Columnaris is a disease caused by the bacteria Flexibacter columnaris, a long, thin, rod shaped
motile (capable of movement) bacteria. The bacterial clumps form microscopic columns or
dome shaped masses, hence the name columnaris. Two years ago I rarely read about this disease
on fish forums, now it is getting more and more common.
Symptoms: Symptoms of this disease include grayish-white spots on some part of the head, fins,
gills, or body usually surrounded by an area with a reddish tinge. The columnaris lesions on
different species of fish vary in size, location, and appearance. These may appear thread-like, particularly
around the mouth, giving rise to the incorrect name of 'mouth fungus'. Characteristic lesions
can appear on the back, the fins, gills and belly. Catfish, in particular, tend to have lesions
on their bellies and sides. Fins will deteriorate and sores may appear on the body. The gills may
be affected, giving rise to bacterial gill disease. It may cause 'shimmying' behaviour in fishes,
particularly livebearers. Mollies, for some reason, seem to be particularly susceptable. Although
columnaris most commonly involves external infections it can occur as an internal systemic infection
with no visible external signs.
Columnaris is often mistaken for fungus, as most of us are taught that white fuzzy growth on the
skin of a fish means fungus. However, white or grayish white, fuzzy looking lesions on that occur
on normal skin, mouth or fins - especially with a bleaching of the skin underneath - fish are much
more likely due to columnaris. True fungus generally grows on infected wounds or torn fins, that is,
it grows on dead tissue.
Causes and Course of Disease: Columnaris is opportunistic and strikes when a fish is stressed.
Poor water quality, sudden changes in conditions, wide temperature swings, high nitrate concentrations,
low dissolved oxygen concentration, crowding, shipping, and bullying can also trigger columnaris.
Columnaris will be more virulent in temperatures above 77 degrees. My LFS tells me that summertime
is "prime time" for this disease and they almost always suffer significant losses when fish are
shipped in warmer weather. Hard water with a high Ph seems to accelerate the course.
Under appropriate conditions columnaris can spread rapidly and cause catastrophic losses.
One strain has a virulence that is low and it takes a few days to kill the fish. On the
other hand, the highly virulent strain will kill a fish in under 24 hours. If your fish
has the highly virulent strain, there is not much that you can do to stop it or treat it.
These fish often die so quickly that there may not even be enough time for them to show
any external signs of infection.
Treatment: First, slowly lower the temperature in the tank to 75 or 76 to slow the course of
the disease. Also, since columnaris thrives in low oxygen conditions, the addition of an
airstone or lowering the water level to create more splash from the filter will also help.
The most effective treatment for columnaris if the fish is still eating is medicated food
containing oxytetracycline. Aquatronics makes such a food, as does Zeigler. Often, however,
the fish is not eating by the time symptoms are noticed. Antibiotics in the water would
be the next treatment option. Erythromycin (Maracyn), nitrofurazone, nifurpirinol,
acriflavine, chloramphenicol or tetracycline can be used to treat the columnaris itself.
However, a fish infected with columnaris often falls prey to a secondary infection
which is resistant to both of these. Therefore, a combination of Maracyn and Maracyn
Two or tetracycling and kanamycin is recommended. CONTINUE TREATMENT FOR A MINIMUM OF
10 DAYS.
I should note here that resistant strains of columnaris are cropping up on both sides of the
Atlantic. We currently have nothing that will treat it. Strict quarantine measures should be
maintained with ALL new fish. It's hard enough to lose a new fish, but to lose old friends is
somehow worse.
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