Our complete line of Koi Diseases

Anchor Worm

Crustacean parasite, Lernaea - Anchor worm is a common parasite on our Koi which is clearly visible to the naked eye and can reach 10 to 12mm. The parasite burrows its head into the Koi's tissue, under...(click on product image for more details)


Costia is a minute Flagellate with 3-4 flagella. It affects both the skin and gills of Koi, and reproduces itself by binary fission. Infestations of this parasite can appear very rapidly indeed, and Koi...(click on product image for more details)

Cotton Wool Disease

Columnaris (Flexibacter columnaris) or Cotton Wool Disease is another bacterial infection. The common name comes from the white tufts that develop around the mouth and spread to the body and fins, often...(click on product image for more details)


Raised scales rather like a pine cone and eyes standing out from the head. Dropsy itself is not a disease, but rather a result of some other cause. Dropsy is a term given to the swelling that occurs...(click on product image for more details)

Finrot and Ulcers

A number of bacteria are associated with finrot, lesions and internal hemorrhaging, notably Aeromonas and Pseudomonas. Ulcers usually start at the site of an injury, the bacteria then infect it causing...(click on product image for more details)

Fish Lice -Argulus

Argulus another crustacean parasite, round and up to 1cm wide. They have a sucker to hold on to the Koi with needle-like mouth parts which they stick into the Koi and inject a toxin. This causes intense...(click on product image for more details)

Gill Maggots

Gill maggots are the mature females of the parasitic crustacean Ergasilus. Ergasilus gill maggots will appear as grayish black and white parasites several millimeters long infesting the...(click on product image for more details)

Saprolegnia Fungus

One of the most common fungal infections of Koi. The fungal spores will grow anywhere on the Koi, including the gills, initially germinating on dead tissue. Their threadlike hyphae release digestive...(click on product image for more details)

Skin and Gill Flukes

Gill and Skin flukes are two of the family of monogenetic trematode genera, all of which are characterised by the large grappling hooks which are used to attach themselves to their victims. Flukes...(click on product image for more details)


Trichodina is one of the easiest protozoan parasites to detect under the microscope as it is almost perfectly round with hundreds of hooks which resemble cilia found its periphery and it constantly...(click on product image for more details)

White Spot -Ich

Caused by Ichthyopthirius multifiliis. The white spots on the skin, gills and fins are individual protozoan cells that are under the skin and feed on the body fluids and cells. They then punch out of...(click on product image for more details)

Koi Diseases

Virus, Bacteria, Fungus and Parasites cause koi ailments

Without question the best, the most effective and the least expensive approach to dealing with Koi diseases is to prevent them. A proactive approach is far better than a reactive one. The Koi environment , even when things are as near to perfect as we can get them, is a hostile one. But, on the other hand, the koi environment is perfect for all kinds of diseases to proliferate. Koi live with a wide array of pathogenic bacteria and parasites. Most of them are opportunistic by nature and easily dealt with by the koi's immune system, assuming it is fully functional. If it is not they will overrun the koi and prevail, resulting in problems and certainly life threatening complications. But, regardless of why, sooner or later, most of us will have to deal with koi diseases at some point. There are many resources that are available to assist you with dealing with koi diseases; one of my favorites is The Koi Doctor.

It is important that when this does happen that you are able to identify the koi disease and know how to treat it. Koi by nature often harbor a low level of disease that is effectively controlled by the koi's immune system. However when the koi becomes stressed it becomes susceptible to attack from pathogens (viruses, bacteria, fungi & parasites). It is imperative that you treat the symptoms promptly and accurately and endeavor to remove the initial cause of the disease.

Koi disease and treatment involves

Chemical treatments or medications are used to kill off the pathogen. However many chemical treatments can damage the pond plant life, poison the koi and also retard beneficial bacteria growth if they are used incorrectly. Unlike humans who take the medication orally, koi disease and treatment takes a different route. It is the actual water that is treated. It is imperative to know the pond volume so as to not over or under dose. This method of koi disease treatment is ideal because many fish can be treated at once. Unfortunately certain pathogens have become immune to antibiotics and insecticides. Dosing the pond will overcome the vast majority of pathogens but from time to time it may be necessary to treat the individual koi with antibiotic injections. Under these circumstances you need to know the weight of the koi, so as to prevent a lethal overdose.

Pathogen type 1 - Viruses

Viruses are extremely dangerous and difficult, or impossible, to deal with in a pond. Medication will not remove a virus from the koi. The only cure is the koi's own immune system. Viral infections have been known in both the USA and Europe to be responsible for the closure of certain breeding farms. As with humans, in particular children, it is possible to immunize against certain viruses by vaccination. This process causes a very mild form of the virus to take effect, which in turn causes the koi's immune system (white blood cells) to fight the attack and build up antibodies. Unfortunately this type of treatment is not really available at this time.

Pathogen Type 2 - Bacteria

Fin rot, gill rot, ulcers and mouth fungus are common forms of bacterial attack. Treatment of this type of pathogen normally takes the form of the addition of chemical treatments to the pond water. Ulcers (Aeromonas) and fin rot (Pseudomonas) are the two most common types of bacteria affecting koi carp. Dropsy, another common bacterial infection is best treated using a course of antibiotics, administered by a vet in the form of injection or food.

Pathogen Type 3 - Fungus

Fungal infections can be difficult to treat, particularly in advanced cases. Koi affected by fungus will have the characteristic cotton wool type growths found on wounds, cuts and abrasions. Fungal infections unlike other koi disease isn't contagious and won't infect other koi or goldfish living in the pond. The most common type of fungus is Saprolegnia and will infect both koi and other pond fish. Treatment for fungal koi disease involves using malachite green, administered to the pond water. In stubborn cases it may be necessary to bath individual koi with Pond Salt to retard the fungus.

Pathogen Type 4 - Parasites

Parasites fall into different categories. There are single celled parasites (protozoa) that are relatively easy to treat using formalin and malachite green. Examples include Trichodina, Whitespot, Ichthyobodo (Costia) and Chilodinella. These single celled protozoa attach themselves to the koi's skin and feed on skin and mucus, causing great irritation to the koi. Larger parasites, consisting of many cells (metazoa) include gill and skin flukes, fish lice, anchor worm, tapeworm and leeches. This koi disease and treatment involves using salt baths and in some cases malachite green, although this doesn't always work due to the high concentrations required.

How to identify koi ailments and koi disease.

In some cases it is possible to see the disease causing pathogen visually, e.g., fungal infections with their cotton wool like symptomatic growths. However in a lot of cases this is not possible and you will need to get a mucus sample and place it under a microscope. It is a good idea to get mucus samples from healthy koi, therefore allowing you to make accurate comparisons between what is and isn't the norm.