Common Koi Health Issues

Clean, well-aerated water and a healthy diet can be helpful in minimizing the likelihood of health issues in koi fish. However, in the event that your koi become afflicted, part of any enthusiast’s role is recognizing some common koi health issues. Be it parasitic, bacterial, fungal or viral, there are over 100 recognized koi afflictions. Here is a look at a few of the more common ones and how you can recognize them.

Ichthyophthirius Multifiliis

More commonly known as Ich or White Spot, this is a parasite (more specifically, a ciliated protozoan) that is perhaps the most common koi illness. The parasite manifests itself as white spots that look like grains of salt. The parasites feed off the koi’s body cells before falling to the bottom and reproducing in cysts.

It is particularly fatal to smaller fish.

Ulcer disease

Ulcer disease or simply “ulcers” are caused by the bacteria Aeromonas Salmonicida.  The word “disease” is a bit of a misnomer, as ulcers are the result of a bacterial infection.

Aeromonas is ubiquitous in aquatic life. It is always found in water, and always found on koi and other freshwater fish. Under normal, healthy conditions, Aeromonas will have no ill effect on koi.  However, when fish are highly stressed, or their immune systems are otherwise weakened, the bacteria are allowed to take hold and start causing damage. Ulcers will appear first as red spots on the body, which will soon precipitate into open wounds if left untreated.

Anchor Worms and Fish Lice

If your koi are flashing or rubbing, Lernea Elegans (the Anchor Worm) might be the culprit. Visible to the naked eye, it is a thin crustacean parasite that attaches ventrally for a two-week period before reproducing.

Another plainly visible crustacean parasite, Argulus (known as Fish Lice), will attach with hooks to your koi. As a result of the wounds that their blood sucking causes as well as the bacteria present in them, both parasites will often precipitate a secondary bacterial infection (ordinarily ulcer disease).

Carp Pox

Viral in nature, this particular affliction is not fatal. Waxy, opaque lesions or blister spots that disfigure the koi’s appearance denote its presence. The lesions should not be removed and it is believed that heat and higher salinity can help the lesions to heal naturally.

Flukes

Gill (Dactylogyrus) and skin (gyrodactylus) flukes are microscopic worms. Given the right environment to thrive in, they can destroy gills and deplete protective mucosal coating respectively leading to bacterial infections. They are also bacteria vectors through direct contact. Flashing and rubbing are signs that your koi could have flukes.

Flukes can be responsible for the loss of a significant amount of fry.

Dropsy

Bulging eyes and scales are all signs that your fish might have dropsy or pinecone disease. Bacteria—either as a primary or secondary infection (from a prior infection or injury)—and water temperatures are often to blame.

A compromised osmoregulatory system will lead to diminished kidney function and an inability for proper water expulsion. It will result in renal failure if not treated. It has a high mortality rate, but it is treatable.

Some things to consider in helping to prevent illness or health issues:

• Water temperature is a contributing factor for health in both the cold-blooded fish as well as those pathogens that live in it. As a general rule, many pathogens struggle to survive at higher temperatures. Additionally, a koi’s immune system operates at a more optimal level in higher temperature waters.
• The same applies for salt. Generally, higher salinity will help against freshwater parasites as well as aid the osmoregulatory system and act as a calmative agent for fish already under stress.
• However, the treatment protocols in terms of medication, isolation and salinity level increases vary slightly from enthusiast to enthusiast and merits an article all to itself.

At Next Day Koi, we source our fish from some of the biggest and best koi farms in the world. All of our koi are quarantined for a minimum of two weeks before being listed for sale and are monitored closely for any signs of health problems during that time. If any health problems become apparent during quarantine, the affected koi are treated accordingly.