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Amyloodinium ocellatum, more commonly
known as Marine Velvet, is one of the most frequently encountered
pathogens affecting tropical marine ornamental fishes (Joshi,
2003, Michael, 2002, and Fenner),
and also presents a large problem for the food fish industry
(Cobb, Levy, & Noga, 1998, Montgomery-Brock et al, 2001,
Noga & Levy, 1995, CTSA,
Univ.
of Florida and Schwarz
& Smith). Consequently, a great deal of research has
been performed into its control and eradication. Because this
scientific research has included the study of the disease's
treatments, it is a real windfall for those of us interested
in marine ornamentals.
Amyloodinium ocellatum is a dinoflagellate.
Think of it as a type of single celled parasitic algae with
two flagella that it whips to get around, with characteristics
of both plants and animals. Its taxonomical designation is
somewhat complex; botanists have preferred to call it an algae
and in years past, zoologists have argued it is a protozoan.
Amyloodinium are now classed as dinoflagellates in
the Kingdom Protista, sort of in between plants an animals
being photosynthetic and also motile. At any rate, even though
it is no longer classified with protozoans, Amyloodinium
ocellatum has a complex lifecycle similar to that of Cryptocaryon
irritans (Saltwater Ich), Icthyopthirius multifilis
(Freshwater Ich), and species in the genus Piscinoodinium
(Freshwater Velvet).
The feeding stage of this parasite is called
a trophont. It can be found attached to the infected fish
by rhizoids, which are root-like structures that the parasites
use to penetrate, hold onto, and feed from their host. Once
the trophont matures and grows to an average diameter of approximately
80-100 micrometers (Schwarz
& Smith) to a maximum size of 350 micrometers (Noga
& Levy, 1995) (for a frame of reference, trophonts of
Cryptocaryon irritans have been measured at up to 452
µl (Colorni & Burgess, 1997)), it drops off the
host fish, encysts and forms a stage called a tomont. The
process of reproductive division then begins. One tomont divides
repeatedly until there are up to 256 waiting offspring. It
can complete this process rather quickly, in as little as
three to five days at water temperatures of 72-77ºF.
After these divisions stop, the cyst hatches and releases
tiny swarming dinospores, which are as small as 12-15 µl
in diameter. In contrast to Cryptocaryon irritans,
whose free-swimming theronts are viable for only a day or
two, these dinospores remain infective for at least six, and
possibly as long as fifteen, days.
Occasionally, a report describes the discovery
of Amyloodinium ocellatum tomonts in the stomach, intestines,
or esophagus of a fish. I want to be very clear that this
does not mean that Marine Velvet has been shown to display
a dormant phase, or that it can escape treatment by hiding
inside the body of its host. Rather, it is believed that these
tomonts developed elsewhere and were merely consumed by the
fish afterwards (Noga & Levy, 1995).
Because of its lifecycle, a general recommendation
has been to quarantine new acquisitions for 20 days to avoid
introducing the disease (Noga, 2000 and Trevor-Jones,
2004), but I would urge most hobbyists to isolate them
for a full month, with six weeks being optimal, for a number
of reasons. The first reason is for uniformity. Because it
will take at least a month to known if your new acquisition
is free of Cryptocaryon irritans, it is better to simply
get used to a long period of quarantine. Second, the signs
of this infection are not obvious and, in my opinion, most
aquarists can easily miss them. A full month or more of quarantine
should give you enough time to notice the infestation, or,
if you don't pick up on the signs, the fish will likely be
dead by the end of the quarantine period.
The signs of Marine Velvet infection are
rather subtle. Respiratory difficulties seem to be one of
the most common signs. Other signs are a decrease or a complete
loss of appetite, rubbing against objects in the aquarium,
erratic swimming behavior, and a dusty or dull velvety sheen,
from which this disease gets its common name. Amyloodinium
has shown a preference for first attacking the gill tissue
of fish (Noga & Levy, 1995 and Stoskopf, 1993), so once
it has spread to the body, I would consider the fish to be
heavily infected and perhaps beyond hope of recovery.
Having already written a two-part series
on treating Cryptocaryon irritans (Marine Ich), and
realizing that it shares many treatments with Amyloodinium
ocellatum (Marine Velvet), I won't waste time rehashing
what I have already discussed. Instead, I ask you to familiarize
yourself with my previous writings on the treatment options
for Marine Ich/Cryptocaryon irritans located here
and here.
This will permit me to delve more deeply into some of the
more interesting Amyloodinium ocellatum-specific treatments.
Treatment Option 1: Natural Immunity
As with Cryptocaryon irritans, it
has been demonstrated that fish can develop immunity to Amyloodinium
ocellatum after several non-lethal exposures, and that
this immunity can last for at least six months (Cobb, Levy,
& Noga, 1998). In one test, Tomato Clownfish (Amphiprion
frenatus) were exposed in containers once per week to
40,000 dinospores per fish for thirty minutes. Afterwards,
they were moved to separate aquaria for three days. At that
point, each fish was given a freshwater dip for three minutes
before being transferred to different recovery aquaria. Each
recovery aquarium had its copper concentration maintained
at 0.15-0.20 mg/l to cure the infestation. The fish remained
there for a week to allow them time to recover. After this,
the process was repeated again with another exposure followed
by treatment.
After fourteen days a significant number
of fish in the experiment showed an immune response, and after
twenty-eight days all but one fish in the study were completely
free of trophonts. What I found the most interesting was the
mode of defense. Immune fish remained susceptible to dinosporic
attachment, but for reasons that are unclear, the trophonts
never grew, and dropped off their hosts prematurely. It was
theorized that the fishes' immune response incorporated an
"antitrophont mechanism" by which a host fish that
had acquired immunity could "reject trophonts or at least
severely retard trophont development." The authors then
proposed, as a mode of protection for aquaculture facilities,
intentionally adding immune fish to retard the infection of
previously unexposed fish. Since both would be susceptible
to attachment, the immune fish could be used as a sort of
decoy, to decrease the total dinospore count in the environment.
This would hopefully subject the non-immune fish to a non-lethal
challenge of dinospores, and give those fish more time to
develop resistance to the parasite.
The last interesting observation arising
from this study concerned immunity specificity. While the
authors did not intentionally perform any experiments to test
whether this immune response would work only against Amyloodinium
ocellatum, they did have an unexpected outbreak of Cryptocaryon
irritans, which killed both unexposed and resistant fish.
This suggests that any acquired immunity is parasite-specific.
This should be a wakeup call to those of you who have still
not come around to the necessity of quarantine and preventive
treatment. It is better to be safe than sorry, and even professionals
with years of training in fish pathology sometimes make mistakes
in selecting allegedly healthy fishes. Quarantine, quarantine,
quarantine!
While it may appear that natural immunity
is the solution to this disease, I would definitely not rely
on it. Many times I have read on various message boards that
disease problems are related to stress, and therefore if we
get rid of the stressors, the fishes' own immune system will
take care of the infection. The admonition goes something
like, "Feed an excellent diet and maintain optimum water
quality, and your problems will go away." My experience
has shown, unfortunately, that not taking a quick, proactive
stance with treatment will usually doom your fish. In my experience,
Amyloodinium ocellatum has always been quick-acting
and lethal without early detection and treatment. Waiting
for natural immunity to work would be futile, in my opinion.
Remember that in the testing the fishes were repeatedly exposed
and then cured by using freshwater dips and copper. And, that
it was not until after multiple exposures and subsequent treatments
that the immunity finally gave the test subjects full protection.
Plus, we are talking about parasites here. All the stress
in the world cannot make a parasite appear out of thin air.
It would be like saying that if you have stress in your life,
you will spontaneously develop tapeworms. That does not make
sense, and neither does a similar argument regarding fish
and their parasites.
Treatment Option 2: Copper
Copper is widely available, inexpensive,
and has been proven effective. These attributes have made
it the most commonly used chemical treatment for this parasite
in the United States (Noga, 2000, Trevor-Jones,
2004, and Univ.
of Florida). But, for all its positives, copper can be
problematic. It has a narrow range of effectiveness; too high
and it can be lethal to the fish, too low and it is useless.
It requires daily, or in some instances twice daily, testing
and adjustment of the concentration to maintain the appropriate
amount, making it a labor-intensive prospect. Still, though,
it is cheap, it works, and it can be found in just about any
fish store, so it is likely to be the treatment of choice
for some time.
Treatment Option 3: Chloroquine diphosphate
Chloroquine diphosphate is a safe and proven
effective treatment for Amyloodinium ocellatum. A single
dose of 5-10 mg/l will render a fish clean of infestation
in ten days (Noga & Levy, 1995). Sounds great, but it
too has its drawbacks. First, it is hard to find. I know of
only one company that markets this drug for the aquarium industry,
Aquatronic's Marex. And while it is reported to be safe for
fishes, it is "highly toxic to micro- and macroalgae
and to various invertebrates" (Noga & Levy, 1995).
So this is yet another effective treatment that, like copper,
cannot be administered in a display tank.
Have I mentioned lately the importance
of having and using an appropriate quarantine tank? Get one
and use it. Poor ATJ, SAT, oama, and the others who are active
in the Fish
Disease Forum of Reef Central must be going insane answering
the daily onslaught of threads there. I know I rarely read
the threads there because it is so frustrating and disheartening.
They usually go something like this, "I did exactly what
every authority in this hobby says not to do. I threw this
brand new fish into my tank without a quarantine period. But,
he appeared fine to me and I have been keeping marine fish
for six whole months now. Plus, the salesperson that sold
me the fish assured me that it was healthy and he would not
mislead me just to make a buck and get rid of a sick fish.
Now all my fish are sick and dying. I don't have a quarantine
tank and even if I did I could not possibly catch and remove
all my fishes for treatment without tearing apart my whole
aquarium. What should I do now? Please help me! I don't want
to lose all my fishes!" If quarantine tanks were a standard
in this hobby, we would not have nearly as many livestock
losses, and subsequently people giving up aquarium keeping
every year.
Treatment Option 4: Freshwater Dips
A freshwater dip lasting five minutes has
been shown to force the dislodgement of most, although not
all, of the trophonts on an infected fish (Noga, 2000 and
Noga & Levy, 1995). The problem with freshwater dips is
they do nothing about encysted tomonts and swarming dinospores
already existing in the infested aquarium. Even if you lucked
out and your one freshwater dip was 100% effective, that fish
would become infected again upon reintroduction to the infested
aquarium.
Even though they are not completely effective,
freshwater dips can still be useful. For one thing, they can
be used to give an infected fish some immediate comfort by
eliminating some of its parasites prior to using another treatment
option to affect a complete cure. Also, freshwater dips can
be an effective tool for properly diagnosing an Amyloodinium
ocellatum infection. A detailed a protocol for properly identifying
Marine Velvet using freshwater dips is found here.
It is also possible to employ a freshwater dip as a cure in
and of itself (Montgomery-Brock et al, 2001). Merely give
the infected fish a proper freshwater dip lasting at least
five minutes, and then transfer that fish to a new, clean
tank. Repeat this procedure every three days, a total of three
times. At the end of this course of treatment, the fish should
be clear and free of parasites. I have to say that I am reluctant
to even mention this protocol. While it can work, it would
be extremely stressful to the fish, in my opinion. In this
case, I would have to say the cure is almost as bad as the
disease. However, that is not too say that I believe freshwater
dips are too stressful to be of merit. I do use and recommend
freshwater dips as a diagnostic tool as mentioned above and
to provide immediate relief to infected fish. I just prefer
to not use them repeatedly to affect a cure.
Treatment Option 5: Formalin
Formalin, a solution of formaldehyde gas
in water, is a controversial treatment for Amyloodinium
ocellatum. Some studies have shown formalin to force the
dislodgement of trophonts from test fish, allowing them to
be transferred to a clean aquarium free of infestation (Paperna,
1980 and Paperna, 1984). This is similar to the use of freshwater
dips and tank transfers in the above treatment option. Formalin
at 150 or 200 ppm will cause complete dislodgement in six
hours. It will also work at 100 ppm given nine hours of exposure.
But, if the fish is administered a formalin bath and then
is returned to the same infested aquarium, they will become
reinfected readily.
Given a choice between the two, I would
prefer freshwater dips. For one thing, you do not have to
run out to the local fish store to track down formalin. With
a freshwater dip, dechlorinated water and buffer, items that
should be readily on hand to any aquarist, are all that are
necessary. Plus, formalin is a rather nasty compound. It has
been shown to cause cancer in laboratory experiments with
rats, and can cause lung damage in humans (Noga, 2000). That
is why it is commonly recommended to use formalin only in
well-ventilated areas.
Formalin has a rather strange range of
effectiveness with regard to the various stages of the lifecycle
of Amyloodinium ocellatum. It can force trophonts to
drop off their hosts, but does not stop them from forming
tomonts. At a concentration of 200 ppm, it can temporarily
inhibit division and formation of dinospores, but reproduction
will begin again if the formalin is removed. It is, subsequently,
not that useful against the encysted tomonts, but effective
again against the dinospores once they hatch (Noga, 2000).
As an alternative to the bath and transfer method, one could
maintain the formalin exposure until all trophonts and tomonts
have formed dinospores, but that would require even further
exposure of the infected fish and the aquarist to this drug.
Treatment Option 6: Hyposalinity
While hyposalinity is a frequently recommended
treatment for Marine Ich/Cryptocaryon irritans, against
Marine Velvet/Amyloodinium ocellatum it is unlikely
to be useful. Amyloodinium ocellatum can survive a
much wider range of environments than can Cryptocaryon
irritans. A salinity of 16 ppt for 28 days is usually
recommended to kill Cryptocaryon irritans (Noga, 2000),
but Amyloodinium ocellatum has been found in salinities
ranging from 3 to 45 ppt (Noga, 2000), with its optimum range
of salinity for reproduction at 16.7 to 28.5 ppt (Univ.
of Florida). Clearly, lowering the salinity is not going
to be effective.
I want to leave the reader with one short
note on the use of hyposalinity for combating Cryptocaryon
irritans before I continue. Hyposalinity has been extremely
effective against Cryptocaryon irritans and likely
will continue to be for some time. But, recent research has
suggested that the salinity range of that parasite has expanded.
I would suggest reading Terry Bartelme's article here
regarding the adaptability of the parasite Cryptocaryon
irritans in certain locales.
Treatment Option 7: Acriflavin, Aminoacridine,
and Formalin Combination Therapy
This is one of the more recent medications
to enter the marketplace. Its claim to fame is that it is
allegedly a reef-safe alternative. In fact, the label on the
back of the bottle uses the term "reef safe" and
then goes on to state, "Safe for all fish (including
scaleless fish), plants, corals, and invertebrates. Will not
affect biofiltration." The active ingredients are listed
as acriflavine, aminoacridine, and formalin. Let's discuss
these in order.
Acriflavin does work against some bacterial,
fungal, and parasitic infections (Noga, 2000). I even found
reference to Acriflavin at a concentration of 6 ppm working
against reproduction in tomonts (Paperna, 1984). That is the
plus side. The downside is it is reportedly not as effective
as other agents against any kind of infection, be it bacterial,
fungal, or parasitic (Noga, 2000). It also discolors the water,
which is particularly problematic in a reef tank with photosynthetic
organisms requiring light to produce energy, and it can be
toxic to some fish (Gratzek et al, 1992). Its potential toxicity
to some fish does not bode well for its use in a complex ecosystem
such as a mature reef aquarium. Along with that, its broad-spectrum
nature (i.e., it can kill some bacteria, fungi, and parasites)
concerns me with its use in a reef display.
I was unable to find much information regarding
treating fish disease with Aminoacridine. It was one of the
ingredients of Tetra's now discontinued Oomed, which was claimed
to work against Amyloodinium ocellatum. Other than
that, I found a lot of disturbing information in various scientific
papers concerning the use of this drug as a mutagen (Medical
Dictionary Online and SCIRUS).
Furthermore, in talks with Anthony Calfo about Oomed, he recalled
some concern when Oomed was available regarding its Aminoacridine
component. He related to me the apprehension that was expressed
to him, in a fish pathology course for aquarists at the University
of Georgia, about Aminoacridine potentially lowering a fishes'
chance of reproductive success. This was specifically with
regard to the commercial breeding of freshwater Angelfish
and Discus (Pterophyllum scalare and Symphysodon
species respectively), so I am unsure how it would relate
to saltwater fishes and invertebrates, but it is something
that should give you pause.
Last is the formalin factor. In treatment
option 4 I discussed formalin's limited effectiveness against
Amyloodinium ocellatum. Formalin is, however, reported
to be toxic to algae and macrophytes/plants (Noga, 2000),
which in my mind definitely brings into question its use in
a reef tank.
Before I would feel comfortable using this
combination therapy in my reef, I would need to see documented
proof of its effectiveness against Amyloodinium ocellatum
and, more importantly, toxicology test results ensuring that
it was safe for the inhabitants of my aquarium. I was unable
to find either. If anyone knows of any data, please feel free
to post in my author's forum. I would be pleased to see it.
Until such time, I know I will not be using it.
Treatment Option 8: Ascorbic Acid
This is yet another medication which claims
to be a reef-safe cure for Marine Velvet. The packaging states
(Please bear with me as the manufacturer has a rather poor
translation from German to English and is still using the
old name of Oodinium for this parasite), "Eliminates
for oodinium in salt water. Safe with invertebrates and algae.
For best results complete the treatment program. Remove carbon
and other chemical filters. Mechanically filter over floss
or a sponge. Do not use ozone or UV sterilizers or protein
skimmer. Nitrifying bacteria will not be harmed but will be
repressed. After treatment undertake a partial water change
and use Axxxxxxx Bxxxxx to re-invigorate the nitrifying bacteria."
The bottle also labels the active ingredient as ascorbic acid.
If you don't know what ascorbic acid is, perhaps you may have
heard of it by a more common name, Vitamin C. I was unable
to find any reference to using ascorbic acid or Vitamin C
to combat Amyloodinium ocellatum in any of the articles
or fish texts that I have read. In the absence of documented,
scientific studies confirming the effectiveness of this treatment,
I am leery of recommending its use. It is possible that I
missed some study confirming its validity, so if anyone knows
of one, let me know in my author's forum. Until such time,
I cannot recommend its use.
Treatment Option 9: Ultraviolet Sterilization
Ultraviolet radiation can kill the infectious,
free-swimming dinospores of Amyloodinium ocellatum
(Noga, 2000), but its use as a cure here has the same drawbacks
as when used against Cryptocaryon irritans. Please
see here
for that discussion if you so desire. Suffice it to say that
UV devices can be useful in controlling the spread of disease
from tank to tank in commercial settings that use a central
filtration system, but are unlikely to affect a cure or even
control the spread of the parasites from fish to fish in a
display aquarium.
Treatment Option 10: Ozone
I don't have a lot to say about ozone.
It is similar to UV, as most people who use it for disease
cure and prevention, are using it as a sterilizer. In my opinion,
however, it maybe slightly more effective than a UV sterilizer
because ozone does not present as many maintenance issues
as UV sterilizers do, such as the decreasing effectiveness
seen as the UV lamp ages, or as a film develops on the quartz
sleeve and blocks the UV light from penetrating and treating
the water flowing through the unit. With an ozone generator
teamed to an ORP monitor or controller, the user will be able
to track the effectiveness of the ozone. Suffice to say, ozone
can be employed to control the spread of the disease from
aquarium to aquarium on a central filtration system, but I
would not count on it to affect a cure in a display tank.
Treatment Option 11: Biological Controls
While it is a commonly held belief in aquarium
circles that various cleaner organisms, namely Labroides
wrasses, Elacatinus (formerly Gobiosoma) gobies, and
Lysmata shrimp, can help cure diseases such as Cryptocaryon
irritans and Amyloodinium ocellatum, that belief
is unfounded. Though I discussed this in more detail in my
articles on treating Marine Ich, I will state the highlights
again here. Neither Cryptocaryon irritans nor Amyloodinium
ocellatum is routinely found in the wild, and it stands
to reason that no cleaner organism would evolve to feed on
a parasite that was rarely available. Plus, it has been shown
that Elacatinus gobies and Labroides wrasses
feed almost exclusively on gnathid isopods in the wild, so
the chances of them being useful in combating common aquarium
pathogens is unlikely. Also, cleaner fishes are just as susceptible
to infection as are the fish they are alleged to be helping.
One of the first signs of an infected fish is loss of appetite,
which would render sick cleaners useless.
Treatment Option 12: Hydrogen Peroxide
This is one of the newest ideas for treating
Amyloodinium ocellatum and, in my mind, one of the
most interesting and promising as well. The first study used
20 juvenile Pacific Threadfin (Polydactylus sexfilis)
suffering with an infection of Amyloodinium ocellatum.
They were randomly divided into four open water tanks. One
tank was the control and received no treatment. The control
fish were examined and found to have a mean of 16.6 ±
16.2 trophonts per gill biopsy. The fish that were to be treated
with varying levels of hydrogen peroxide were also examined
and found to harbor a mean of 35.6 ± 38.7 trophonts
per gill biopsy. Water flow to the three treatment tanks was
stopped and they were dosed with hydrogen peroxide at concentrations
of 75, 150, and 300 ppm. The fish were exposed for thirty
minutes and then the water flow was returned to rid the tanks
of the hydrogen peroxide. Within one hour of treatment, all
the fish exposed to 300 ppm hydrogen peroxide had perished,
but the fish exposed to only 75 and 150 ppm tolerated the
treatment without any deaths. The surviving fish were examined
immediately after treatment and found to harbor no more parasites.
They were re-examined the following day. The treated fish
were still infection free while the untreated fish were found
to have an increase in the trophonts counted.
Another test was set up at the facility
where the sick fish were obtained. Scientists used a grow
out tank that contained fish infected at a rate of 16.3 ±
13.0 trophonts per gill biopsy. These fish were exposed to
75 ppm hydrogen peroxide for thirty minutes. One day after
exposure, the trophonts' count dropped to 4.7 ± 0.6.
After six days, the count was down to 1.0 ± 1.0. At
this point, the fish were retreated with 75 ppm hydrogen peroxide
for another thirty minutes. The day after the second treatment,
no trophonts could be found. Because the study's participants
were unsure of the effect of hydrogen peroxide against tomonts,
they transferred the fish to a clean tank at this time.
Some of these same people then prepared
an experiment on Mullet (Mugil cephalus) fry. They
first studied hydrogen peroxide's effect on healthy fish.
Three groups of ten healthy fish were exposed to 75, 50, and
25 ppm hydrogen peroxide for thirty minutes. After 24 hours,
the survival rates were 20, 50, and 70% respectively. They
then decided to test 25 ppm hydrogen peroxide on a large larvae-rearing
tank. This tank held 3000 liters of water and approximately
three fish per liter. The facility had been experiencing 200-1000
deaths per day from Amyloodinium ocellatum for one
week prior to the test in this vessel, while the standard
daily mortality should have been 0.002%. The fish were treated
for 30 minutes with 25 ppm hydrogen peroxide. Within three
days of the exposure, mortality dropped to less than 10 per
day.
Now before you all go running off to the
medicine cabinet, please remember that this treatment is experimental
at best. It can easily be overdosed and cause mass mortalities.
I would wait until further research has been performed to
test the tolerance of various marine ornamentals to hydrogen
peroxide exposure. Just to be clear, I am not currently recommending
the use of hydrogen peroxide. If you choose to experiment
and use it, you could very well be risking the lives of every
inhabitant in your aquarium. I mention it only because it
is promising, and as something to keep an eye out for in the
future, after additional testing has been done. If you wipe
out your aquarium with this treatment, don't come crying to
me later.
Treatment Option 13: Flushing and Near Darkness
Flushing is a term used to describe a procedure
utilized in the aquaculture of food fish when a parasitic
disease strikes an open water system. It is simply the effort
to turnover the tank's water fast enough to interrupt the
lifecycle of the parasites. Put another way, they try to blow
the parasites out to sea while not attached to the fish. This
strategy is moderately successful at best. The reasons are
quite simple. The number of free-swimming dinospores in the
water column is diluted with each water exchange, but they
are just that, diluted. There are still enough of them of
continue to infect and reproduce. Additionally, even as they
are being diluted, they continue to reproduce and multiply.
You may think this could be remedied with a higher turnover
rate, but it remains impossible to change 100% of the water
(and dinospores) in this manner. Escobal's "Aquatic System
Engineering" gives an excellent explanation of the reasoning
behind this if you wish to view the math behind this statement.
So, why is this method used in the first
place? Well for one, it is convenient and easy. Fresh seawater
is already being pumped in to maintain water quality; merely
increasing the rate of exchange to try to flush out parasites
is a simple matter of turning up the pumps. Also, attempting
a chemotherapeutic treatment would be difficult with an open
system because of the constant dilution of the chemical agent.
So, is this method likely to be a total
failure? No, not really. Some research has suggested modifying
this technique for greater success, and this is the real reason
I wanted to discuss it (Montgomery-Brock & Brock, 2001).
In experiments with Pacific Threadfin in Hawaii, scientists
tried the flushing technique, but with one change: covering
the fish raceways to reduce the light level to near total
darkness. The idea behind this was that the low light conditions
would be unfavorable to algae. This in turn would rob the
tomonts of an appropriate substrate to adhere to, leaving
them with nothing to grasp but the bare walls of the raceways,
thereby facilitating flushing them out to sea.
The first test used 26 mildly infected
fish obtained from a fish farm experiencing difficulties with
Amyloodinium ocellatum. These subjects were divided
into two equal groups. The fish kept exposed to sunlight showed
an increase in trophont counts, while the fish kept in the
dark saw their counts decrease. After this trial, the farm
with the troubles covered several of its raceways and those
too had a dramatic decrease in mortalities compared to lit
vessels. Subsequently, this farm covered all its livestock
and has operated for over one year since without an outbreak
of Amyloodinium ocellatum.
The reason I wanted to relate this story
is to expand upon an idea I advocated in my first article
on Cryptocaryon irritans, with regard to quarantining
livestock. I prefer to use bare bottom tanks and daily water
changes for all new fish upon their first arrival. This eases
cleaning, but was also shown to be inhospitable to the tomonts
of Cryptocaryon irritans. The research above lends
additional strength to the argument for employing an unnatural
environment, such as a bare bottom glass aquarium, for quarantine
to decrease the likelihood of disease. This also runs counter
to the belief that the supposed magical healing properties
of a beautiful, healthy, natural display tank can cure even
a suspect fish. In reality, such a tank really offers the
parasites a near perfect place to reproduce; plenty of appropriate
substrate to adhere to and a plethora of potential hosts confined
in a relatively small body of water.
While some people point to the sheer number
of filter feeding organisms in a mature reef display and argue
that they are very efficient and effective predators on a
wide variety of plankton, which would include the intermediate,
free-swimming stages of fish parasites, experience has shown
time and time again that this is not a reliable solution.
While bringing home a suspect animal and placing it in an
otherwise healthy aquarium works sometimes, it is just as
likely to not work and infect the entire tank. I would argue
that in many of the instances where this appears to work,
that it is just as possible that the sick fish has been exposed
and cured of the parasite numerous times during the chain
of custody. In commercial settings with a constant influx
of new animals, it is routine to have outbreaks that need
to be dealt with. If this happens several times to a particular
fish while making its way from the reef to your reef, it would
eventually build up immunity. It is quite likely that some
of these hobbyists reporting a sick fish coming around after
being added to their display are nothing more than instances
where natural acquired immunity has finally kicked in. In
this scenario, the health, or lack thereof, of the final holding
vessel would be irrelevant. It would merely be a matter of
time, exposure, and treatments by someone else that saved
the fish and not the expertise of the hobbyist or the overall
health of their display.
Note that while Amyloodinium ocellatum
is a dinoflagellate, related to algae, the researchers concluded
that the parasites were incapable of photosynthesis and that
the lack of sunlight did not have any direct effect on the
parasite (Montgomery-Brock pers. comm.).
Conclusion:
Hopefully, I have sufficiently covered
the treatment options available for dealing with this parasite.
I strongly urge aquarists to take a proactive stance. Be strict
and quarantine all new additions for at least one month, preferably
longer. Keep a close eye out for the subtle signs of this
infection. And lastly, be prepared to act quickly with a proven
treatment if the presence of this pathogen is suspected in
your tank. At this time, only copper and chloroquine diphosphate
have been proven effective and safe sufficiently for me to
use and recommend. I am hopeful hydrogen peroxide will be
further studied, as I believe it has the most potential for
a reef-safe treatment option, but additional experimentation
is needed.
Acknowledgements:
I'd like to take a moment to thank Anthony Calfo, Robert
Fenner, Dr. Ron Shimek, and Andrew Trevor-Jones for their
editorial advice and content.
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