Koi Health » Parasitic Koi Diseases

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 a scale and only the body and tail are normally visible.

The juvenile stages settle in the gills of Koi, when they mature they mate and the male leaves the Koi, the fertilized 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.

Lernaea lay eggs which can lay undetected in the pond and can hatch when conditions and water temperatures are right.

Treatment is by manual removal of the parasite with tweezers under anesthetic, ensuring that the whole parasite is removed. To be sure of complete removal, dip a cotton bud in strong potassium permanganate solution and dab the worm with this solution whereupon it will release its grip immediately. Pond treatments include Dimilin or Paradex.

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 suffering infestations exhibit the classic symptoms of lethargy, clamped fins, rubbing and flashing and the skin can take on a grey white opaqueness.

Costia normally only affects fish that have already been debilitated by some other cause, and can often be seen on Koi as a secondary parasite.

Costia is one of the many fish diseases that are caused by protozoa. It is a somewhat rare disease that is relatively easy to cure if your fish becomes infected by it. There are several treatments for this disease but it is of course preferable to prevent the protozoa from ever infecting you fish by keeping you aquarium clean and your fish healthy and well fed, while at the same time doing what is possible to avoid introducing diseases and parasites into the pond.

A high magnification must be used to view these parasites (300 x) and staining is recommended for positive identification.

Recommended treatments include Potassium Permanganate, Acriflavine and strong salt baths of 3% ( 4 and one half oz. per gallon )

Argulus or fish lice as they are commonly called are a very major threat to your fish’s health. They can cause significant morbidity and mortality when heavily infesting your fish and they have been known to be the vehicle for other fish diseases. Argulus are a crustacean parasite in the subphylum Crustacea, which groups them together with prawns, shrimp, water fleas and others. The animals that are in the Crustacea group have semi-rigid to rigid chitin exoskeleton. The chitin exoskeleton will molt, or shed, as they get larger. Argulus are in the Branchiura class, which is group of Crustaceans that all have similar features. All of the Branchiura are fish parasites.

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 irritation to the Koi and they scratch and jump and can cause bacterial infection.

Argulus have a direct life cycle using only the fish as hosts. They prey upon freshwater fish and marine fish. Argulus can spend a large amount of time swimming around and mating occurs when the male and female Argulus are swimming. The eggs clusters are dropped on any convenient submerged item. After hatching the Argulus makes several metamorphic changes as it goes towards adulthood. The whole cycle takes between 30-100 days depending on the temperature. After hatching they must find a host within a around 4 days or they will not survive.

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.

Ergasilus (gill maggots) will appear as grayish black and white parasites several millimeters long infesting the gills.

Heavy infestations can cause severe damage, eroding the gill filaments and allowing secondary infections to develop.

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 are another common parasite affecting our koi are both egg layers and live bearers. They range from 0.05 to 3.00mm long and there are actually a huge number of species in the genus.

Affected Koi often exhibit classic signs of irritation and flash, jump or rub themselves against objects in the pond in an attempt to rid themselves of their attackers.

Flukes are not visible with the naked eye. When viewed under a microscope, the parasites are clearly visible as nearly transparent and worm like, and the hooks are clearly visible.

Flukes are a bit like fleas on dogs and cats and it is common to see one or two on a slide as a healthy Koi can control parasite numbers and their mucus helps prevent the parasite moving. Treatment is therefore only necessary if flukes are seen in numbers.

Chemical control of both types of fluke can be achieved with Chloramine T, Malachite Green, Formalin, or Potassium Permanganate. In order to kill all generations, repeat treatments may be necessary, the frequency being dependent on temperature and chemical used.

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 rotates as it moves through the mucus, causing tissues damage.

It attacks both skin and gill tissues of our Koi, and can often cause more damage to gills than realized.

Classed as a warm water parasite, it can survive for some time without a host. It causes vegetation of the skin giving rise to a grey white opaque appearance on the body of infected Koi which exhibit the classic symptoms of flashing, rubbing and lethargy.

A magnification of 100 to 200 x is required to view this parasite.

Recommended treatments are Potassium Permanganate.

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 re-invest 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.

Ich is caused by a ciliated protozoan of the genus Ichthyophthirius – Ich is simply an abbreviation of the word Ichthyophthirius. Some people prefer to spell it Ick, perhaps because they find the disease icky? Ich is also known as White Spot Disease since it causes small cysts to form on the skin of infected fish. If you look at the protozoan under a microscope, you will see a round rolling mass with a u-shaped nucleus. This parasite is completely surrounded by cilia.

The Ich parasite starts its life as a free swimming organism that moves around in the aquarium, looking for a suitable host. When it finds a fish, it will attach itself to the outer layer of the fish's skin and start feeing on its bodily fluids. It can also attach itself to the gills, thus making it hard for the fish to breathe. Soon, the parasite will have developed a protective outer shell, a so called cyst, and it is this shell that we can see as a small white grain on the skin of infected fish. A fish heavily infested with Ich parasites can look as if someone had sprinkled it with grains.