Informational slides on many common koi diseases and their treatments.

1. Koi Diseases and
Their Treatmentsby
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When it comes to the maintenance of
your koi pond, probably the most
common task you’ll spend time on is
disease prevention and treating
diseases that do arise.

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The more you know about koi maladies,
the better you can treat them.
BELOW ARE SOME OF THE MORE
COMMON KOI DISEASES AND THEIR
TREATMENTS.

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1. ICH
One of the most common diseases found in Koi is Ich
(aka; White Spot disease). It is a protozoan that begins
its growth in the pond and later attaches to the gills of
the Koi as it matures.
TREATMENT:
For short treatments in quarantine, one could do a
quantity of 1.5 mg of malachite green for every liter of
water for up to 1 hour (or 6mg of malachite green for
every gallon of water). Always wear gloves when
handling both malachite green and formalin.

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2. DROPSY (PINECONE DISEASE)
Fish that have dropsy often show signs of
swelling or lifting of the scales. Their eyes will
frequently bulge. If you ever notice this, don’t
hesitate to separate the infected fish from the
others.
TREATMENT:
Dropsy is, more or less, terminal. By the time
you see your fish bloated with standing scales it
means that there is kidney and liver failure.
Prevention of infection to your other fish is
recommended with Medi Koi or Debride RX.

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3. TAIL ROT
Tail rot and fin rot are really secondary to the original
problem which could be stress or poor water quality
that is causing your koi to be immuno-compromised
in the first place.
TREATMENT:
One good start to treating this malady is by a 30 -
50% water change of your pond. Using Mela-Fix is
also a great option for dealing with the bacteria
themselves and you can also add salt to your pond
which will go to work on your bacteria and also lower
stress levels for your koi.

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4. MOUTH ROT
Mouth rot is a symptom of something larger and
that is usually poor water quality that is causing
your fish’s health to be compromised and open
to infection.
TREATMENT:
You’re going to want to stop feeding for the time
being and start improving your water quality by
doing a 30% water change. Next thing would be
a light salt bath treatment and perhaps a
treatment of Mela-Fix.

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5. CHILODONELLA
Some of the symptoms included with this protozoan parasite
are: dying on the surface and rolling over on the fish’s s
sides. This is a notorious killer of koi.
TREATMENT:
You will want to increase the salt concentration in the pond
for 2 weeks as well as increasing aeration.

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6. AEROMONAS
BACTERIA
These bacteria are associated with ulcers and fin
erosion.
TREATMENT:
The koi will need to injections of Chloramphenicol.
This treatment should yield positive results in 3-4
days.

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7.PSEUDOMONAS
BACTERIA
Like its cousin, aeromonas, this bacteria is also
associated with ulcers and fin erosion.
TREATMENT:
Infections of this nature will require an injection of
Baytril.

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8. COLUMNARIS
This bacteria will attack sites of injury but will
cause fin, tail and mouth rot. Additionally fish
can be vulnerable to it during times of stress.
Your fish may develop a white film on their skin
and display sunken in eyes. It can be a rapid
killer so be sure to take swift action.
TREATMENT:
Feeding your koi Medi-Koi or Debride RX will
definitely help your fish with an “inside out”
treatment strategy.

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9. ANCHOR WORM (LERNEA)
Anchor worm, also known as Lernea is a
crustacean parasite that attaches to, and digs
into the skin of fish. The female Lernea attaches
to fish while males do not. The worm feeds on
the fish, damaging its tissue.
TREATMENT:
They can be removed using tweezers or other
small pincers. After removal, rub some
Neosporin on the infected area. Use Dimilin,
Dylox or Lufenuron to treat the pond.

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10. ARGULUS (FISH LICE)
These unwanted invaders have eight legs and
rounded bodies. They also have to big suckers
which are used to attach to the fish. Their
appearance leads to their nickname, “fish lice”.
These parasites can cause considerable irritation
to fish and can lead to bacterial infections.
TREATMENT:
As with anchor worm, treatment will consist of
Dimilin but another product also works as well,
Lufenuron. You should see positive results in a
matter of days.

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11. FUNGUS
Some causes of fish infections, such as fungal
hyphae or spores, require a microscope to see them.
Mild or moderate infections can be treated and
possibly cured if they are caught early. These types of
fungal infections are not typically contagious and
usually only a single Koi becomes infected.
TREATMENT:
Fungus can be removed by gently rubbing the area
with a cotton swab while the infected area must be
treated with an antibiotic or antimicrobial cream
immediately afterwards.

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12. LYMPHOCYSTIS
Your Koi fish may have Lymphocystis if its displaying
any buff discoloration on its skin. Another sign of
Lymphocystis is rough, raised lesions on its skin.
TREATMENT:
You will want to put the infected fish in a quarantine
tank and increase the heat. There is a treatment
containing “neutral acriflavine” that will help defeat
the virus (this product takes the brand name
“Lymphocystis Cure”). It is entirely possible and not
uncommon for the virus to go away on its own.

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13. EPISTYLIS
Epistylis is an uncommon parasitic infection that is
dangerous and can cause other diseases in your Koi.
It is usually caused by poor management of the water,
resulting in dirty water infected with parasites.
TREATMENT:
Change the water in the pond and add salt (0.3%
concentration) to combat these parasites. One can
also put the affected fish in quarantine for 2 weeks
while raising salt levels to 0.3%.

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14. SKINNY DISEASE
The disease is caused by a bacterial infection that causes the
fish to have a sucked-in gill appearance. Its head will often
appear much bigger than the rest of its body.
TREATMENT:
Adding extra food to the fish’s diet can usually clear up this
disease. However, sometimes this doesn’t help and if the
bacterial infection persists, adding erythromycin to the fish’s
food normally clears the infection up quickly.

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15. CARP POX
Your Koi fish may have Lymphocystis if its displaying
any buff discoloration on its skin. Another sign of
Lymphocystis is rough, raised lesions on its skin.
TREATMENT:
There is no effective treatment for this virus but
fortunately it usually goes away on its own. Gradually
heating the water may expedite the virus diminishing.
For some pond owners this is just something that
shows up every winter and spring and goes away with
the onset of summer.

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16. SPRING VIREMIA OF
CARP (SVC)
As the name suggests, this viral disease likes cold
water and shows up in spring when the water is still
cold and your koi’s immune system is not in full
swing. Some of the symptoms that you may see are a
reddening of the skin and swim bladder
inflammation.

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17. HEXAMITA
This disease also known as “hole in the head”
disease is protozoan parasite responsible for lesions
in the dermal layers of koi. You will notice your koi
being lethargic and, more definitively, you will notice
an erosion of the skin (and usually the fins as well).
TREATMENT:
As with many diseases, you will want to quarantine
this fish. You will also want to establish a treatment
course with a product called Flagyl for 10-12 days.

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18. COTTON WOOL DISEASE
Another disease Koi sometimes suffer is called
Columnaris, which is sometimes also called Cotton
Wool Disease. White threads in the fish’s mouth and
a dry skin appearance are the main characteristics of
this disease.
TREATMENT:
You can put potassium permanganate in the water to
help clear up the condition. Additionally, injecting
antibiotics and treating the wound directly will help
care for the disease.

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19. FLUKES
There are two main classes of flukes; 1) gill flukes and 2) skin flukes.
Both kinds are microscopic so if you suspect your fish are suffering from
flukes you will need a microscope to verify it. Dactylogyrus or gill flukes
will attach to the gills and, as the name suggests, body flukes or
gyrodactylus attach to the body.
TREATMENT:
You can quarantine but it is likely that your entire pond is afflicted with
the flukes or their eggs so you can treat with medications like Aqua
Prazzi, potassium permanganate or Fluke Solve (both AquaPrazzi and
Fluke Solve have the same active ingredient; “praziquantel”).

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20. OODINIUM PARASITES
The disease caused by these parasites is sometimes called
Velvet Disease because it resembles a velvety golden dust,
which covers the fish. Other symptoms include ragged fins and
a loss of scales and skin. Though it is somewhat rare there are
treatments.
TREATMENT:
Adding salt to the pond’s water does not normally clear up
Velvet Disease. The best option is to add 37% Formalin to the
water as this has been shown to be most effective.
Alternatively, Simazine can also be used to treat oodinium.

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21. COSTIA
Costia, like Flukes, are a parasite. In this case it is a
microscopic flagellate that can reproduce rapidly. Typically koi
don’t suffer from costia unless they are already compromised in
some way to begin with so it would be classified as a secondary
illness.
TREATMENT:
There are treatment options for costia. Malachite green and
37% formalin can be used but you will need to make sure there
is no salt in the pond to start with. If this treatment is chosen
be sure to increase aeration.

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22. POP EYE
Pop eye is also called exophthalmia and is really not linked to
any one illness but is more of a symptom of something more. It
is a direct response to an excess of fluid or possibly gasses built
up behind the eye which then cause the eye to bulge is distend.
TREATMENT:
The best course of action is to immediately quarantine the fish
and do a light salt bath. You will also want to greatly reduce
feeding and how much you give it. You will also want to do 25%
water changes daily and monitor water quality on a regular
basis.

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23. CLOUDY EYE
Cloudy eye is somewhat uncommon but it can occur. This
malady is typically a symptom of something else going on
rather than something attacking the eye specifically.
TREATMENT:
Treatments for cloudy eye are a medicated koi food formulated
to handle fungal and bacterial issues called Medi-Koi and or
Mela-Fix. Mela-Fix is actually an oil extract from the Melaleuca
tree mostly occurring in Australia and it has natural anti-
bacterial properties.

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24. LEECHES
Unfortunately, leeches aren’t just looking for a free ride but also
a free meal and eventually they will cause mortality of the host
fish if left untreated. Leeches can also transmit the koi disease
known as SVC.
TREATMENT:
Some treatments for leeches include a product called Masoten
which comes in powder form. Another product is called
malathion however many recommend against this treatment as
it is an organophosphate insecticide and though it will kill
leeches it may also harm your koi in the process.

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25. ULCERS
Ulcers on the skin of your fish result from bacterial infections
that form on scales, causing them to become red. The infection
causes holes, or ulcers on the exterior of the fish and will
eventually result in loss of scales if left untreated.
TREATMENT:
Maintain a healthy, clean pond and treat ulcers with a topical
antibacterial such as Panalog to stop the bacteria in their
tracks.

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26. SAPROLEGNIA FUNGUS
One of the most common fungal infections found in Koi fish
comes from the Saprolegnia fungus. Spores from the fungus can
grow on any part of the fish, including its gills. The fungus first
attacks the fish by germinating on dead tissue.
TREATMENT:
The afflicted fish will need to be isolated in a quarantine tank with
the temperature raised to at least 77 degrees F. Additionally, it
will be very beneficial to also get your salt levels up to around
0.3%.

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27. TRICHODINA
One of the easiest protozoan parasites to see under a
microscope, and subsequently confirm your fish is infected, is
Trichodina. An infection of this parasite can be detected by a gray-
white opaque appearance on the body of infected Koi.
TREATMENT:
Treat this disease with a five day course of increased salinity (0.5
to 0.6%). Due to increasing tolerance of some organisms to salt
treatments a course of formalin may be necessary.

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28. KOI HERPES VIRUS (KHV)
This virus is a potent one. Some of the effects of this disease are sloughing off of
the skin which leaves the koi vulnerable to bacterial infection. Your koi will be
lethargic and have sores and lesions on its skin, gills and fins.
TREATMENT:
Increase salt concentration to around 0.45% and bring the water temperature up about 1
degree F every hour until it gets to 87 degrees. The fish should remain in this situation for 4
days during which medicated food such as Medi Koi should be fed.

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29. GILL MAGGOT
Another parasite sometimes infecting Koi is the gill maggot. The
parasite most often attacks the Koi’s gills and has a maggot-like
egg sac appearance. It is a relatively uncommon parasite
sometimes found in Koi ponds but when present, can cause Koi
quite a bit of irritation.
TREATMENT:
The product Lice-Solve has been shown to be effective against gill
maggots (as well as argulus) but you will need to increase
aeration. You can treat the whole pond or individual fish in
quarantine.

33. Click here to learn more about koi diseases and
their treatments.
Clearly there are quite a few little
“beasties” out there that can make life
miserable for your koi. The good news is
that there are a lot more options for
treatment these days than there was say
100 years ago.
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