It is every Koi fish owner’s nightmare. You wake up one morning to find a pond full of sick fish! You don’t really know what they have, but you know that something is wrong. Below you will find a list of some of the most common complaints from Koi fish owners, and some ideas as to what the problem might be. Before doing anything, you will want to do your homework and research the best treatments for your fish.

Here are some things that should alert you to a problem:

  • Sudden death – this is obvious but if only one fish dies, the rest of the pond could still be affected. Possible problem: poisoning and/or severe bacterial problem.
  • Lethargic fish – they won’t eat and may hang around on the surface of the water or stay at the very bottom of the pond. Possible problem: poisoning and/or severe bacterial problems.
  • Your koi fish may try to leap out of the water. Possible problem: water imbalance or parasites.
  • Fish rubbing against rocks and other solid objects in the pond. You may notice silver coloring on the sides of their bodies where they rub their scales off. Possible problem: water imbalance or parasites.
  • Heavy breathing, gasping motions. They may also crowd around the water inlets. Possible problem: low oxygen levels, water imbalance, parasites, anemia, or gill disease.
  • Cloudy or grey areas on their skin. Possible problems: could be a variety of diseases, parasites, bacterial infection, and water imbalance.
  • Skittish and/or shy behavior. Ragged fins. Possible problem: poor water quality, polluted water, parasites, bacterial disease.
  • Covered in slime. Could also have skin lesions or ulcers. May also show reddening or inflammation on the body and fins. Swelling may also occur. Possible problem: physical injury to the fish, parasites, bacterial disease, poor water quality or pollution.
  • Pop-eye – a bulging eye. Possible problem: viral infection, bacterial infection, tumor, heart or kidney disease, parasites, genetic disorder
  • Tiny white spots on the skin of the fish – looks like they are sprinkled with salt. Possible problem: Ichthyophthirius (Ick)
  • Cotton-like patches on the skin. Possible problem: fungal infection, cotton wool disease, bacterial infection.
  • Cloudy eyes. Possible problem: physical damage, poor nutrition, poor water quality, bacterial infection.

Many of these problems will come in clusters, which makes it increasingly difficult to diagnose your koi. And remember, even if none of the other fish in the pond are exhibiting signs of illness you will want to treat the entire pond. Quarantine the ones that are showing symptoms and keep a close eye on the rest of the pond. If the outbreak is bad enough, you may have to drain your pond and start from scratch.

Originally posted 2015-11-22 07:49:58.