Solutions for Sick Koi Fish

Koi are colorful, beautiful and fascinating to watch, but treating them when they're sick can be tricky. The best way to ensure your koi remain healthy and happy is to maintain the pond. Keep it clean and fresh, with a proper briny mixture. and watch your fish for signs of injury. Most infectious fish diseases are opportunistic and strike through open wounds, sores or areas of the fish body where the slime coating is lost.

  1. Bacterial Infections

    • Koi can contract an infection if they are injured or areas of the slime coat have been stripped away. Visible signs of infection are cotton-like growths, discolored areas or bulges.

      If a koi shows signs of a bacterial infection, such as Aeromonas hydrophilia, move it to a warm isolation tank immediately. Warm water will facilitate healing by boosting the immune system. A couple of medications are available for treatment. Tricide-Neo creates holes in the bacterial cell walls, allowing antibiotics to enter. Vet-administered injections are also an option. A veterinarian will take samples to determine a course of treatment targeted to destroy specific types of bacterial infections.

    Parasites

    • Argulus, or fish lice, is a common koi parasite with a crustacean exoskeleton. It attaches to the skin of a koi, pokes a hole with its sharp proboscis, and feeds on the blood. Argulus lays eggs on solid surfaces like rocks. The gestation period of argulus eggs is about a month, and the hatchlings are so tiny they can't be seen by the naked eye for about six weeks, during which time they will attack every living thing in the pond. Regular treatment with a homeopathic parasite cleanse will help rid your pond of these pests, along with dedicated rock cleaning.

      Another common parasite is Lernea, or anchor worms. These are easy to spot. They resemble black strings that attach to the side of koi. They are fairly easy to remove with a pair of tweezers as long as you disinfect the fish skin with potassium permanganate or iodine. Look for these pesky worms in the summer.

      Treating parasites promptly is vital to the health of the koi. While the effect of the parasite itself is minimal, they damage the fish skin and slime coat, making the koi vulnerable to disease.

    Koi Herpes Virus

    • Koi Herpes Virus (KHV) is one of the deadliest diseases to koi, and can kill an entire pond within a week. Symptoms include gill necrosis, gasping at the surface, fatigue, abnormal mucus secretion, sunken eyes and patches of pale skin. If a koi exhibits these symptoms, remove it from the pond, raise the pond's temperature to 86° F, and get the sick fish to a vet for testing. The best prevention for this disease is to quarantine new fish for at least three weeks in an isolation tank maintained at 75° F before releasing into the pond.