FISH ARTICLES: WATER MOLD INFECTION
Synonyms. Saprolegniosis, Ulcerative mycosis, Oomycetes, Cotton
mouth disease.
The most common presentation of water mold infection as as a
relatively superficial, cottony growth on the skin or gills.
Such lesions usually begin as small, focal infections that can
rapidly spread over the surface of the body. It is not
unusual for large lesions to suddenly appear within 24 hours.
New lesions are white, due to the mycella of the fungus, and over
time will become red, brown, or green as a result of trapping algae
or debris. When the fish are removed from the water they
appear to have a "slimy" matted mass growing out of the skin and
scales.
This disease will progress rapidly, producing lesions that can
form a deep, necrotic ulcer. This can extend deep into the
body and will frequently affect internal organs. After time
the infected tissue will slough off, leaving a large crater-like
hole, surrounded by dark red or white muscle.
Although typical saprolegniosis lesions grow rapidly over the
surface of the skin, they usually do not penetrate deeply into
muscle. However, the damage to the skin or gills may be enough
to kill the fish. The severity of the disease is determined by
the area of skin and gill damage. The larger the area
affected, the greater the osmotic stress and electrolyte imbalance.
Skin woulds due to net damage or other trauma increase the risk of
infection.
Many oomycetes display a seasonal re-occurrance.
Saproglenia species are seen mostly in cooler months of the year.
Most saprogleniaceous oomycetes are prevented even by moderate salt
content in the water. There is also evidence that many fungal
infections affect hosts that are "stressed".
Oomycetes infections can also be a secondary infection. If
the fish had a pre-existing bacterial infection due to a motile
aeromonad (aeromonas or hole in the side disease), the fungal
disease will surely attack the open sores.
So, basically... there are many factors which can contribute to
this disease. It is suggested to research thoroughly all
contributing factors before diagnosis is made.
Treatment and Control:
Most molds are usually inhibited by even low concentrations of
salt. Salt also helps to counteract osomotic stress in
affected fish with skin damage and salt loss. However this
treatment will not totally arrest fungal growth. High
salt concentrations are not the cure-all that many fish keepers
believe. Too much salt can actually do more harm than
good!
A formaldehyde & malachite green solution (Forma-Green) is
suggested to control algae, mold and fungal infections.
Potassium permanganate is also another good choice, but in some
cases is not effective enough to completely control this disease.
Thank You and Good Luck,
Dr. Gary Aukes; Pharm D, and the staff of National Fish
Pharmaceuticals.
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