Vital disease occurs when a virus infects the cells of its host and multiplies rapidly within them. Several viral diseases can affect koi. Some, such as Spring Viremia Carp virus, are extremely contagious and the mortality rate is high. Viruses spread when infected faces are released into the water.
The virus most commonly found in koi is carp pox. It presents itself as easily visible, opaque, waxy looking lumps on the skin. One or more of these may be present anywhere on the body, head or fins. In extreme cases, the body can almost completely cover with them. Carp pox is generally observed in the spring, particularly on young fish.
As the water temperature rises, the lumps can be seen to break up and often completely disappear. No chemical treatments are available for viral diseases; the keeper must rely on the fish’s immune system to combat them which means self cure. The wax like growth of carp pox can be clearly seen. Although it looks unsightly, it generally disappears as water temperatures rises.
Regularly disinfect handling equipment. As koi fish age, they developed an immunity to carp pox. It is a good idea to become familiar with using a microscope so that you can identify parasites and apply the appropriate treatment. Some of the more common parasites will be discussed later.
Koi are voracious feeders, but offering them more than they can eat in a reasonable time is wasteful. Unless skimmers are turned off at feeding time, many pellets will be removed from the pond surface before they can be eaten.