Nematodes form another phylum that is divided
among harmless free-living "threadworms,"
which you may see in the biofilm or in open
water, and insidious parasites that you are
never going to spot, unless they appear at
the anus of an infested fish. Whenever you
see a fish that is wasting away, without
external wounds, lesions or external parasites
like Ich, you can generally suspect that
an internal parasite is at work, especially
a nematode worm. Ordinarily it requires infected
fish to introduce parasitic nematodes to
trouble your Eden. Quarantine will help,
if you'll allow enough time for the worms
to reveal themselves. Insect larvae, copepods
and tubificid worms have often been accused
as the first intermediate hosts of parasitic
nematodes. Whether or not these invertebrates
are involved in certain specific nematode
life cycles in natural waters, the blackworms
and tubifex at your LFS have been farmed
in water that does not have infected fishes
in it. With the cycle broken in this way,
there is no source of nematode eggs to infect
the live food organisms.
Camallanus cotti Often with the nematode Camallanus, your
first view of the parasite may be one or
several reddish worms protruding from the
fishes' anus. The worms are actually transparent;
the red tint is from the victim's blood.
The ones you see are all females, which can
get to a centimeter in length; the little
males are a third their length. At this point
the host's intestine is packed with parasites,
and the creatures are shedding their microscopic
larval young into the water.
Most species of Camallanus and its close
kin shed eggs, and their life cycle needs
an intermediate host, often a copepod or
perhaps a cladoceran (such as daphnia); their
reproduction gets disrupted in the aquarium,
though copepods are everywhere, especially
in planted tanks. But C. cotti and the less-common C. lacustris are viviparous: their larvae develop within
the adult female worm who sheds them into
the water; several successive generations
can infect aquarium fish.
The young worms are as likely to be eaten
by a copepod as by another fish, but either
way they get passed to the next fish host.
In the severest cases maybe the best thing
you can do is net out the sufferer, gently
euthanise it, and concentrate on the other
fishes that are infested but not so far gone.
Don't try to net the fish and pull off the
worms with a tweezer; they are deeply embedded
and you'll just tear the intestine wall.
Parasitic nematodes weaken the host; what
kills it usually are secondary infections.
In retrospect, you may realize that the victim
had been showing some inflammation in the
vent area and might have been passing whitish,
mucusy feces. Too often we let symptoms like
these pass unnoticed.
In the wild most fish harbor some parasitic
nematodes. Fish populations are diffuse enough
that the chances of a nematode egg being
successfully transfered are low, and besides,
a healthy fish can usually live with the
normal range of its familiar co-evolved parasites,
just as many humans harbor Giardia without
suffering significant ill effects. However,
when fish are caught and transported to exporters,
then flown from wholesaler to wholesaler,
shipped to retailers and at last to hobbyists,
they have been put through enormous stresses.
To a fish with stress-impaired resistance,
even a modestly benign and familiar parasite
may become serious. How much more lethal,
then, is an alien parasite that has not had
time to "learn" not to damage its
host.
Camallanus cotti was first described in Japan in 1927, but
has been distributed throughout the world,
largely from the fish farms of Singapore
and Malaysia, especially after 1980.
Treating for Camallanus. The best drug to eliminate intestinal nematodes
is levamisole hydrochloride (Janssen-Ortho).
You need to bring your pH down to 7.0 or
lower for this drug to be effective. In 1996
Ken Laidlaw devised the successful treatment
using a 7.5% solution at 1.5 ml/7.5 liters.
Chemist/killifish breeder Charles H. Harrison
described the pest and its successful treatment
in the Journal of the American Killifish Association, March/Apr 1998, p 57; luckily it's archived
at the AKA site. (Scroll way down for it) --or you can download
a pdf doc. version from the St. Louis Area Killifish Association website.
One commercial form of levamisole, for de-worming
pigs and sheep, is marketed as "Levacide."
Some useful notes about successfully treating
for Camallanus with a form of levamisole
hydrochloride called "Tramisole,"
a sheep de-wormer, are in anApistogramma-Mailing List thread that began 15 Dec 2000, archived at www.theKrib.com.
Be sure to follow this thread to its conclusion.
Fenbendazole is the other most-recommended
de-wormer. You soak flake feed or freeze-dried
daphnia in a solution. It's a good idea to
give the fish a fast-day first, to encourage
them not to spit it out.
Fresh garlic extracts, as used to combat
intestinal parasites like Capillaria (see below), may be effective for Camallanus.
Capillaria. Capillaria are parasitic nematodes that
are smaller than Camallanus and proportionately
very thin ("capillaria" means "hair-like").
There are numerous species, most of which
were originally from South America, where
they co-evolved with certain specific hosts.
The smaller the host, however, the more troublesome
even quite minute parasites can be; Capillaria
may be a cause of some inexplicable wasting-away
you observe in small tetras. The fish eventually
dies when a vital organ is no longer working.
When intestinal parasites get transferred
to the "wrong" host, as happens
in captive populations, they can do unaccustomed
damage.
There are two kinds of
Capillaria. Most live
rather innocuously in fish
intestines and
cause trouble only when
they become too numerous.
Their eggs are shed and
passed out with the
feces. When an egg is ingested
by another
fish, the life cycle gets
repeated. Other
Capillarian types have
alternate hosts. If
your fish is the intermediate
host and ingests
an egg, the hatched worm
bores through the
intestinal wall and makes
its way through
muscle fiber and internal
organs to encyst.
There it awaits its final,
or "definitive"
host, the one that eats
the infected fish.
Encysted capillarian worms
are untreatable,
though they won't multiply.
If the cyst is
near the skin, you might
confuse it with
a tumor or a digenetic
trematode.
Capillaria have been transmitted through
tubifex in lab experiments, according to
the ZFIN website, but the common method of transmission
in aquaria is from fish directly to another
fish.
Try treating Capillarians with Mebendazole/Trichlorfon
(Fluke Tabs, from Aquarium Products, for
instance). Trichlorfon is a brand name for
dimethyl trichloro hydroxyethyl phosphonate,
which is also the active ingredient in Clout.
Add a second treatment after ten days, as
the eggs are resistant.
Bioencapsulation is a good technique for
getting the medication into the fishes' intestines,
where it can work.
The famous Discus breeder Jack Wattley has
developed a technique to control Capillaria nematodes
in Discus using fresh-squeezed garlic in every feeding
over a period of several weeks. He published
his "garlic cure" in a book on
Discus, but it really caught on when the
technique was published in Tropical Fish Hobbyist, May 1999. A single "shot" of
garlic, or the extract merely dissolved in
the aquarium water, is useless. But stand
by (as of the winter of 2002-3) for a wave
of enthusiasm for garlic extracts to treat
all kinds of aquarium vampires.
