Koi Diseases

Guide to Koi Diseases

A Koi's health depends upon the environment provided by the human owner. Koi have a high resistance normally and succumb to disease usually only after exposure to stressful conditions that break down the normal immune system. A stressed fish becomes a sick fish. It has been said that:

Fish Disease = Stress Condition + Disease Agent

Stress is the main factor man has the most control over. Many disease causing organisms normally occur in the same environment as the fish. They usually only become a problem when present in significant quantities and/or stress occurs. Therefore, by controlling stress you can help maintain a healthy pond. Prevention is easier than treating your pond for disease.

Some causes of stress are:

Disease Agents:

1. Bacterial

  • Flexibacter Columnaris (fin & tail rot).
  • Aeromonas (hole-in-the-side).
  • Pseudomonas.
  • Vibrio

One of the principal causes of fish mortality is bacterial disease. Except for "columaris" nearly all bacterial infections occur secondarily to some other primary stress. Most are gram-negative organisms. Treatment: acriflavin, nitrofurans, oxytetracycline, kanamycin, chloramphenicol, sulfanomides, salt, etc. as a dip, topical, injection, or in feed.

2. Viral

I know of no effective treatment except to remove nodular growths by scraping.

3. Fungal

A secondary infection at the site of some other fish injury. Also affects damaged or disturbed fish eggs. Treatment: acriflavin, iodine, malachite green, methylene blue, salt, formalin as a bath, topical, or in pond.

4. Parasitic

  • Lernaea (anchor worm)
  • Argulus (fish lice)
  • Monogenetic Flukes
  • Ich
  • Trichophyra
  • Internal parasites

Most fish carry some parasites, but develop a degree of resistance that prevents problems. On the other hand, parasites such as anchor worms and fish lice usually are a problem whenever present. Young fish are more susceptible to illness caused by parasites. Stress situations and/or seasonal climatic variations may bring on infection. Some parasitic infections can be mistaken for bacterial diseases or viral infections and some may cause tumors. Treatment: Dylox, Masoten, Demilin, Formalin, Malachite Green, potassium permanganate or salt in the whole pond or in a bath.

Treating fish diseases is sometimes a haphazard affair because we do not always exactly know what the fish is suffering from. It is not easy to make a correct diagnosis and then, from that "guess," choose a medication and dosage. Treatments for Koi diseases are still relatively unsophisticated. There are no funds available in the U.S. for the development of ornamental fish medicine.

Note: Dead fish decompose very rapidly and generally are of little diagnostic use even if they have been frozen. It is better to have someone examine a live, diseased fish. Fish cannot be examined over the telephone!

Methods of chemical treatment, (listed from most conservative to most drastic):

  • External swabbing
  • Dip (five minutes in separate bath, aquarium)
  • Bath (30 to 60 minutes)
  • Sick tank or whole pond (low concentration for 12 or more hours)
  • Feed
  • Injection

Whole pond treatment advantages include apparent ease of administration and a desire to destroy all the harmful pathogens. The disadvantages are that biological filtration may be severely affected and drugs used in the treatment tend to be absorbed by organic debris in the pond. In addition, therapeutic drug levels may not be reached as pond drug dosages are usually lower.

External swabbing with antibiotics and/or disinfectants can be surprisingly effective. The disadvantage is that the fish is exposed to handling and possibly anesthetics.

Medication should be attempted after water quality and stress conditions have been improved. Partial water changes are very effective in improving water quality and relieving stress.

Beware of the problem of disease organisms that may be resistant to a particular drug. Maintain a current listing of drugs that are effective. Acriflavin, for example, is frequently used for shipping and handling of fish, and has been abused to the point that strains resistant to this drug are not uncommon.

Suggestions for a Koi first aid kit:

  • pH test kit
  • Ammonia test kit
  • Chlorine/chloramine test kit
  • De-chlor
  • Dylox or Demilin
  • Malachite green and/or methylene blue (note: methylene blue can kill your bio-filter)
  • Rock salt ("Synergistic" some medicines are more effective when combined with salt treatment)
  • Nitrofuran powder or ointment
  • Panalog ointment
  • Formalin.
  • "Handbook on Drugs and Chemicals Used in the Treatment of Fish Diseases" by Nelson Herwig.*
  • "Koi Health and Disease" by Erik Johnson D.V.M. or "The Manual of Fish Health" from Tetra Press.

* Herwig Nelson: Handbook of Drugs and Chemicals Used in the Treatment of Fish Diseases. Springfield, Illinois. Charles C.Thomas, Publisher.

For more information: Dr. Erik Johnson's Web Page.

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