Koi Eye Diseases

Koi parasites and diseases are present in most koi ponds, but a disease episode is usually triggered by some type of stressor. Poor water conditions, rough handling, poor nutrition or harassment by a predator can cause an outbreak of illness among the fish. Determine the cause of stress so you can take care of it after treating their illness. It's important to quarantine new fish before introducing them into an established group to avoid the possibility of spreading disease. Some bacterial infections will spread quickly in a koi pond, and fish should be separated from the others until symptoms are gone. Sick fish should be isolated in a quarantine tank for treatment. In an ideal situation, each diseased koi has an individual quarantine tank. Koi require very good water conditions and adequate nutrition while being treated.

  1. Cloudy Eye

    • Koi need good water conditions and regular nutrition.

      Cloudy Eye is usually due to a gram negative bacterial infection. It is similar to a disorder in which a translucent film appears over the entire eye. Sometimes just the iris, the colored portion of the eye, becomes cloudy from an infection caused by one of the gram negative bacteria. Redness and swelling may develop around the eye. Parasites or flukes that attack a Koi's eye cause a cloudy, opaque film to form over the entire orbit.

    Pop Eye

    • Changes in the water can stress koi.

      Pop Eye is a progressive bacterial infection caused by Aeromonas hydrophilia or Pseudomonas bacteria. It may develop into Dropsy or Pine-Cone Disease in which the fish builds up fluid in his body and around his eyes, causing them to bulge. As disease advances, the fish's scales stick out until it resembles a pine cone. This disease has occurred when Koi were moved from acidic to very alkaline water. The symptoms become more severe and, without treatment, Hole-in-Body Disease develops. Shallow raw areas become deep ulcerations, holes, on the fish's body.

    Spring Viremia

    • Koi should be quaranteed at first sign of disease.

      Spring Viremia recently appeared in the U.S. and it's very contagious and difficult to diagnose. Infected fish have noticeable, dark, swollen pop-eyes and bloated abdomens. They are lethargic, swim erratically and require vigorous treatment.

    Koi Herpes Virus (KHV)

    • Koi can get an eye injury in the pond.

      The mortality rate for this deadly disease is 90% and is very contagious. Once a disease of carp, KHV has appeared in Koi and can wipe out entire ponds. Sick fish are lethargic, develop bleeding gills, white blotches on their skin and gills and their eyes look shrunken deep in their heads.

    Saprolingiasis and Protozoan Infection

    • A Koi pond must be maintained for good fish health.

      Saprolingiasis is a fungal disease, caused by the saprolignia fungus. It's characterized by small white cotton-like patches on the skin and over the eye surface. If eye is attacked by a protozoa, a clear or transparent film forms over it. Gradually, translucent spots develop on other parts of the Koi's body, which helps diagnose the ailment.

    Eye Injury

    • Koi Herpes is very contagious among fish.

      If the entire eye seems ready to "fall out" the fish may have been injured in a fight or bumped a pond plant. There's swelling and redness around outer edges of the entire eye. It should be treated to avoid development of secondary bacterial infections.