Carp Pox is the most common virus in the koi world. It is also called temperature stress because this virus can only give a skin reaction when the temperature changes. It is also one of the oldest common signs of disease in carp (for over 400 years). This picture is caused by a DNA virus from the Herpes group. In the Netherlands, it has not yet been possible to isolate the virus. The symptoms appear when the water temperature is low. Usually, these symptoms disappear when the temperature rises and is high over a longer period of time. It is striking, however, that the symptoms appear if the fish ends up in a situation that is far from ideal or if there is a lot of stress.
Usually, the symptoms start on the fins: Pink to white-gray bumps that vary in size from a few millimeters to a few centimeters. The bumps can spread all over the body. They disappear again when the temperature is low for a long time and when the environmental factors are optimal. In consumption carp, it has been noticed that during the presence of these bumps, the bones are soft (osteomalacia). The fish will not die from this.
Proper treatment is not possible. This virus is contagious but will not always spread. So there is a good chance that almost all koi already carry this virus. Since this statue is not very popular, one can choose to have the bumps removed. However, this is a beauty operation and since the fish carry the virus, it remains to be seen whether such an operation is useful.
Initially one can try to increase the temperature for a longer period of time. If this does not help, one can try to restore the environmental factors and bring peace to the pond.