Koi Info Main
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
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
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
Costia normally only affects fish
that have already been debilitated
by some other cause, and can often
be seen on Koi as a secondary
A high magnification must be used to
view these parasites (300 x) and
staining is recommended for positive
Recommended treatments include
Potassium Permanganate, Acriflavine
and strong salt baths of 3% (4 and
one half oz. per gallon)
Cotton Wool Disease
(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 leading to
ulcers and a thin appearance.
Often mistaken for a fungal
infection because of its mold-like
lesions, Columnaris is a common
bacterial infection in cultured
fish, particularly live-bearing fish
and catfish. Its name is derived
from columnar shaped bacteria, which
are present in virtually all pond
The bacteria are most likely to
infect fish that have been stressed
by such conditions as poor water
quality, inadequate diet, or
handling and shipping. Columnaris
can enter the fish through the
gills, mouth, or via small wounds on
the skin. The disease is highly
contagious and may be spread through
contaminated nets, specimen
containers, and even food.
Treatment with anti bacterial
medicine is usually effective.
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 internally in
the fish. There are multiple
possible causes. Sometimes it's not
contagious, but sick fish should be
isolated and treated since
determining the actual cause may be
impossible, and also because this
will be easier on the fish.
The fish's body will become swelled
with fluid it is unable to expel.
Eventually the swelling will cause
the scales to raise, giving the fish
what is called the "pine-cone"
Diagnosis, One of these situations
may be the cause:
• Sudden swelling: A bacterial
infection will cause internal
• Slow swelling: Growing tumors, or
even parasites, in the fish may
cause it to swell.
• Slow swelling: Mycobacterium
tuberculosis. Highly contagious!
dropsy is infectious so treat with
an anti bacterial remedy and if
possible isolate affected Koi.
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 further
damage, and fungal infection can
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
litter 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
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
If they infect the gills they cause
severe damage and often death. Most
anti-parasite remedies will not kill
fish lice, a strong chemical is
needed which is not freely on sale.
Ask a professional dealer or vet.
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
Heavy infestations can cause severe
damage, eroding the gill filaments
and allowing secondary infections to
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
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
Skin and Gill
and Skin flukes are two of the
family of monogenetic trematode
genera, all of which are
characterized 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.
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
It attacks both skin and gill
tissues of our Koi, and can often
cause more damage to gills than
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
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.
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