nothing.
Warm water. Move fish to indoor system at 75°F for 4-6 weeks. Growths typically fade.
Improve nutrition. High-quality protein + vitamin C in diet supports immune response.
Surgical removal. Only for valuable show koi with disfiguring growths. Veterinary procedure under MS-222 anesthesia.
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
Buy koi from CyHV-1-clean breeders. Maintain warm water (above 70°F) for sensitive show koi.
Fatality + outcome
Almost never lethal. Cosmetic; reduces show value.