Oodinium (Amlyoodinium)
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There are two basic forms that attach aquarium
fish, one that causes the freshwater infestation (and has more than variant),
and the other which attacks saltwater fish. We will discuss both here starting
with the freshwater form.
Oodinium pillularis.
This is the Latin name given to the parasite that causes the disease more
popularly known as Velvet, Gold Dust or Rust disease. This variant is the most
often encountered, but be aware that there are also at least a couple of other
very similar freshwater forms.
The infestation is caused by a parasitic
dinoflagellate that is variable in size, as the variants differ somewhat in
their measurements. Other forms that cause very similar signs are Oodinium
limneticum and Oodinium vastotor. These can measure more than 100
microns although the more typical sizes are 50-70 microns.
One of the greatest problems with this parasite in
both the freshwater & the saltwater form is that most typically the Hobbyist
will observe the infestation only when he sees a fish, sometimes more than one,
gasping for air and in the last stages before death.
Usually this is when the fish is laying on its side
on the bottom of the Aquarium, as it tries desperately to get air by attempting
to breathe at the surface.
At this advanced stage of
infection it is rare indeed to save the fish, however if prompt action is taken
it is possible to save other fish, as without doubt if such remedial measures
are not applied then virtually all the fish will be lost and usually within a
very short space of time.
The parasite attacks the skin of
the fish & inserts "roots" which can easily be seen under microscopic
examination. Another favorite site of attack are the gills of the fish, which so
typically then cause the most observed sign, that of "panting" for breath as
mentioned. These parasites eat into the cells of the epithelial layer, or the
sensitive tissue of the gills, and destroy them in the process. After the
parasite has matured it falls off the fish much in the manner of white spot
(Ich) in both fresh & salt water, and here it begins several stages of mitotic
division, ending up with some dozens or even more of cells which are
flagellated.
In both the free swimming
flagellated stage as well as the parasitic stage when attached to the fish, the
organism contains a form of chlorophyll. This gives the parasite its typical
gold or rust color, and also enables it to obtain food as do plants by the
process known as photosynthesis. However when in the parasitic form almost all
of its nourishment is obtained at the expense of the host, which causes
tremendous damage leading to death once the fish is heavily parasitized. On the
fish the dinoflagellate form grows in size about 5-6 times, before falling of
and replicating itself in the free swimming form.
These flagellated free swimming
forms are in fact dinoflagellates which must, within the space of one day, find
another fish to infect or they will die. The relatively short life cycle &
massive reproductive capacity ensure that if an outbreak occurs and it is not
treated, heavy losses will follow. Fortunately it is not too common, but has no
equal in the speed in which it can cause havoc in any aquarium unfortunate
enough to have an outbreak. Sometimes a few fish will survive an outbreak for
reasons that are not entirely clear, and these usually have developed an
immunity of some form to the parasite.
Younger fish appear to be much more susceptible to
the parasite, perhaps because they have a less well developed immune system. If
young fish become exposed the casualties will almost invariably be much higher.
However, if untreated, even adult fish will succumb.
Typical signs of
infection.
Oodinium pillularis & related species.
Water.
Without any doubt, less than ideal water quality is one sure way to help in
the outbreak of any parasitic infection, and in this respect Oodinium is
no exception. However the primary reason for its introduction is usually to be
found elsewhere in this instance.
Behavior. Gasping for air,
with very rapid respiration, most typically on the floor of the Aquarium, but
sometimes at the surface, is nearly always observed. In the early stages of an
infection, "flashing" or rubbing & scratching are often indications, as the fish
tries without success to rub off the irritating organisms.
Fins. Fins can become
clamped and folded.
Body. The most observed
feature of this infestation is a salt & pepper effect of hundreds of small
dots, usually with a cast of gold/yellow or rust color, which give the
appearance that the fish has been covered with a special form of talcum powder.
It is sometimes difficult to see this unless the light is coming from the back,
and shines off the fish, when it can easily be seen. This advanced phase of
infestation is however almost always fatal, and the hobbyist should try to
become aware of the earlier signs if he/she wishes to be able to take meaningful
action.
Gills. Excessive mucous
will be a sign that the parasite is attacking the gills, and a smear should
easily confirm this.
Skin. The skin becomes
"dusted" with hundreds of small raised parasites, giving a color which according
to the variant of the form encountered will be from a yellow gold color to an
almost red shade.
Prognosis. As already
stated, if the problem is only discovered when the parasite has made large
inroads into many fish, then severe casualties are to be anticipated. Older fish
of certain species often will resist the infection, though they will also
succumb in many instances if no action is taken. Young fish typically will die
like flies, if they are not helped with appropriate action by the Aquarist.
However if a suitable remedial regimen is introduced, excellent results can be
expected.
Treatment.
There are several treatment
options that can be employed including raising the temperature or the addition
of Copper Sulphate.
Raising
the temperature by some 8 - 10 degrees Fahrenheit, to about 86°F can be
effective BUT is also dangerous. The higher the temperature, the lower the
dissolved oxygen content; not an ideal situation for an already stressed fish.
Copper
Sulphate treatment is widely referred to in the literature, but has to be used
with extreme care, as many fish are highly susceptible to Copper, and vary
species by species in the toleration of it. Furthermore the hardness or
otherwise of the water plays a critical role in the effect of the Copper. If it
is not hard enough then no benefit will ensue. In addition, Copper levels tend
to drop and must be monitored frequently if good results are to be expected.
This is often just not practical for the average hobbyist who has to work during
the day.The treatment of choice is an Acriflavine drug used
in combination with other chemicals. This combination gives excellent results
(Our products, Revive and
Aqua Pro-Cure, are just such a combination treatment). Do not use any
carbon during treatment & subdued lighting is recommended. We have found over
many years of experience, that while no drug is perfect, Acriflavine or some of
its close relatives give an excellent result with minimal effect on the fish.
After treatment carbon should be used in the filter to remove any residual
"green/yellow" cast to the water.
Salt Water Coral Fish Disease.
Amyloodinium ocellatum aka
Oodinium ocellatum.
This is the
form of the parasite that gives rise to the disease known as Coral Fish Disease.
There are many similarities between this marine variant of the parasite and the
fresh water forms.
So that the salt water Hobbyist should be take into
the account the differences and not make an error in diagnosis let’s discuss
some of the special features of the salt water form.
In the fresh water forms O. pillularis & O. limneticum
, the organism's primarily attack the skin, & then spread to the gills. In the
saltwater form O. ocellatum the parasite seeks out the gills & may then spread
to the skin.
By the time the latter takes place however, the gill
damage is almost invariably so severe, that the typical "first alert" I have
already mentioned of seeing a fish "gasping" on the bottom of the tank, is
unfortunately all too common. The parasites damage the gills, causing
hemorrhaging, swelling, and intense necrosis, which lead to an inability of the
fishes’ gills to pass sufficient oxygen, which leads to suffocation & death.
The
reproductive phase of the free swimming dinoflagellate takes place optimally in
water of a pH of 8.0- 8.2 with a density of 1.012- 1.021 and with a higher than
desirable organic load, especially of Nitrate.
Typical signs of infection. Oodinium ocellatum
Water.
High organic load, with less than optimum water conditions, can often serve
as the precursor for an outbreak. It thrives in temperatures of 77-86 F., and
salinity of 1.012-1.021.
Behavior. Gasping for air, with very rapid
respiration, most typically on the floor of the Aquarium, but sometimes at the
surface, are nearly always observed. In the early stages of an infection,
"flashing" or rubbing & scratching are often indications as the fish tries
without success to rub off the irritating organism. If the hobbyist can pick up
this "flashing" action at an early enough stage there is a chance he /she can
prevent mortality.
Gills. Excessive mucous will be a sign that the
parasite is attacking the gills, and a smear should easily confirm this. Heavy
necrotic damage is easily observed even with a good hand magnifier.
Skin. The skin will show "gray" patches which
if examined closely will manifest a "dust like" appearance, giving the skin a
"velvet" look, which has given rise to an alternative name for the disease. Some
hemorrhaging may also become evident.
Prognosis. The disease as with its freshwater
counterpart, usually comes to the attention of the hobbyist with the first fish
or more, giving their last gasps as said on the bottom of the tank. At this
stage seldom can such fish be saved and the outlook for them is very poor. If
however there are still large numbers of uninfected fish, or some only lightly
infested, then if prompt and suitable action is taken, it should be possible to
save the others.
Treatment. The remedy for the saltwater form is
rather difficult. Copper has often been indicated as a drug of choice, but has
many problems in its use, as well as been dangerous to the fish in even small
overdoses, and especially if even minor damage has already occurred to the gills
of the fish. In Reef tanks it cannot even be considered.
Methylene blue, has been used with some
success, as it has the advantage of been an excellent oxygen transporter, which
aids the transpiration of oxygen to the fishes gills. Methylene blue however is
highly toxic to Nitrifying bacteria and its use should be confined to a separate
quarantine tank only.
Acriflavine and related compounds have
proven very effective and have given the most consistent results over the years.
(Our products, Revive and
Aqua Pro-Cure have been formulated incorporating Acriflavine and
other compounds to yield excellent results). These products can be used in both
fish only and/or reef aquariums, and will not adversely impact corals or other
invertebrates. Carbon and Protein skimmers should not be used during the
treatment period, as they pull the compounds out of the water, but should be used to clear the
tank once treatment is completed. Lighting should be subdued during the
treatment period.
In both the
fresh-water & saltwater form of the disease, the reproduction and hence the
eventual intensity of the infestation is closely related to the temperature.
Lower temperatures will slow down the reproduction of the parasite, and thus
possibly give the Hobbyist a little more time to take effective remedial action.
The Hobbyist must evaluate however the species he/she has in their tank, and the
tolerance for a lower temperature that their collection of fish, is likely to
withstand. Some
freshwater species such as white clouds will thrive in lower temperatures,
others such as Discus, will emphatically not.
Refs.
Diseases of Fish C.van Duijn Jr. P
52-56. Iliffe Books UK
Handbook of Fish diseases Ed. Dieter
Untergasser p. 89-90 TFH Publications.
Papperna I. (1980) Amyloodinium
ocellatum (Brown 1931) (Dinoflagellida) infestations in cultured marine fishes
in Eilat , Red Sea: epizootiology and pathology J.Fish Dis 3: 363-372
Noga E. (1987) Propagation in cell
culture of the dinoflagellate Amyloodinium , an ectoparasite of marine fishes
Science 236. 1302-1305.
Cheung P.J., Ruggieri G.D., and
Nigrelli R.F. (1978) Effects of temperature & salinity on the developmental
cycle of Oodinium ocellatum Brown (Mastigophore: Phytomastogophoresa:
Dinoflagellida)(abstract) The Fourth International Congress of Parasitology in
Poland.
Negrelli R.F. (1936) The morphology,
cytology, and life-history of Oodinium ocellatum, a dinoflagellate parasite on
marine fishes. Zool N.Y. 21: 129-164.
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