The virus often occurs despite the best fish keeping conditions and is highly infectious. It only infects koi in the garden pond and it infests the animals in water temperatures between 10 and 30 degrees. The fish stay near the water surface and they look like they are gasping for air. The affected animals’ eyes appear sunken and dull. There is nothing obviously noticable externally, only on closer look do you notice the changes in the mucous membrane and an extreme fading of the gills, which are decaying slowly. This symptom is called necrosis. Unfortunately the animals die within a few days because there is no really effective method of treatment at present. Animals which survive this disease are carriers of the virus and infectious all their lives.