This is a very brief guide to some common koi diseases; it is in no way a substitute for a good book on the subject or professional help.

 

For a more detailed guide have a look at the koi health sites listed on our links section.

 

Unless specifically stated most of these problems can be treated using commercial remedies, which state what they are for on the packaging, ask dealer for advice if you don't know which one to buy.

 

Sliminess of the skin.

A grayish white film of excess mucus on the body. This is a reaction to protozoan parasites, notably Ichthyobodo, Trichodina and Chilodonella. Other symptoms of infection by these parasites are scratching and leaping followed by lethargy and failure to eat. Further risks are secondary bacterial and fungal infections of wounds caused by scratching. The parasites are particularly active in spring when koi are still recovering from winter.

 

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 the skin and fall to the bottom of the pond, collect together and begin breeding, the offspring then reinfest the fish. As well as white spots symptoms are scratching and swimming into the water inlet, failure to feed and lethargy. It is fatal if untreated. Fortunately commercial white spot remedies are widely available.

 

Anchor worm.

Crustacean parasite, Lernaea . The juvenile stages settle in the gills of koi, when they mature they mate and the male leaves the koi, the fertilised female settles on the body of the koi and continues to grow, becoming the familiar worm shape. The female buries into the skin and underlying tissue to hold on. The damage caused can become a target for bacterial or fungal infection, which can spread.

 

Fish lice.

Argulus another crustacean parasite, round and up to 1cm wide. They have a sucker to hold on to the koi with needlelike mouthparts which they stick into the koi and inject a toxin. This causes intense irritation to the koi and they scratch and jump and can cause bacterial infection. If they infect the gills they cause severe damage and often death. Most antiparasite remedies will not kill fish lice, a strong chemical is needed which is not freely on sale. Ask a professional dealer or vet.

 

Gill maggots.

Are the mature females of the parasitic crustacean Ergasilus. Heavy infestations can cause severe damage, eroding the gill filaments and allowing secondary infections to develop.

 

Skin and gill flukes.

These are the fish equivalent of fleas. They are two different types of flukes, but despite of their names both can be found on the body and the gills, feeding on mucus. They use hooks to hold onto the koi, this causes irritation and in a weak, sick or stressed koi can become a problem.

 

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 juices, which break down the tissue so the fungus can absorb it, as the fungus grows these juices start breaking down living tissue. Fungus on the body appears as cotton wool like growths, it is hard to tell if a koi has it in the gills, but if it hangs at the surface gulping for air it is likely.

 

Carp pox.

A virus that produces solid waxy lumps on koi. It will not kill koi and is generally harmless, but can look unsightly. It is most often present in small koi and in cold weather, clearing up disappearing when koi grow and in the spring when water temperatures rise.

 

Finrot and ulcers.

A number of bacteria are associated with finrot, lesions and internal haemorrhaging, notably Aeromonas and Pseudomonas. Ulcers usually start at the site of an injury, the bacteria then infect it causing further damage, and fungal infection can also occur. Such holes result in osmoregulatory problems, leading to damaged kidneys and death if not treated. It is worth adding a weak salt solution to the pond as well as anti bacterial remedy, a concentration of 3gm per litre will help to restore the osmotic balance and reduce strain on the kidneys (make sure that the salt is fully dissolved before you add it to the pond). Finrot is easily noticeable, the fins and/or tail look chewed and are red at the edges. Secondary bacterial and fungal infections can develop.

 

Cotton wool disease.

Another bacterial infection. The common name comes from the white tufts that develop around the mouth and spread to the body and fins, often leading to ulcers and a thin appearance. Flexibacter is the bacterium, which causes this disease. Treatment with anti bacterial medicine is usually effective.

 

Dropsy.

Raised scales (rather like a pine cone) and eyes standing out from the head. A sign of a number of conditions may be congenital heart or kidney failure or an internal bacterial infection. Bacterial dropsy is infectious so treat with an anti bacterial remedy and if possible isolate affected koi.