Pox on Carp
The likelihood of koi
having carp pox is rather,
By Stephen M. Meyer
Carp pox was probably
the earliest recognized
viral disease of fish. It
was discovered about
400 years ago. Carp
pox is actually a herpes
virus: herpes virus
cyprini. Macroscopically, it produces whitish, opalescent, very hard bumps on
the external surface of the fish — signs very similar to those produced by
about two dozen other common fish diseases. Thus, only a virological
analysis can determine the presence of carp pox.
While it is possible that your fish do harbor this virus, I can almost guarantee
that your fish do not have "carp pox." It's just not that common among
ornamental carp. In fact, I have never seen a properly diagnosed case of carp
pox on any koi and have only heard of a handful of authenticated cases.
Unfortunately, many well-meaning hobbyist "koi doctors" (and hobbyist
books) have also been misled by the appearance of large, opalescent
bumps into the misdiagnosis of a much more common problem: coldwater
"ich" parasite infestations. This parasitic disease is very commonly seen in
the eastern and northern parts of the U.S. and it can be a serious threat to the
fish, especially to young koi.
Coldwater ich disease (an infestation of the common Ichthyophthirius
multifilis parasite) usually occurs as water temperatures warm to the range of
10 to 15 degrees Celsius (50 to 60 degrees Fahrenheit). As a result,
coldwater ich is most often seen in early spring. However, careful
examination will reveal its presence on fish in colder mid-winter waters as
well. It also appears when water conditions are poor.
The signs of an infestation are large, wax-like bumps on the fish's scales, fins
and around the mouth — noticeably different in size and shape from the far
better-known "salt" spots caused by ich in warm water conditions.
The bumps produced by coldwater ich may be whitish, grayish, bluish or
pinkish in color. These bumps are not the parasite but a reaction of the fish's
outer skin to the parasite burrowing into the flesh. Ich-related bumps can
often be scraped away with a fingernail (though this is NOT recommended),
whereas true carp pox growths cannot be scraped off.
Thus, in terms of both the conditions that produce the disease and their
macro-appearance, carp pox and coldwater ich are indistinguishable even to
the advanced koi keeper. The difference is that the latter can be treated
The disease can indeed be "cured," but it requires gradually warming up the
water and the fish to temperatures of about 20 degrees Celsius (68 degrees
Fahrenheit). At this temperature the disease does not disappear, as some
pondkeepers assume — it merely becomes less noticeable because the
spots shrink. Once the water temperature reaches approximately 20 degrees
Celsius, standard ich treatment with malachite green/formalin can rid the fish
of this parasite. This treatment, however, requires maintaining the higher
backyard pond temperature for a couple of weeks.
Because Ichthyophthirius multifilis is a ubiquitous parasite in a koi pond,
there is no way to get rid of it. It can only be controlled. Maintaining excellent
water quality is essential. By keeping water conditions at the optimum pH,
with plenty of dissolved oxygen and no measurable ammonia or nitrite, the
immune systems of the fish will minimize infestations.
In other words, the single most effective way to prevent major outbreaks of
this parasitic disease is to maintain a low fish load in the backyard pond.
Good water quality and a low fish load will enable the natural defenses of the
fish to control the parasites all year round.
The same basic advice is also good for the far less likely carp pox virus.
Here again, good water quality, low fish loads and moderate water
temperatures will control the outward manifestations of the disease. This
cannot be overemphasized. Pondkeepers who adhere to this advice seldom
are troubled with diseased koi or goldfish.
*brought to you by fishchannel