Group Title: Circular
Title: Ichthyophthirius multifiliis (White spot) infections in fish
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 Material Information
Title: Ichthyophthirius multifiliis (White spot) infections in fish
Series Title: Circular
Physical Description: 3 p. : ill. ; 28 cm.
Language: English
Creator: Francis-Floyd, Ruth
Reed, Peggy
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1991
Subject: Ichthyophthirius multifiliis   ( lcsh )
Fishes -- Diseases   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: Ruth Francis-Floyd and Peggy Reed.
General Note: Title from caption.
General Note: "Printed 3/91"--Colophon.
 Record Information
Bibliographic ID: UF00014504
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA6944
ltuf - AJG5665
oclc - 26846452
alephbibnum - 001752708
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Circular 920


Ichthyophthirius multifiliis (White Spot)
Infections in Fish

Ruth Francis-Floyd and Peggy Reed

Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, dean

Ichthyophthirius multifiliis, is a ciliated proto-
zoan which causes "Ich" or "white spot disease".
This disease is a major problem to aquarists and
commercial fish producers world wide.
Ichthyophthirius is an important disease of tropical
fish, goldfish, and food fish. The disease is highly
contagious and spreads rapidly from one fish to
another. It can be particularly severe when fish are
crowded. While many protozoans reproduce by
simple division, a single "Ich" organism can multi-
ply into hundreds of new parasites. This organism
is an obligate parasite which means that it cannot
survive unless live fish are present. It is capable of
causing massive mortality within a short time. An
outbreak of "Ich" is an emergency situation which
requires immediate treatment: if left untreated,
this disease may result in 100% mortality.

The parasite
"Ich" is the largest known parasitic protozoan
found on fishes. Adult organisms are oval to round
and measure 0.5 to 1.0 mm in size. The adult is
uniformly ciliated and contains a horseshoe-shaped
nucleus which can be seen in older individuals.
The breeding stage of the parasite encysts
between the layers of the host skin. When mature,
it leaves the fish and produces large numbers of
free swimming young. These must find a host
within 48 hours (at water temperatures of 75-79F)
or they will die. The life cycle of "Ich" is shown in
Figure 1.

Disease signs
The classic sign of an "Ich" infection is the
presence of small white spots on the skin or gills.
These lesions look like small blisters on the skin or

Figure 1. Life cycle of Ichthyophthirius multifiliis. Chemical
treatment is only effective against the free-swimming juvenile
parasites (tomites) shown on the left. To control the disease
multiple treatments are necessary to continually remove
tomites and prevent reinfection. Siphoning debris from the
bottom of a tank will remove cysts before tomites emerge, thus
decreasing the number of tomites in the environment.

fins of the fish. Prior to the appearance of white
spots, fish may show signs of irritation, flashing,
weakness, loss of appetite, and decreased activity.
If the parasite is only present on the gills, white
spots will not be seen at all, but fish will die in
large numbers. In these fish, gills will be pale and
very swollen. White spots should not be used as the
only means of diagnosis because other diseases may
have a similar appearance. Gill and skin scrapings
should be taken when the first signs of illness are
observed. If the "Ich" organism is seen, fish should
be medicated immediately because fish which are
severely infected may not survive treatment.

IFAS extension veterinarian, Department of Large Animal Clinical Sciences and Department of Fisheries and Aquaculture; Biological
Scientist in the Department of Large Animal Clinical Sciences, Gainesville, Florida 32611.

Diagnosis of "Ich"
Diagnosis of"Ich" is easily confirmed by micro-
scopic examination of skin and gills. Remove
several white spots from an infected fish, then
mount them on a microscope slide with a few drops
of water and a cover glass. The mature parasite is
large, dark in color (due to the thick cilia covering
the entire cell), and has a horseshoe-shaped nucleus
which is sometimes visible under 100 x magnifica-
tion (Figure 2). The adult parasite moves slowly in
a tumbling manner and, with practice, is easily
recognized. The immature forms (tomites) are
smaller, translucent, and move quickly. The tomites
(Figure 3) closely resemble another protozoan
parasite called Tetrahymina (Figure 4).
Tetrahymina usually does not require treatment, so
it is important to recognize the difference between
the two parasites. If only tomites are seen, prepare
a second slide and examine it closely for the adult
parasite to confirm the diagnosis. Observation of a
single organism is sufficient to make treatment

AP 0

o I 0

Figure 2. Adult stage of Ichthyophthirius multifiliis. The
parasite is large (1000m), covered with cilia, moves in a
characteristic ameboid (tumbling) manner, and has a
horseshoe-shaped nucleus.

Figure 3. Immature "Ich". These juveniles emerge from a cyst
and swim-up seeking a new host. If a fish is not found within
48 hours (at water temperatures of 75-79C), they will die. This
is the only stage of the life cycle where the chemical treatment
will remove the juveniles.

Figure 4. Tetrahymina is a ciliated protozoan commoit
in detritus and on dying fish taken from the bottom o
vat. It is important to distinguish this organism from j
of multifiliis. Although tetrahymina can cause disea
often an incidental finding if only found externally on
removed from the bottom of a tank.

Prevention of "Ich"
Prevention of "Ich" is preferable to treatii
after a disease outbreak is in progress. All i:
coming fish should be quarantined for at les
days when temperatures are 75 to 83F. At
temperatures a 3-day quarantine will be inE
for "Ich" because of its lengthened life cycle.
reason, and to prevent introduction of other
which have incubation periods greater than
a longer quarantine is strongly recommend(
weeks is generally considered a minimum p
adequate quarantine of new fish.

Treatment of "Ich"
Control of "Ich" outbreaks can be difficult
of the parasites' unusual life cycle and the e
water temperature on its life cycle. Review 1
cycle ofl. multifiliis presented in Figure 1. 4
life stages shown, only the free-swimming tb
are susceptible to chemical treatment. This
that application of a single treatment will k
tomites which have emerged from cysts and
not yet burrowed into the skin of host fish. 9
single treatment will not effect organisms w
emerge after the chemical has broken down
flushed from the system. Repeated treatmer
however, will continually kill the juvenile to
preventing continuation of the infection. Th
epizootic will be controlled as more adult pa
drop off the sick fish, encyst, and produce yc
which cannot survive because of the repeated
application of chemicals. This process will b4
accelerated if organic debris can be removed
the tank or vat following treatment. This wil
remove many of cysts from the environment,

creasing the number of emergent tomites.
Water temperature has a tremendous influence
on how fast the life cycle for "Ich" (Figure 1) is
completed. At warm temperatures (75-79F), the
life cycle is completed in about 48 hours, which
means that chemical treatments should be applied
every other day. At cooler temperatures the life
cycle is prolonged and treatments should be spaced
further apart. For example, at a water temperature
of 600F, treatments should be spaced 4 or 5 days
apart. In warm water, a minimum of three treat-
ments applied 2 to 3 days apart is required. In
cooler water, a minimum of five treatments should
be applied 3 to 5 days apart. Treatments should
never be discontinued until all mortality from "Ich"
has stopped. Fish should be closely watched during
recovery; the weakened fish may be susceptible to a
secondary bacterial infection. The choice of chemi-
cal used to treat "Ich" will be based upon water
quality conditions, species of fish to be treated, and
the type of system fish are housed in. In general,
copper sulfate, formalin, and potassium permanga-
nate are all effective against "Ich" when applied at
the correct concentration in a repetitive manner as
described above.

Special considerations for
treatment of food fish
Most channel catfish, raised in the southeast,
are reared in ponds. For these fish, the treatment
of choice for "Ich" is copper sulfate. The chemical is
effective and relatively inexpensive, an important
consideration when large volumes of water are
treated. The disadvantage of copper sulfate is that
it is extremely toxic, particularly in water of low
alkalinity. NEVER use copper sulfate without
testing the total alkalinity of the water, carefully
measuring the dimensions of the pond to be
treated, and weighing the amount of chemical to be
The concentration of copper sulfate to apply is
often calculated by determining the total alkalinity
of the water and dividing that number by 100. For
example, if the total alkalinity of the pond is 100
mg/L, then 100/100 = 1 mg/L copper sulfate. Do not
use copper sulfate if the total alkalinity is less than
50 mg/L. If you have never used copper sulfate,
contact an IFAS extension aquaculture specialist
for assistance. Use of copper sulfate may lead to
severe oxygen depletions, therefore, emergency
aeration should always be available. Use of copper
sulfate during hot weather, or when algae blooms

are dense, is strongly discouraged. Remember, if
you do not know the alkalinity of your water and
can not measure it then DO NOT USE COPPER
If you are unable to use copper in your pond
because of low alkalinity, lack of aeration, or you
are not comfortable using it, potassium permanga-
nate can be used instead. The primary disadvan-
tage of potassium permanganate is its high cost.
However, it is equally effective and safer to use
than copper sulfate. Potassium permanganate can
be applied at a concentration of 2 mg/L which will
result in a purple-pink color of the water. If the
water turns yellow or brown in less than 8 to 10
hours, then the treatment should be repeated.
Usually, a maximum of three applications (2 mg/L
each) is recommended during any one treatment
(maximum concentration of 6 mg/L).
If fish are maintained indoors in a tank system,
formalin can be used to treat "Ich". Formalin is not
the ideal treatment for ponds, but works nicely in
tanks with vigorous aeration. Formalin should not
be run through a biofilter, however, as it will kill
the bacteria in the filter and ammonia levels may
increase to lethal levels. A short-term bath of 250
mg/L for 30 to 60 minutes can be followed by a
water change. Cleaning the tank will also decrease
the number of parasites. When applying a concen-
trated treatment such as formalin, NEVER leave
the fish in the treated water longer than recom-
mended, and NEVER leave them unattended. Sick
fish may be unable to tolerate a full treatment. If
they appear stressed or try to jump out of the tank,
flush the chemical from the system immediately. A
long term bath of formalin can be used in a tank
system at a concentration of 15 mg/L and does not
need to be flushed out.
Salt can also be used to control "Ich" infections
in small volumes of water. This is not practical in
ponds because even a light salt solution of 0.01%
(100 mg/L), would require large quantities of salt
(272 lbs/acre-foot). In small volumes (i.e. tanks or
vats), however, salt can be useful. Fish can be
dipped in a 3% (30,000 mg/L) solution for thirty
seconds to several minutes, or they can be treated
in a prolonged bath at a lower concentration (0.05%
= 500 mg/L). Salt at low concentrations (0.01 to
0.05% solution) is an excellent means of controlling
"Ich" in recirculating systems without harming the
biofilter. An ultraviolet filter is recommended as an
aid in preventing the spread of the parasite in a
recirculating system.


Special considerations for
treatment of ornamental fish
Fish which are not intended for human con-
sumption can also be treated with the chemicals
described above for food fish. Copper sulfate or
potassium permanganate work well in pools,
whereas, formalin or salt may be easier to use in
smaller volumes of water.
Malachite green is another chemical which can
be used to treat ornamental fish that are housed
indoors. This chemical should NEVER be used to
treat food fish. Not only is this illegal and unethi-
cal, but it is totally unnecessary. The chemicals
listed above (copper sulfate, potassium permanga-
nate, formalin, and salt) are all excellent treat-
ments for "Ich". Malachite green is mentioned for
the sake of completion, but is not recommended by
the authors. The chemical is hazardous to handle -
it is known to cause cancer, mutations, and is
harmful to fetuses. Gloves and a protective mask
should always be worn when handling the concen-
trated powder. Pregnant personnel should NEVER
handle this chemical. Despite its toxicity, it is
commonly used to control parasitic protozoans on
ornamental fish and is quite effective when used at
concentrations of 0.05 to 0.10 mg/L as an indefinite
bath. This chemical is extremely harsh on fish,
particularly on gill tissue, so be careful not to
overdose the fish. Malachite green can also be
combined with formalin (0.2 mg/L malachite green
mixed with 25 mg/L formalin) to treat external
protozoan diseases. The two chemicals work well
together and are quite effective. Malachite green
can be very toxic to scaleless fish and should be
avoided on these species.

Special considerations for
treatment of pet fish
Pet fish can be treated with any of the chemicals
discussed above to correct "Ich" infections. A
number of commercial preparations are available
from pet stores which contain one or several of
these agents. Temperature manipulation is also an
effective way to control "Ich" in home aquariums.
This technique is often not practical for commercial
fish farms, but is advantageous for the hobbyist
because expensive products do not have to be
purchased and it is safer for some of the delicate
species which are popular in community tanks.
Water temperature can be gradually raised to 90F,
maintained there for 24 hours, and then gradually

dropped to 70F for 48 hours. The infective juve-
niles (tomites) will be killed while the water
temperature is at 900. When the temperature is
dropped the adult organisms will fall off the fish
and begin to reproduce. As the young begin to
emerge 48 hours later, the temperature is again
raised to 900 F, causing them to die. Repeating this
process continuously (24 hours at 900 F followed by
48 hours at 700 F) for two weeks should control the
disease. Cleaning the tank every second day will
help remove cysts before they rupture and there-
fore help to prevent completion of the life cycle. If
you decide to use temperature to control "Ich" in
your home aquarium be sure that the type of fish
in your tank can tolerate the temperature ex-
tremes involved.

"Ich" is a protozoan parasite with the scientific
name of Ichthyophthirius multifiliis. It is easily
introduced into a fish pond, tank, or home
aquarium by new fish or equipment which has
been moved from one fish-holding unit to another.
Quarantine is an effective way of preventing this
disease. Once the organism gets into a large fish
culture facility, it is difficult to control due to its
fast reproductive cycle and its unique life stages. If
not controlled, 100% mortality of fish can be
expected. With careful treatment, the disease can
be controlled, but the cost will be high, both in
terms of lost fish, labor, and the cost of chemicals.
In contrast to most parasitic diseases, where the
decision to treat (or not to treat) is based on the
degree of infestation and other factors, fish infected
with "Ich" (even if only one parasite is seen) should
always be treated immediately. This organism can
only survive if live fish are present for completion
of its life cycle. It can cause massive mortality of
fish within a short time. In severe cases, control
may be impossible. A single treatment is not
sufficient for this disease, as the encysted stage is
resistant to chemicals. Repeating the selected
treatment will disrupt the life cycle and control the
outbreak. Daily cleaning of the tank is also benefi-
cial, as the encysted forms are physically removed
from the environment. Ichthyophthirius multifiliis
is a common parasite which can cause catastrophic
loss in aquaculture facilities. Careful attention to
management practices, such as quarantine and
multiple treatments when outbreaks occur, will
minimize economic loss from this disease.

Director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and June
30, 1914 Acts of Congress; and is authorized to provide research, educational information and other services only to individuals and institutions
that function without regard to race, color, sex, age, handicap or national origin. Single copies ofextension publications (excluding 4-H and youth
publications) are available free to Florida residents from county extension offices. Information on bulk rates or copies for out-of-state purchasers
is available from C.M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before I
publicizing this publication, editors should contact this address to determine availability. Printed 3/91.

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