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Parasite
treatments in koi, goldfish and other pond fish |
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Alan Levington (copied with
permission)
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| Parasites in koi ponds can often cause serious
problems for the koi, and keeper alike. By this statement I mean, that the fish
have the parasite problem, and the keeper has the problem of curing it! Knowing
which parasite or parasites are present is essential for the application of the
correct remedy. In order to be able to
control levels of fish parasites in ponds, it is necessary to understand
something of their life cycles. Understanding how they reproduce, and what their
various life stages are, can sometimes allow us an opportunity to seriously
reduce their numbers.
A microscope can assist in making a precise
initial diagnosis of the problem, and as you will appreciate from the following
text, further microscope tests are preferable in order to apply follow up
treatments which are necessary with some parasites, such that the reproductive
cycle of the parasite is broken. You may well appreciate that the subjects in
the title of this article are closely linked.
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|
Environmental Conditions |
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Problems with parasites are usually associated
with either new introductions to the pond or some environmental problem such as
low oxygen levels, nitrite or high nitrate levels. Low oxygen levels can
severely stress fish and can be caused in several ways.
Low oxygen levels are more likely to prevail in
summertime, when temperatures are higher, although some treatments for parasites
can target algae and pond debris as part of the chemical reaction aimed at the
parasites, and in so doing, create oxygen shortages.
It is wise to increase aeration in the pond
before, during and after any medications are used. As fish consume approximately
four times more oxygen after feeding, it is best that food is withheld for the
duration of any treatment.
Simply overfeeding the fish can cause nitrite
levels to rise above normal levels, or it can happen when the stocking level is
in excess of that which the biological filter can cope with. Low oxygen levels
and low KH frequently lead to nitrite levels rising. The whole pond system
relies upon oxygen to function and adequate resources of calcium carbonate are
essential to the bacterial activity of the filter. In systems operating in areas
where the water is soft, and winter and spring pond care is kept to a minimum in
terms of water changes, the borderline level of calcium carbonate can be
reached. If this happens, the increased activity within the pond can use up the
remaining carbonates and biological filtration problems can occur.
Nitrate is the end product of the biological
filter function and can be controlled by regular water changes. Test kits are
available for measuring all the water parameters mentioned.
Frequent parasite problems would tend to
suggest that the environmental factors within the pond are less than ideal. Fish
living in a pond with good water parameters are able to cope with the small
levels of parasites, which are often present in small numbers in perfectly
healthy ponds.
It is difficult to take any one subject, which is part of the overall scene of
keeping koi, without the subjects overlapping with other subjects relating to
the koi pond.
Low oxygen levels and nitrite contributing to a
parasite problem – never!! Or so you may have thought before reading the above
facts.
Carp did not evolve naturally in Europe, due to
this they have not fully adapted to climate here. They evolved where winter
temperatures are 14C and summer temperatures can reach 25C. Due to this their
immune systems have evolved to operate in this temperature range.
At low temperatures very little activity occurs
in a pond, bacteria, parasites and fish are all relatively inactive. However
once temperatures begin to rise all activity increases. This can cause problems
for a koi carp because the increased bacteria and parasite activity are
occurring before the koi’s immune system is able to react to this threat.
Bearing this in mind all koi keepers should be particularly vigilant in the
springtime.
Some keepers take the prophylactic approach:
they rid the pond of any undue organic waste, and rid the koi of as many
parasites as possible in the late autumn when temperatures are still above 15C.
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| Signs of Disease |
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Most parasites will cause fish to react in a
similar fashion. Points to watch for would include the following:
Fish remains alone and ceases to be a sociable
shoal fish.
Fish jumping or scraping against pond side and
floor.
Fish refuses to feed.
Fish breathes heavily, opening and closing of
the mouth and gills.
It is possible to have parasites in a pond and only one, or a few of the fish
seem to be affected. As individuals they can differ in personality as well as
their ability to resist disease and parasites.
If this is seen to happen, it is possible to
treat an individual by way of a salt bath. Seawater contains about 3% salt. The
bodies of freshwater parasites contain about 0.5% salt solution. Osmosis is a
simple physics fact which guaranties that water will always tend to go towards
an area of high salt concentration. In a salt bath of water of 3% solution, the
parasites, being simpler creatures than the fish, can have the fluids withdrawn
from their bodies by this difference in salt concentration. The same laws of
osmosis exist for the fish so care and continuous observation of the fish during
this treatment is essential. Once the fish begins to lie over on its side in a
similar manner to that which occurs when a fish is anesthetized, it should be
removed from this salt bath and placed into another container to recuperate. A
maximum of two minutes is advised for this treatment which can be repeated if
necessary a short time later.
An improvement in the disposition of a fish
after this treatment can suggest that parasites may be the problem.
In the wild, fish can often rid themselves of parasites by changing where they
live in a lake. River fish can have parasites washed downstream where they can
no longer infect them. However, in a closed pond system, the detection of a
parasitic infection is best dealt with by the appropriate treatment. Always
check water parameters first if fish behave in an unusual manner.
Spring variations in temperature can stress
fish. They have evolved to expect quite stable temperatures, which change very
slowly with the seasons. Large bodies of water resist temperature changes much
better than small ponds.
The first parasite to be discussed is "White
spot". This parasite is frequently seen after sudden drops in water temperature.
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| Preparation of a
microscope slide |
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One of the main reasons for failure to detect
parasites on a skin scrape is incorrect preparation of the slide sample. The
following tips should help in taking a sample of mucus from the fish and
preparing the slide.
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| Samples of mucus
from the skin |
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Net the fish and gently use the glass slide to
remove a small amount of mucus from the surface of the skin. The term "skin
scrape" is misleading as you are only taking a small sample of mucus which
covers the skin.
Samples of mucus from the gills. Caution - the
gills of a fish equate to the lungs of a terrestrial animal. Extreme care must
be exercised whenever gill samples are taken.
Taking samples from the gills is a very
delicate operation and many inexperienced koi keepers will avoid this task.
Dead, whole fish are sold in most supermarkets and a practice run on one of
these may help in training for the real job,
If a sample of mucus is required from the
fish’s gill, the fish must first be anaesthetized. Once the fish is motionless
the gill cover can be raised and the glass slide very carefully inserted between
the layers of gill tissue to collect a sample of mucus. Scraping it together
using a cover slip should collect this tiny quantity of mucus, which is on the
glass slide. Add a small amount of water to the sample and cover with the cover
slip. Gently press the cover slip onto the slide until the sample spreads
outwards towards the cover slip edge. On small fish, a wet cotton bud or a small
loop of wire may be used to gently remove a sample of mucus from the gill.
Always begin searching a slide with the microscope at the lowest power setting.
This is usually 30/50X magnification. If the slide has been prepared correctly
as above you will be looking at what is best described as an aerial view of a
coastline with perhaps several islands lying off this "coast".
Any large parasites should be visible at this
magnification. Typically, mature forms of "White spot" and gyrodactylis (skin
fluke) would be visible.
A further search of the slide at a higher
magnification of100X will reduce the amount of mucus sample visible through the
microscope, as it appears to bring the sample closer to view.
Further explanations are given on
identification as the various common parasites are discussed. It should be said
that the major problem for anyone learning to use a microscope is what to ignore
as "normal". Later explanations and photographs taken through the microscope
should help with firm identification of individual parasites
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| White Spot |
(photos done with microscope and digital camera) |
| One of the most common of all fish diseases is
known as "White spot" or "Ich". The latter name is a shortened version of the
name of the parasite "ichthyophthirius multifiliis".
The common name "White spot" was given by aquarium
keepers due to the fact that badly infected tropical fish could be seen with
white spots on their bodies. These white spots are rarely seen on koi unless the
infection is severe and well advanced: suspicion of the disease is by
characteristic changes in the koi’s behavior and diagnosis is confirmed by
microscopic examination of skin/gills scrapes
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| Life Cycle |
| Ich has an interesting life cycle, one stage of which
is illustrated in Fig 1. At this stage of the life cycle it is quite easily seen
on skin/gill scrapes, however at another of its life stages it bears no
resemblance to Fig 1. Being comparatively small and of an entirely different
shape, it is often not recognized. Stage 1. For
simplicity we will take the stage shown in Fig1 as the first stage of the life
cycle of Ich. Once maturity has been reached at stage1. the parasite leaves the
fish and drops to the pond floor where it covers itself with a protective
coating and continues to develop.
Utilizing energy, which it has gained from feeding on
the fish’s tissue, it divides into numerous individual "tomites" or baby "Ichs".
From 500/1000 individual tomites can emerge from this one encapsulated
individual. These are frightening numbers, but as this parasite has evolved to
meet natural stocking levels, it produces these huge quantities to increase the
chance of one individual finding a host and continuing the cycle, much the same
as trees and flowers produce large quantities of seed on the off chance that one
will find a suitable place to grow and perpetuate the tree or flower species.
On leaving the capsule the tomite becomes free swimming
and searches for host. At this time it is extremely small. If a fish is not
found within a short time the tomite will die. If it finds a fish it can use
this as a food source and will grow once again into the relatively large, easily
recognizable form of Ich, and so the cycle continues.
If the number of fish available for the tomites to
colonize is large, there is obviously a much greater chance of them being
successful in their attempts at finding a new host fish. In koi ponds we stock
at much higher densities than would normally be found in natural environments,
hence the risk of re infection is much greater A few parasites would cause
little harm to a fish, but once numbers increase significantly the fish soon
becomes distressed and if treatment is not applied quickly, serious skin and
gill damage will occur which can kill the fish.
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| Treatment |
| The preferred treatment for Ich is Malachite
Green at 0.1 grams per ton (0.1gram/1000litres i.e. 0.1ppm) together with
formalin at 15ml/ ton (15ml/ 1000 litres i.e. 15ppm). Commercial preparations of
these chemicals are available and the instructions should be followed according
to pond size. This treatment will kill
the parasite whilst it is in the free-swimming stage and on the fish, but when
the parasite is in the encapsulated stage on the pond floor, it is protected
from any know treatment that would kill it without affecting the fish.
Typically, if malachite green and formalin were
used, this would kill of all visible stages of this parasites life cycle, and a
microscopic examination following this treatment would give negative results.
The temperature of the pond governs the rate at
which Ich develops. Sometimes instructions for treatment, give application
times, which are based upon aquarium temperatures of 21C. At pond temperatures
the cycle is much slower.
In order to successfully eradicate Ich, it is
essential to be able to detect two of the life stages, one of which is shown in
Fig1. The other is shown in Fig2.
It is difficult to believe that the creature in
Fig2 is even distantly related to that shown in Fig1, but it is. Careful use of
the microscope is essential to determine the right time for the second treatment
of malachite and formalin, which will kill the emerging tomites and early
colonies of the parasites on the skin and gills.
The immense increase in size as the parasite
develops, gives a fair indication of the nutrients, which it takes from the
fish.
.Being so small it is quite difficult to
achieve clear pictures as this tiny form of the parasite is in continual motion.
This motion is best described as "swimming about" whereas other parasites such
as costia move with a definite flickering motion.
Once the tomites are seen on the scrapes, it is
the correct time to apply the second treatment of the same malachite and
formalin mix. As stated earlier, the temperature of the pond influences the rate
at which the parasite develops. An approximate time for the second treatment at
10C would be 14/21days. At 15C - 10/12 days, and at 17C -7/8 days.
It would be a wise precaution to continue to
examine any fish showing signs of unusual behavior incase late developing cysts
release tomites after the above stated times.
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|
| Costia |
| Costia is found on both the skin/fins and in
the gills where it can cause serious damage. Like several other parasitic
infections it can cause the infected fish to rub their gill plates on the pond
floor and sides, together with any other protrusions in the pond. Fish, which
are infested with costia often, produce extra mucus and have a grey "bloom" on
their skins. However this can be caused by other parasites too so it cannot be
taken as a precise diagnosis for costia.
It is a very small parasite but can often be present in such high numbers that
the typical flickering motion can be seen, A magnification of at least 100X is
needed to detect this parasite: 400X is recommended for positive identification
once the very tiny flickering motion is detected. Careful preparation of the
slide is essential. Avoid thick mucus preparations and add a little pond water
to the slide if necessary such that a thin mucus sample is observed with plenty
of "coastlines".
Search along this "coastline" for tiny
flickering movements, which are a typical indication of the presence of costia.
Two types of costia are believed to infest
fish; one prefers the gills as a site of infection whereas the other prefers the
skin. Both are described as "kidney" to "bean" shaped and 10-20microns long,
having flagella from 9-18 microns long. (Twenty millionths of a meter long.)
(Flagella are whip like hairs, which are used to propel it.)
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| Life Cycle |
Both types have simple life cycles in that they divide
themselves into two individuals to multiply their numbers: this is known as
"binary fission". Costia does not have any intermediate stages but can infect
other fish by contact. It can only live for a short while away from a host fish.
However, to complicate things a little, costia can hide from treatments by
residing in the anus of the fish, only to reappear a short while after
treatment. It is not a forgone conclusion that this will happen, but a series of
scrape tests is advisable following treatment.
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| Treatment |
| The best recognized treatment for costia is potassium
permanganate added to the pond. Potassium Permanganate is a harsh treatment for
fish so it is essential that the correct dose be administered.
One and a half grams/ton (1000 litres) i.e. 1.5 ppm, is considered to be a safe
effective treatment, which will do a minimum of damage to the biological filters
of re circulating pond systems. In order to minimize damage to the filter
bacteria (especially that which deals with nitrite) the water should not be
circulated through the filters until some of its energy has been expended. If
possible re-circulate the filters for first two hours of treatment.
After mixing the chemical with a bucketful of pond water
it should be left for approximately half an hour before it is added to the pond.
Once mixed in the bucket it will turn the water to a deep purple color. When
added to the pond it will make this water purple too. If a pond contains
relatively high amounts of organic matter (algae, fish waste etc) the
effectiveness of the treatment may be reduced due to the oxidizing effect of the
chemical being used up on this matter instead of the costia. A reasonable
indication of the effectiveness is the length of time it takes for the pond
water to change from purple to pink and then to a brownish tea color. If the
pond water becomes "tea colored" in less than four hours, it may be necessary to
repeat the treatment 24 hours later or after substantial water changes. Care
must be taken not to excessively change the water temperature when this is being
done.
Careful use of the microscope will confirm the
effectiveness of the treatment.
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|
| Chilodonella |
|
(photos done with microscope and digital camera) |
| This is another parasite, which can do serious
harm to the gills of a fish; it can also cause severe irritation to the skin
This parasite has a typical way of moving which helps identification under the
microscope. It tends to stop moving in any particular direction then turns
around in a full circle as if pivoted from one end. It is roughly heart shaped
and propels itself using cilia that are located at the thinner end of the
parasite.
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| Life Cycle and
Treatment |
It is believed to multiply by binary fission
and is fairly easy to eradicate by the application of malachite and formalin as
described for "White spot".
It is one of the few parasites, which are eradicated by salt at 0.5%, and the
author has never seen a parasitic problem with koi carp, in re-circulated filter
systems where chilodonella alone is involved. On the rare occasions that it has
been seen on slides, it has not been present in large numbers. However, it is
reported to cause problems in young fish, and may cause problems in ponds with
high organic matter.
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|
| Skin Flukes
(Gyrodactylis) |
|
(photos done with microscope and digital camera) |
Skin flukes are a common parasite of koi and
can cause severe skin irritation, which encourages the fish to rub itself
aggressively on any protrusion within the pond. This can lead to damaged skin,
and bacterial and fungal infections may follow.
They are readily recognized on skin scrapes at a magnification of 30X.
At 100X the large hooks with which the fluke anchors itself to the fishes skin
can be clearly seen. Inside the adult fluke, the young gyrodactylis can usually
be seen together with its attachment mechanism, which may be mistaken for
another attachment mechanism in the mid section of the adult fluke.
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| Life Cycle |
The life cycle of Gyrodactylis is particularly
interesting in that each adult parasite carries within it another smaller
Dactylogyrus to which it gives birth. This young parasite has yet another embryo
within it. The rate at which the parasite reproduces increases with temperature
within the normal temperature range.
Being a livebearer, once the adult is killed the cycle is broken.
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| Gill Flukes
(Dactylogyrus) |
| Gill flukes are also a common parasite of koi
carp. They irritate the gill membranes and can cause the fish to aggressively
rub its gill covers against any suitable surface in an effort to relieve the
irritation. Severe gill damage can be caused if remedial action is not taken.
These flukes are rarely seen on skin scrapes as adults. However the small
juvenile stage can sometimes be seen. Having hatched from the egg this
stage becomes free swimming and searches for a new host. If a host fish is not
found within a 24hr period, it dies.
Once it finds a host, it crawls along the skin
in a similar manner to a caterpillar until it reaches the gills where it
attaches to a gill filament using small attachment hooks located at one end of
its body. Utilizing the fish’s tissue as food, the young fluke grows quickly to
reproductive age and re commences the cycle. Comparing the photographs of the
juvenile and adult gill flukes clearly shows the vast growth achieved from the
egg to adult stage. As was indicated in the section on "White spot" it is
difficult to associate the two stages as being those of the same animal.
The larval and juvenile stage is sometimes eradicated by malachite and formalin
but this is not a reliable way of terminating an infection of this parasite.
Gill scrapes can sometimes reveal the presence of these flukes but this is not a
reliable method of detection. Identification of the juvenile stage on the skin
is reasonably easy. They can be seen as small moving objects at a magnification
of 30X. Once suspected, they can then be examined at 100X and are confirmed as
gill flukes at this stage by the four "eye spots" at one end of the body. (See
Photo)
The adult gill flukes are readily seen in
sections of gill removed from a dead fish.( See Photo) Dactylogyrus is clearly
differentiated from Gyrodactylis by comparing their heads. The first one has a
"four point anterior" and the latter has a" two point anterior", i.e. one looks
very much like a paw with four pads, the other like a paw with two pads. It is
not uncommon to find both of these fluke species in the gills.
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| Life Cycle |
The life cycle of the gill fluke differs from that of a
skin fluke in that it lays eggs, which are released into the pond environment
where they develop and hatch at a later date. The rate of development depends on
temperature and it is believed that eggs can survive for long periods in cooler
water temperatures.
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| Treatment |
An effective treatment is now available which will
eradicate both types of flukes at the same time. Used correctly this treatment
is considered safe when applied at the precise dose to a pond.
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| CAUTION –"
SUPAVERM" |
| Although this treatment is considered safe, repeated
dosing with this chemical remedy can kill koi. It is advisable to establish a
good relationship with the supplier of your koi such that advice is sought as to
when or if the koi supplied, have been recently treated with this control
substance. A minimum of 28 days should be allowed between any treatment received
at the koi dealer’s premises and subsequent treatment of the customer’s pond.
Recent studies have shown that the active chemicals in Supaverm remain in the
fish tissue for a considerable length of time.
Water hardness and temperature play a part in the toxicity of this treatment and
although it has been used for several years to control flukes in koi, there is
very little documentary advice on its use.
"Supaverm" is added to the pond at the rate of 2.2ml/ton
(2.2ml/1000litres i.e. 2.2ppm).
This is left in the pond for three days before any water
changes take place. At summer temperatures it is believed that any of the
Dactylogyrus eggs, which hatch during the treatment period, are destroyed. As
the chemical remains in the fish tissue for some time, it is likely that any
gill flukes that hatch and feed on the fish tissue, will succumb to its effects.
CAUTION Goldfish are reported to be killed by this
treatment. Orfe and Sturgeon have been seen to survive with no apparent effect.
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|
| Trichodina |
|
Trichodina
is yet another parasite which can cause serious skin and gill damage. It is
usually associated with a sudden stress condition. This parasite lives within
the pond water where it feeds principally upon bacteria. It is an opportunist
parasite, which will infect fish when their immune systems are not functioning
at optimum level. It is readily detected on skin
scrapes at a magnification of 30X. (see photo) When alive, this parasite dashes
about resembling the proverbial "flying saucer", when dead it resembles a circle
with hairs or teeth around its circumference. The cilia, which are positioned
around the circumference, are used to propel the parasite.
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| Life Cycle |
Like Costia, Trichodina multiplies by binary fission.
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| Treatment |
| The same treatment is used as for Costia. That is
Potassium Permanganate added to the pond water at 1.5ppm.
This will eradicate Trichodina from the fish and the water column.
Springtime considerations
Although parasites can appear at any time of the year,
the early spring is often when they cause the most concern. Koi, having endured
a winter period without full immune system protection, are vulnerable to
parasitic and other infections at this time.
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|
| Conclusion |
|
A script, which refers to parasites, would be incomplete
without an emphatic statement that the appearance of parasites in large numbers
in an established pond system, generally indicates that the system is somehow
"out of balance".
It should also be stated that disease and parasites are
always present, even in the healthiest pond – they are part of the natural order
of things.
A severe outbreak of parasites requires treatment. However, in any disease
outbreak it is essential to identify the prime cause, which created this state
of "un ease". It is important to understand that all treatments, which kill
parasites, will at the very least, lightly poison the koi too.
I shudder to think how many koi deaths have occurred because of repeated and
unsuccessful treatments for parasites without a thorough and determined search
for the prime cause of them, which is usually an environmental factor.
In some ways the parasites of koi are fascinating creatures and observing them
through the microscope opens up a whole new world to us. Interesting they may
be, but welcome they are not, - in my ponds anyway!
Alan Levington
Notes on Author
Alan began keeping koi twenty years ago when little information was available to
koi keepers on how o control parasitic infections.
He has spent much time studying the various parasites of freshwater fishes both
in natural lakes and koi ponds. Invariably the environment and overstocking of
various fish species has always been the major factor in any disease outbreaks.
He is aware of the limitations of fish keeping in
filtered and re circulated systems, but remains enthusiastic that even though
optimum conditions may never be reached which compare with a natural balanced
pond, better than minimum survival conditions can be achieved.
Alan now runs a Koi outlet in County Durham where both
high quality koi and sensible advice are available.
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