Fungal infections are much less prevalent in fish than bacterial
infections. Fungi in water
are usually symbiotic
with bacteria. The likelihood
is that any
microscopic investigation
of fungused areas
would show that the Saprolegnia
"fungi"
were confined to necrotic
tissue, tissue
that was already essentially
dead or dying.
Combinations of various
bacteria and fungi
are responsible for "fin
rot" and
"tail rot," for
gill necrosis and
body lesions, as well as
the cottony hyphae
of mouth "fungus."
Treatments for all these conditions are similar.
The pros always emphasize that only sick
or immunologically compromised fish are susceptible
to fungal infections. Stress from crowding,
deteriorated water conditions, unnecessary
handling or sudden drops in temperature can help lower a fishes'
resistance. Not every abrasion from being
netted, not every normal scrape or bruise
leads to fungal infection.
The commonest culprits are members of a group
of water molds collectively called Saprolegnia. Normally the Saprolegnia group are saprophytes,
which means that they make a living breaking
down organic plant and animal tissues and
even decaying wood. (Latin "Saprolegnia" is "the wood rotter.") In this
common mode of life Saprolegnia and its cousins
among the water molds are a normal part of
the biofilm and help recycle nutrients in the aquarium.
The spores of Saprolegnia are normally everywhere.
But Saprolegnia are opportunists that can
invade necrotic tissue, which is deprived
of the normal supplies of blood and lymph
that routinely carry away invading organisms
and destroy them. Though you don't see the
fungal hyphae of Saprolegnia until they appear
as a cottony growth, fungal symptoms such
as "cotton-mouth" are actually
secondary infections. They follow some primary
trauma that isn't healing fast enough to
keep ahead of germinating fungal spores.
Healthy fish are able to resist Saprolegnia
by the flow of mucus, which sweeps away spores,
and by actively inhibiting factors found
in normal mucus, until damaged tissue has
been healed.
Mouth "fungus" used to be often attributed also to "columnaris,"
a name that alludes to one species (Flavobacterium [Flexibacter] columnaris) among a group of myxobacteria that are
ever-present, both in aquaria
and in natural
waters. There is more about
"columnaris
disease" among the
bacterial infections.
Finrot (or "tailrot") is a common disease,
where the fin tissue erodes away from the
edges and the fin gets ragged or splits.
With spiny-finned fishes such as gouramis
and cichlids, the fin may recede between
the more resistant fin spines, leaving them
to protrude like the spokes of a torn umbrella.
In fin rot the eroding edge may have a whitish
cast, where bacteria are joined by oocyte
"fungi" like Saprolegnia. If the
condition is ignored, the entire fin may
rot away, and reddened areas of bacterial
inflammation and sores can even appear on
the fishes' body near the base of the fins.
Things should never get this far in an aquarium.
If you catch finrot early enough, fin tissue
regenerates within weeks to months. Fin spines
may not regenerate as well. Fins that have
eroded to the base don't usually regenerate.
Multiple causes. Newbies are often plagued by "fin-nipping,"
even in communities of mild-mannered tankmates.
I often suspect fin rot. More advanced fishkeepers
still may feel there must be some "physical"
cause for fin deterioration-- the betta has
snagged its flowing fins on a rock, etc.
I think it's just as likely that a rich load
of organics dissolved in the water has encouraged
minor ectoparasites, like Epistylis or skin flukes
(Gyrodactylus), and that the irritation they cause has
opened opportunities for bacteria and Saprolegnia.
Since rich loading of dissolved organics
encourages a dense population of flagellates
and ciliates, some of which are opportunistic
skin parasites, then the "stress and
deteriorating water quality" that are
so often invoked as "causes" of
finrot, are predisposing factors after all.
I don't think it's useful to try to isolate
"fungal" finrot from "bacterial"
finrot. "Fin rot is a bacterial disease
involving opportunistic bacteria such as
Aeromonas, Pseudomonas or Flexibacter that
abound in all aquatic environments. Secondary
fungal infections are not uncommon,"
Frank Prince-Iles tells you at www.fishdoc.co.uk. Radical approaches are possible where a
seasoned veterinarian treats large koi, but
you won't be injecting the Neon Tetras with
antibiotics.
Treatments. Whatever medication route you decide on,
the preliminary step is
sanitation. You can
do a few things to promote
rapid healing
yourself. For a start,
you'll have better
success with fungus cures
if you precede
them with a 50% water change,
after siphoning
out all loose mulm and
debris. This reduces
the dissolved organic content
of the water.
You don't want the medication
to expend itself
oxidizing organics in the
water. Follow up
a few hours later, when
the water is clear
of floating debris, with
a thorough backflushing
of the filter. And raise
the temperature
to 80°F--— not enough
to stress the fishes--—
because fungi grow more
rapidly at cooler
temperatures, which also
slow fish metabolism.
Mouth fungus or finrot
may not be directly
communicable from one fish
to another. Whether
they are or not, many of
the following treatments
for fin rot are stressful
to plants: can
you isolate the afflicted
fish in a Q tank?
You'll see anti-fungal
patent medicines and
herbal remedies at the
LFS touted to "promote
healing." Read the
ingredients of your
patent anti-fungal medication
with a critical
eye.
Anti-bacterial medications from the furan group or sulfa drugs-- even
the use of medicated feed--
and herbal tinctures are often recommended. I would look more
to basic causes, first dealing with detectable
ammonia and nitrite, increasing my sanitation
regime, diluting and oxidizing dissolved
organics, and then ridding the fishes' skin
of minor ectoparasites.
Saltbath. Long-term salt baths and a gently warmer
temperature are often all
that is needed,
if your alert eye has caught
the incipient
finrot when just the fraying
tips of fins
are showing white where
they should be clear.
The salt is particularly
effective again
Saprolegnia.
Dyes. Not all dyes are
effective. Malachite
green and formalin are
often recommended
as an anti-fungal remedy,
though they can't
be used with food fish.
Now that malachite
green has developed an
exaggerated rep for
toxicity it's sometimes
presented as "Victoria
Green".
Acriflavine is sometimes
recommended-- i.e.
at at Adelaide Aquariums. Acriflavine is a powerfully staining and
irritating dye, which you ordinarily buy
pre-mixed. Acriflavine is not a fungicide.
It will trash your plants, so if you use
it, confine it to a plant-free Q tank.
Chloramine-T. Chloramine-T is effective against bacteria
and protozoa. It is more effective and more
toxic at lower pH. If your water is already
chloraminated, you might simply try a series
of daily water changes with un-dechlorinated
water. Stand by with AmQuel ready to dose
the untreated water at any sign of increased
rates of respiration. The Provet website suggests chloramine baths at concentrations
well above what you'd normally find in your
chloramine-treated tapwater.
Phenoxyethanol. Davy Reynolds also recommends patent medications based
on phenoxyethanol.
Potassium permanganate. If you act cautiously enough, potassium
permanganate will oxidize
residual organics,
eliminate ectoparasites
and attack fungi.
It is the treatment to
try when a salt bath
is not halting fin erosion..
Links. An article by Kent Mayer, OSU Dept of Fisheries, describes
Saprolegnia and its treatment in food fish farming operations,
with links to further websites.
Dr. Beverly A. Dixon wrote about fungal diseases in Aquarium Fish, May 1991.
