Marine Ich, an infestation of Cryptocaryon
irritans, is one of the two most common afflictions of
saltwater fish; the other being Marine Velvet caused by Amyloodinium
sp. (Michael, 2002 and Joshi, 2003). In this two-part series,
I will explain some of the biology of this ciliated parasite
and discuss the multitude of treatments, remedies, cures,
and elixirs that have been put forth to save your fish and
sometimes empty your wallet. My hope is to help you wade through
the copious and often erroneous anecdote to find an effective
treatment that best suits your particular needs and that of
Before you can decide on a treatment,
you need to be fairly certain what is the infectious agent
of the fish. Some of the signs of infection with Cryptocaryon
irritans are rubbing or scratching against decorations
or substrate (this behavior is also known as glancing or flashing),
breathing problems, an increased mucous layer, loss of appetite,
abnormal swimming behavior, frayed fins, cloudy eyes, and,
of course, the telltale white spots. These characteristic
spots are usually described as appearing like small grains
of salt stuck to the body of the fish. Even in the presence
of all of these external signs, the best diagnostic tool is
microscopic examination of fresh fin or gill clippings or
skin scrapings. But, realistically, an extremely small number
of us are ever going to perform this kind of differential
diagnosis, myself included.
This disease is usually associated with
several environmental triggers. Changes in water temperature,
exposure to high levels of ammonia, nitrite, or nitrate, low
pH levels, low dissolved oxygen, and overcrowding are all
factors contributing to the onset of the disease. You could
lump all of these in a general category of stress, but I find
it more appropriate to think of all of these as wholly unnatural
conditions. In fact, Cryptocaryon irritans is rare
in the wild, and even more unlikely to be lethal (Bunkley-Williams
& Williams, 1994). Ich is truly a disease that exploits
the conditions of captivity to reproduce and easily find suitable
Cryptocaryon irritans has demonstrated
a very low level of host specificity, meaning it will infect
just about any teleost fish in a tropical marine environment.
Cartilaginous fishes (sharks and rays) appear resistant, but
everything else is susceptible to infection (Colorni &
Burgess, 1997). It has even been proven to infect various
species of freshwater fish that were acclimated to saltwater,
as well as temperate marine fish that were kept at the upper
limit of their thermal range (Yoshinaga & Dickerson, 1994;
Burgess & Matthews, 1995).
Even though they are all possible hosts,
experience has shown that there are definitely certain fish
groups with higher and lower degrees of susceptibility. At
one end of the spectrum are the eels that have shown a general
resistance to Cryptocaryon irritans. On the opposite
side are the surgeonfishes, with the Blue Regal/Hippo Tang
(Paracanthurus hepatus) the "crowned king of Ich."
I have dealt with literally hundreds of these fish, and I
could probably count on one hand the number of Blue Regal
Tangs that appeared to be completely free of infection. I
would also place the cowfish, boxfish, and pufferfish fairly
high on the susceptibility list. Generally, everything else
falls somewhere in the middle.
The lifecycle of the parasite is interesting
and important to understand when evaluating a treatment. The
stage where the parasite is attached to a fish is called a
trophont. The trophont will spend three to seven days (depending
on temperature) feeding on the fish. After that, the trophont
leaves the fish and becomes what is called a protomont. This
protomont travels to the substrate and begins to crawl around
for usually two to eight hours, but it could go for as long
as eighteen hours after it leaves it's fish host. Once the
protomont attaches to a surface, it begins to encyst and is
now called a tomont. Division inside the cyst into hundreds
of daughter parasites, called tomites, begins shortly thereafter.
This noninfectious stage can last anywhere from three to twenty-eight
days. During this extended period, the parasite cyst is lying
in wait for a host. After this period, the tomites hatch and
begin swimming around, looking for a fish host. At this point,
they are called theronts, and they must find a host within
twenty-four hours or die. They prefer to seek out the skin
and gill tissue, then transform into trophonts, and begin
the process all over again (Colorni & Burgess, 1997).
Many hobbyists are fooled into believing
they have cured their fish of the parasites, only to find
Ich present again on fish a few weeks later; a reason why
following through with a full treatment protocol is so important.
Don't make this mistake and be lulled into a false sense of
security. The parasites may be in a stage where they are merely
regrouping and multiplying for their "next offensive."
In the wild, this sort of massive reproductive phase ensures
that a few will find a suitable host to continue on the cycle.
In the close confines of our aquariums, though, it means comparatively
massive infection rates.
There is another interesting observation
I found in my investigations concerning the biology of Cryptocaryon
irritans. Mature trophonts leave the host and tomites
exit the theront/cyst in the dark (Yoshinaga & Dickerson,
1994). Imagine if you will, a fish that randomly acquires
a single Ich parasite. After a couple of days when the trophont
is well fed, it prepares to drop off its host but waits for
the environmental trigger of darkness. Meanwhile, the fish
prepares to "bed down" in its favorite hiding spot
in the aquarium; the same fish occupy the same spot practically
every night. Now, the trophont leaves the fish, encysts, and
begins to multiply. Several days to weeks go by and that same
fish returns to its same spot at night, only this time there
are hundreds of infectious theronts seeking out a host/victim
in the same area. I am sure some of you are thinking that
this is absolutely diabolical. Others can appreciate the simple
beauty of this plan. To me, it is just another reminder of
how remarkable evolution and adaptation is.
Given all of this "planning,"
it seemed strange to me to read that not all the theronts
will be able to find a host. Actually, given ideal laboratory
conditions, only between five and twenty percent succeed,
but that still adds up to an awful lot of parasites. Given
this kind of infection rate and the rate of reproduction,
the total number of parasites can increase approximately ten
times every week (Colorni & Burgess, 1997).
Concerning taxonomy, Cryptocaryon
is currently still a monotypic genus (meaning there is only
one species in this genus). Although, there is research to
suggest that there may actually be several distinct species.
There are at least various isolates from different geographic
regions; even if their differences are not substantial enough
to warrant designating separate species (Colorni & Burgess,
1997). I, and several of my friends in the business, can testify
that there are marked increases in Cryptocaryon irritans
outbreaks and mortalities when mixing fish from the Caribbean
with those of the Indo-Pacific. It is possible that this higher
incidence in problems could be the result of fish that have
evolved a limited immunity against their native variety coming
into contact with an unfamiliar strain of parasite.
The best course of treatment is prevention.
All new fish should be quarantined for at least one full month.
This helps ensure that the fish are healthy, but it also gives
them time to get over any shipping trauma, to get used to
a new diet, and to put on weight after withstanding often
insubstantial feedings at retailers, wholesalers, and collecting
stations. Best of all, this will occur in a competition-free
I have found the best quarantine/hospital
tanks to be bare bottomed (no crushed coral or sand) and decorated
with inert, nonporous, and "easy-to-clean-and-sanitize"
items. Short sections of various diameter PVC pipe work very
well for shelter. Live rock does not meet these criteria and
therefore I do not recommended its use. It is best to not
use any calcareous materials as they will absorb and interfere
with some medications.
There is also another possible benefit
to using all of these smooth, artificial materials in your
quarantine tank. In studying outbreaks of Cryptocaryon
irritans in Brown Spotted Grouper (Epinephelus tauvina)
at an aquaculture station, Rasheed (1989) found that fish
kept in concrete vessels routinely fell victim to Ich while
those kept at the same facility with identical care, but in
fiberglass containers suffered absolutely no infestations.
She theorized that the cyst stage of the parasite found the
smooth sides of the fiberglass tanks inhospitable. While not
proven, it is very interesting and definitely something to
keep in mind. At the very least, this type of setup is extremely
easy to clean and disinfect if necessary.
I prefer to filter the tank with sponge
filters. I usually have one running but tucked away in the
sump of my display tank. This way, I can keep the quarantine
tank empty and packed away in the garage when it is not needed.
Some people may be concerned about the sponge filter acting
as a so-called "nitrate factory", but the amount
of nitrate produced from a comparatively small sponge filter
should be negligible. When I do need to use the quarantine
tank, I merely drain some water out of the display tank into
the quarantine tank, add the sponge filter and a heater (I
generally target 80°- 82°F to speed up the life cycle
of any parasites), and it is ready. You may also want to include
a powerhead into the quarantine setup for fish that require
brisk water movement. The entire setup process should take
less than an hour and save the electricity and space of maintaining
the quarantine tank continuously. Also, keeping the quarantine
tank empty spares the temptation of turning it into a full-blown
reef or fish tank!
If you do not have a sump on your display
tank, a hang-on type filter, such as those with "bio-wheels,"
work well. Keep the bio-wheel running on the display tank
and move it to the quarantine tank when needed. The only precaution
is to remove the activated carbon filter cartridge when using
It is my strong preference and my general
recommendation to never add any medications to a display tank.
In my experience, it is always better to remove all the affected
fish to a separate quarantine/hospital tank for treatment.
This ensures that none of the display tank's other inhabitants
such as corals, bacteria, worms, amphipods, copepods, or mysid
shrimp are affected. Also, if you keep the fish in quarantine
for one month without infection, you can be sure that any
Ich parasites and their eggs have hatched and died without
a host. Note that Cryptocaryon irritans requires a
fish host. They cannot complete their life cycle with the
rock, sand, or any invertebrates.
Some people draw a distinction between
quarantine tanks and hospital tanks, with hospital tanks being
designed like I have described above, and quarantine tanks
much more like displays lacking other fish. I don't draw this
distinction and choose to quarantine all my fish using the
means described above. The theory is that fish kept in a more
natural setting will be under less stress, and therefore more
likely to resist disease. In the event a fish does come down
with a disease, it is transferred to a bare-bottom tank for
treatment. While this may have some merit, I cannot be bothered
running two tanks just for temporarily holding fish.
Treatment Option 1 - Copper:
Copper is a highly effective medication
against Cryptocaryon irritans when dosed and maintained
in the proper concentration. The references I found varied
in their recommended dosage:
Andrews et al, 1988: 0.15-0.30 mg/l
Bassleer, 1996: 0.25-0.30 mg/l
Gratzek et al, 1992: 0.115-0.18 mg/l
Noga, 2000: 0.15-0.20 mg/l
Untergasser, 1989: 0.15-0.20 mg/l*
to be used with Methylene Blue)
I am going to abbreviate my advice and
simply suggest to: "Always follow the directions of the
manufacturer of whichever brand of copper medication you employ,
and always use a test kit to verify the dosages." Copper
has a narrow range of effectiveness and levels must be monitored
at least daily.
Copper has several disadvantages in treating
Ich. First, at too low a dosage, it is ineffective. Secondly,
at too high a dosage, it could kill all your fish. Daily,
or better yet twice daily, testing is required to maintain
an appropriate and consistent level of copper. Even when within
the appropriate ranges, some fish cannot tolerate copper.
Some of the fish more sensitive to copper are lionfish, pufferfish,
mandarins, blennies, and any other scaleless fish. Copper
is also a known immunosuppressive, making fish more susceptible
to secondary infections. Invertebrates are extremely sensitive
to copper and cannot be housed in a tank undergoing this treatment.
Lastly, copper cannot be used in the presence of any calcareous
media. Live rock, sand, crushed coral, and dead coral skeletons
will all adsorb copper, rendering it useless a treatment.
Copper specifically targets the infectious,
free-swimming theront stage of this disease, as being buried
deep in the skin of the host protects the trophonts; the cyst
walls of the tomonts are similarly impervious (Colorni &
Burgess, 1997). Knowing this and the life cycle of Cryptocaryon
irritans, monitoring and dosing as needed in the evening
right before the lights go out is going to be the most effective
method. This should ensure optimal treatment concentrations
at the most beneficial time.
Copper is probably the most popular method
of treating Cryptocaryon irritans, but is not my first
choice. It is far too labor intensive for me to recommend
to the general public, has a large risk of overdose, lowers
the fish's resistance to other diseases, and can cause serious
damage to the kidney, liver, and beneficial intestinal flora
of the fish being treated. Damage to intestinal flora is what
many hobbyists point to as a possible contributing cause for
Head and Lateral Line Erosion (HLLE), although there is currently
no definitive cause of HLLE.
Treatment Option 2 - Formalin:
Formalin can be administered one of two
ways; either in short dips with saltwater or used continually
in a hospital tank. The dosage for the continuous use is 1
ml of the 37% stock solution for every 25 gallons of quarantine
tank water (Bassleer, 1996). I prefer the formalin dip to
continuous use because formalin is a fairly toxic compound.
Also, with no commercially available test kits to monitor
the concentration, it would be difficult to dose an entire
tank and account for evaporation, absorption, etc.
To prepare the dip, I take 5 gallons of
tank water and add to it 3.75 ml of 37% formalin. I also aerate
the water vigorously to ensure there is maximum dissolved
oxygen. The dip should last 30 to 60 minutes. As when using
any medication, it is best to monitor the fish's reaction
and be prepared to act if it appears in distress. When the
dip is complete, net the fish, place it back into the hospital
tank, and discard the dip water. This protocol should be repeated
every other day for two weeks.
I would like to remind readers of a few
precautions regarding the use of formalin. First, it is a
carcinogen. Formalin is an aqueous solution of carcinogenic
formaldehyde gas, so gloves should be worn and the area should
be well ventilated when using it. Secondly, formalin should
not be used if fish have open sores, wounds, or lesions. It
is likely to cause tissue damage to these open wounds. And
lastly, formalin can rob the water of dissolved oxygen. That
is why proper aeration is so crucial. For that reason, do
not use formalin if the water temperature is 82*F or higher
(Noga, 2000 and Michael, 2002).
Treatment Option 3 - Copper & Formalin:
It is possible and sometimes preferable,
like in the case of heavy infestations of Cryptocaryon
irritans and Amyloodinium sp., to use copper in
conjunction with Formalin in a quarantine/hospital tank. The
same warnings about sensitive fish still apply. If a fish
is sensitive to either copper or Formalin, they are not safely
exposed to the combined protocol. At this point, it is "cure
or kill." You will either cure your fish or kill it from
poisoning. It is the most aggressive and dangerous treatment
described in this article.
Treatment Option 4 - Hyposalinity:
Low salinity has been demonstrated to be
an effective treatment against Cryptocaryon irritans
(Noga, 2000). A salt level of 16 ppt or approximately 1.009-1.010
specific gravity at 78-80*F for 14 days was reported to kill
the parasite. I have never experienced problems when placing
fish into a hyposalinity treatment, but have routinely witnessed
fish showing obvious signs of distress when brought back to
normal salinity levels too quickly. For that reason, I try
to limit the specific gravity increase 0.001-0.002 points
One of the alleged benefits of this treatment
is the resulting conservation of energy for the affected fish.
Reef fish have to constantly drink saltwater and excrete the
salt to maintain the proper osmotic balance. Lowering the
salinity of the surrounding environment eases this energy
demand on the sick fish, thereby allowing them to expend more
energy towards fighting the infection (Kollman, 1998 and Bartelme,
2001). On the contrary, keeping fish in low salinity means
that they don't "flush" their kidneys sufficiently.
After long-term exposure, this can cause kidney failure and
kill the fish (Shimek, pers. comm..)
The drawbacks to this treatment are the
same as for many of the treatment options discussed above.
Invertebrates and certain fish will not be able to tolerate
it, so you should not apply a hyposalinity treatment in a
display tank. Sharks and rays are two fish groups that do
not tolerate this procedure. I would also not recommend this
approach in the presence of live rock or live sand. The hyposalinity
treatment will likely kill the worms, crustaceans, mollusks,
and other life in and on the substrate, causing a severe drop
in overall water quality.
I have another word of caution when using
this treatment. I would strongly suggest the use of a refractometer
or perhaps a salinity monitor. Swing arm style box hydrometers
are notoriously inaccurate. The glass, floating style hydrometers
are better, but easily broken. An accurate measure of the
salinity could mean the difference between being inside the
effective treatment range or being too high and ineffective
or too low and jeopardizing your fish.
Even given its few drawbacks, hyposalinity
is a great method of curing infected fish of ich in a proper
hospital tank. Of the treatment options discussed this far,
in my opinion, it is by far the safest. While none of these
options is appropriate for use in a display tank, and all
have their drawbacks, weighing the pros and cons of each leads
me to recommend hyposalinity above the others.
Treatment Option 5 - Daily Water Changes:
John Walsh related this method in a presentation
given to the Pittsburgh Marine Aquarium Society, Inc. It is
safe and effective for all marine fish (Colorni, 1985) and
is my preferred first course of action.
Fish are put into a quarantine/hospital tank and then
everyday for two weeks the tank is completely cleaned and
a 50% water change is performed. While the size of this water
change may concern some aquarists who are not accustomed to
water changes of this magnitude, as long as you are careful
about matching the temperature and salinity, you should not
experience any problems. This method helps to remove the tomites,
tomonts, and theronts from the tank and lessens the chance
of reinfection. The fish should remain in quarantine for an
additional month to ensure the treatment has worked and to
allow them time to gain strength.
This method is best used as a preventative
when a fish is first acquired. It is also useful for mild
infestations or when other more aggressive treatments cannot
be used due to species sensitivity. The best thing about this
kind of treatment is it is safe for all fishes and invertebrates.
One of the other benefits is the daily water changes should
help you maintain optimum water quality and therefore should
stimulate the fish's immune system to combat any secondary
bacterial infections that might be attacking the vulnerable
areas where the Cryptocaryon irritans parasites have
burrowed into the skin. This is in contrast to copper or Formalin,
which are both immunosuppressive, and may actually promote
Variations of this method (and the likely
source for the original idea for the treatment) have been
suggested and used successfully by Colorni (Colorni, 1987
and Colorni & Burgess, 1997). They involve moving the
infected fish between two tanks with the tanks being cleaned
and dried in between uses or removing a sand substrate and
replacing with new sand every three days. I don't like the
idea of handling a sick fish that much using the tank transfer
method. While fishnets are designed to be soft and supple,
it can still be dragged across the fish's eye. I have found
the more you have to manipulate a fish, the more likely it
is to contract a secondary bacterial infection like pop-eye
or cloudy eyes. The substrate removal method is interesting.
The sand is supposed to be an ideal media for attracting the
encysting parasites. Removing the sand every three days removes
the tomonts with it. Utilizing aragonite sand for this purpose
is expensive (unless you happen to live somewhere that Southdown
sand is readily available) and very messy. Silica sand is
widely available, cheap, and will create slightly less cloudy
water, but it is still not as clean and easy as the water
change method. I have found the water change protocol to be
just as effective and considerably more practical than either
of Colorni's methods.
Hopefully, I have provided information
about some of the biological characteristics of this parasite
and clear instructions on the most common cures. In the second
part of this series, I hope to discuss some of the newer and/or
more experimental treatments that have been proposed or recently
appeared in the aquarium marketplace. Please keep in mind
the life cycle and accepted cures for this disease in the
context of discussing the second group of treatments in part
two of this series. In many cases it is difficult to separate
an allegedly observed "cure" from simple variations
in individuals' natural immunity.
I would like to thank Eric Borneman, Adam
Cesnales, moonpod, and Dr. Ron Shimek for their editorial
content and ideas. Their suggestions were quite helpful in
crafting this two-part series.
to Part II