BY JOHN DAWES
Everyone agrees that introduced carp pose a se- rious threat to native fauna and flora in numer- ous countries and regions. Australia is almost
certainly the best-known affected area, possibly
because, as a result of the authorities’ view on the
matter, koi do not appear on the list of live freshwater fish species whose import is permitted. Thus,
Australian hobbyists are being denied significant
access to this rewarding aquatics sector, while the
trade, too, is being denied opportunities enjoyed by
their colleagues in other parts of the world.
All this is the result of koi belonging to the same
species as the common carp (Cyprinus carpio), whose
invasive qualities are beyond doubt. In fact, the situation is so desperate that, as I reported some time
back, the Australian authorities have decided to
release the herpesvirus 3 pathogen (CyHV- 3)—the
agent that causes the deadly carp and koi herpesvirus disease—into Australian waters in an attempt to
eradicate established carp populations.
Studies carried out over a seven-year period at the
Commonwealth Scientific and Industrial Research
Organisation (CSIRO) Animal Health Laboratory
have shown that the virus is pretty effective, taking
just over a week to kill its victims. Therefore, the situation seems quite clear: Release the virus and eradicate the carp. What could be simpler?
Well, I’m sure that readers of this column know
that few things are as simple and clear-cut as this.
Aside from the daunting challenges presented by
millions of rotting carp corpses, with the plethora of
logistical and environmental complications that they
would give rise to, to say nothing of the high costs
involved in the program—estimated to be around
$18 million—there are other factors that cast doubt
on the reasoning behind the proposed virus release.
One of these relates to the actual efficacy of the
virus itself, because not all carp will die, leaving
virus-resistant survivors. Indeed, and worrying-
ly—one would assume—for the proponents of the
release, genetic polymorphism has been detected
in carp. This means that carp vary in their genetic
makeup and, thus, their response and sensibility to
external factors, which could include pathogens. In a
paper titled Genetic Evolution and Diversity of Com-
mon Carp, Cyprinus Carpio, published in the Central
European Journal of Biology in September 2009, the
authors, Dimitry Chistiakov and Natalia Voronova,
state that “Knowledge of genetic variation and pop-
ulation structure of existing strains of both farmed
and wild common carp Cyprinus carpio L. is absolute-
ly necessary for any efficient fish management and/
or conservation program.”
To what extent this has, or has not, been taken into
account by the Australian authorities is not clear, but
the implications are serious, as it casts doubt on the
efficacy of the proposed virus release. All you need
is for a certain percentage of the carp population to
survive and be resistant to the virus for the seeds of a
potentially disastrous scenario to be sown.
It is also known that infected carp will seek warm
water and that temperatures above 30 degrees Cel-
sius will block infection. So if infected but resistant
or immune or genetically polymorphic carp seek out
warm water and reproduce, the consequences could
be very significant for the proposed program.
In addition, we don’t know yet if koi herpes virus
is absent from all Australian waters. If it isn’t, and it’s
already present, it could reflect a situation found in
Japan in 2004, where a high prevalence of infection
existed, but without clear ill effects.
In view of the above, it is not in the least surpris-
ing to find that Belgian, English and Australian sci-
entists have recently called on the Australian govern-
ment to reconsider its approach to the carp problem.
According to a letter written by several scientists that
was published in Science magazine in February, the
virus release program would be ineffective and could
pose a threat to ecosystems.
The scientists suggest that, instead, the author-
ities introduce a limited testing program to assess
accurately if the virus can, indeed, control the carp
without damaging ecosystems. They maintain that
this would be a sensible approach, because, once the
full—and costly—release takes place, it would be
irreversible. They also advocate an alternative ap-
proach, supported by stakeholders, consisting of the
release of daughterless koi as a means of long-term
control of the carp.
Meanwhile, the Australian koi sector is monitoring the situation, not just with great interest, but also
with great apprehension.
John Dawes is an international ornamental aquatic industry consultant. He has written and/or edited more
than 50 books and has contributed more than 4,000 articles to hobby, trade and academic publications. He is
the editor of the OFI Journal and a consultant to Aqua-Realm, the new trade show that took place June 2017
131 Pet Product News International
Scientists Urge Australia
to Rethink Its Carp
Virus Release Program
Because koi and carp belong to the same species,
they are both lumped together when it comes to
the Australian virus release program.