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 trout. l   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 it). All Photos by Beth MacConnell

GVFFC: Whirling Disease has been around for a long time now. How is the fight in North America going?

Larry: Although 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?

Larry: Although 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?

Larry: According 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 are successful.

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 disease?

"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 body.

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 infection.

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 contact details:

Larry Peterman, Montana Whirling Disease Task Force, 406-444-2449 taskforce@whirlingdisease.com

http://www.whirlingdisease.org

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