|Click for full size image:.
Photo 1:T. tubifex
worms under magnification
Photo 2: The
spore in its Triactinomyxon (or TAM) stage,
about to attach itself to the scale of a
Photo 3: Young
rainbow trout exhibiting "black tail" symptoms
from WD infection.
Photo 4: This
young trout suffered bad deformities of
its jaw as a result of whirling disease
infection. It would not survive in the wild.
Photo 5: Microscopic
pictures of 1. normal cartilage in a rainbow
trout and 2. the same area of cartilage
in a rainbow trout that is infected with
the wd parasite. The vertical dark pink
is bone that is collapsing because the supporting
cartilage is gone (the parasite destroyed
by Beth MacConnell
Whirling Disease is thankfully something that
Australian Anglers have not had to give much thought to.
However with the recent talks of importing salmon from
Canada we decided to contact the Head of Montana Fish,
Wildlife and Park's Fisheries Division, Larry Peterman
and ask him a few pertinent questions on the subject.
GVFFC: Whirling Disease
has been around for a long time now. How is the fight
in North America going?
whirling disease continues to spread in the western
United States, we are learning a great deal about the
biology of the disease, how it impacts wild populations
and which species are most susceptible. We know a fair
amount about how it can be transmitted. This is helping
us develop new strategies for dealing with the disease
in our state.
GVFFC: Australian fly
fishers are particularly interested in the effect on
the waterways of Montana. How are rivers such as the
Missouri and Madison coping with WD?
the Madison and Missouri remain excellent fisheries,
they have both felt the impact of whirling disease.
The Madison initially suffered from severe declines
in the rainbow trout population. In the last 10 years,
we've seen several good year classes resulting from
high flow conditions. We are hopeful that we can time
the Spring releases from Hebgen Reservoir to more consistently
produce good year-classes in the Madison. On the Missouri,
one of three major spawning tributaries is heavily infected
with whirling disease, and this is having an impact
on rainbow trout reproduction in the first 10 miles
of the blue-ribbon stretch of the river below Holter
Dam. Brown trout are doing somewhat better, and may
eventually increase their presence in the river.
GVFFC: While it looks
like the disease is here to stay what do you believe
are the most likely ways in which it will be controlled?
Larry: As our understanding
of whirling disease biology improves, we are developing
new strategies to manage wild trout populations, including
emphasizing more resistant species, enhancing whirling
disease-free spawning areas, and managing reservoir
releases to increase flows during periods of high infection.
But we have a long way to go, and there is no silver
bullet. The solution is probably going to be more site-specific
than some overall approach for all our waters. Also,
it is essential that all of our hatcheries (private,
state, and federal) remain free of whirling disease
to prevent accidental spread.
GVFFC: We read with
some alarm on your site that Whirling Disease has been
detected in New Zealand. Could you please elaborate
on this finding?
to "New Zealand's Experience with Whirling Disease,
presented by Nelson Boustead of New Zealand's National
Institute of Water and Atmospheric Research (presented
at the 1996 Whirling Disease Workshop in Fort Collins,
Colorado), whirling disease caused by M. cerebralis
was first identified in hatchery rainbow trout in NZ
in 1971. In a 1980-1988 survey, whirling disease was
found in three rivers on the east coast of the South
Island and has since been found in chinook and sockeye
salmon and brown trout from other locations within this
area. A 1995 re-examination of wild brown trout and
rainbow trout populations in these locations revealed
a low intensity of infection in both species, and mortalities
and deformities were not associated with these infections.
Fortunately, it appears that "the effects of the disease
on local fisheries appears to be limited."
GVFFC: Australia currently
has a disease free status and the state of Tasmania
is recognized globally as one of the best trout fisheries
on the planet. While this is currently the case our
trout fisheries are under threat due to possible importation
of salmon from overseas. What would you say to the fisherman
of Australia in regards to the allowing of salmon imports
from infected countries?
Larry: We suggest
that you do everything to discourage the importation
of salmon from whirling disease-infected sources. There
are not only serious concerns about whirling disease,
but also there are a number of salmon viruses that are
present in cultured salmon stocks that can be devastating
to wild trout and salmon populations.
GVFFC: We would
like to thank Larry and his team at Montana Whirling
Disease Task Force for answering these question for
our site users. I'm sure we can speak for all Australian
fly fishers when we wish you the best of luck with your
research and hope that identified management techniques
We would ask that all of
you read on for a couple of points worth noting and
that you visit their site regularly to see just what
the state of play is in regard to this disease.
1. What is whirling
"Whirling disease" is a
disease of Salmonid fish (trout, salmon, whitefish)
caused by a microscopic parasite known as Myxobolus
cerebralis. This tiny parasite has a fairly complicated
life cycle which involves two hosts; a small worm that
lives on the bottom of a stream or other body of water,
and a fish. The fish becomes infected after a form of
the parasite (the TAM stage) emerges from the worm and
enters the water column. The parasite finds a fish,
attaches to the fish and penetrates the skin. The parasite
eventually finds its way to the cartilage of the fish
where it matures into the mature whirling disease spore.
It stays there until the fish dies, releasing spores
into the water, which ultimately are ingested by the
worms and the life cycle starts all over. In the fish
the parasite can affect nerves and cause cartilage damage
which results in the symptoms of whirling disease. Whirling
disease gets its name from the abnormal whirling or
tail-chasing behavior exhibited by some infected fish.
This is caused by damage or pressure to nerves caused
by the whirling disease parasite. Other symptoms may
include a black tail in younger fish. In older fish
symptoms sometime include deformities to the head or
2. How is it spread?
Because the parasite that
causes whirling disease has two distinct forms including
a free-floating stage in the water, and involves two
hosts, it can potentially be spread in several ways.
However, the most likely way the parasite can be spread
is through movement of live fish or parts of fish. A
single fish can be infected with many thousands of spores
(up to a million or more)! This makes infected fish
the most dangerous source of infection. In other states
movements of live infected fish have been documented
as the source of introduction of whirling disease. Because
most Montana trout streams, such as the Madison River,
rely on natural reproduction and fish are not stocked
into these waters, it is difficult to determine the
source of infection in most cases. Birds are suspected
as a potential vector of whirling disease. University
studies have shown that viable parasites can pass through
the digestive tract of birds and mammals and still be
infective to fish. Other potential sources are water
or mud on boats, trailers, fishing equipment, etc. The
mature whirling disease spore, once released from the
fish, is very hardy. It can remain live in mud for many
years and is a potential source of whirling disease
if moved from one body of water to another. Although
vectors such as birds, mud and water are potential sources
of whirling disease, live infected fish and/or heads
or other infected parts of infected fish remain the
most dangerous and most likely source of whirling disease
Visit the Montana Whirling
Disease Task Force @ http://www.whirlingdisease.org
and take a look around. This is a well designed
site with plenty of information that is regularly updated.
We would urge everyone to become familiar with WD as
with the push from Canada to force Australia to allow
importation of their salmon there exists a real threat
to our disease free salmonid fisheries.
Those of you wishing to
contact the Task Force can please see the following
Larry Peterman, Montana
Whirling Disease Task Force, 406-444-2449 firstname.lastname@example.org