While fishing the Gallatin River over the past week, I brought two fish to hand in two different stretches of the river, which displayed some very unusual physical characteristics. Rather than the usual bullet-shaped head and nose of a typical Montana Rainbow, these two trout had severely deformed, for lack of a better description, "forehead" regions. It was as if the normal tapering of a Rainbow's body stopped just above the eye, and took a 60 degree turn down, almost concave in shape. After the second siting, I decided it was enough cause to call the Montana Fish and Wildlife Department in search of an explanation. After relaying this information to an aquatic specialist, he indicated that the phenomena, which I witnessed were a result and case of Whirling Disease. Whirling Disease, caused by "Myxobolus cerebralis is a metazoan parasite that penetrates the head and spinal cartilage of fingerling trout where it multiplies very rapidly, putting pressure on the organ of equilibrium. This causes the fish to swim erratically (whirl), and have difficulty feeding and avoiding predators. In severe infections, the disease can cause high rates of mortality in young-of-the-year fish. Those that survive until the cartilage hardens to bone can live a normal life span, but are marred by skeletal deformities. Fish can, however reproduce without passing on the parasite to their offspring. The minute organism, native to the Eurasian continent, was introduced into North American waters in the late 1950s. So far its severe damage has been primarily to wild rainbow populations, although many other salmonid species can become infected, with or without clinical disease. Brown trout, also a European import, become infected by M.cerebralis, but rarely suffer clinical disease. Under some circumstances infected browns suffer some mortality, but they always insure the survival of the parasite. Regardless of species, when each infected fish dies, many thousands to millions of the parasite spores are released to the water.Therein lies the gravity of the whirling disease problem. M. cerebralis is virtually indestructible -- the spore can withstand freezing and desiccation, and can survive in a stream for 20 to 30 years. Eventually, it must be ingested by its alternate host, a tiny and common aquatic worm known as Tubifex tubifex, where the spore takes on the form that once again will infect trout fry. The parasite is sure to continue to spread to drainages now clean, since it is so easily and unknowingly transported by animals, birds and humans." (courtesy of The Whirling Disease Foundation, Bozeman, MT (www.whirling-disease.org).
Fish exposed to Whirling Disease will most normatively display the following characteristics: darkened tail, twisted spine, shortened or twisted jaw, and or deformed head.
As the specialist at Montana Fish & Wildlife described, Whirling disease, after it's widespread outbreak in Montana during the 1990's, but having been there long before that, will remain in America's rivers for the foreseeable future, as it is nearly impossible to eradicate the pathogen altogether, but merely control it's influence and spread. I was told by owner of Gallatin Riverguides, Betsey French, that during the 1990's outbreak anglers fishing affected waters were pleaded with to soak their felt soled boots in bleach after wading in an attempt to control further infestation not only in concern for other rivers in the area, but also the next patch of water an angler might step foot in. Since the microbe causing Whirling Disease can survive for prolonged periods of time throughout the gamut of climactic conditions, the pathogen can be traverse great distances spanning great lengths of time. This resiliency makes the disease extremely dangerous and difficult to fully control, only exacerbating the possibility of a full-blown outbreak. The Montana Fish & Wildlife Department regularly monitors the percentage of trout affected through shocking procedures tested on all of Montana's waterways. From what I gathered, the disease has been working it's way out of Montana's river systems since the 1990's fiasco. Here is a list of precautions you can take to prevent the spread of this highly infectious and toxic disease, also courtesy of the Whirling Disease Foundation.
Anglers, boaters, and others can make a difference in reducing the chances of spreading
whirling disease. Distribution of the parasite is expanding rapidly in some areas, so you
should assume its presence if you don't know otherwise. Recommended precautions that
will help prevent not only the spread of whirling disease, but also other disease-causing
organisms and aquatic pests include:
1. Never transport live fish from one water body to another. (This is illegal in many
states.)
2. Do not use trout, whitefish, or salmon parts as cut bait.
3. Dispose of fish entrails and skeletal parts properly. Never discard fish parts in or near
streams or rivers. Because an infected fish may harbor tens of thousands of
myxospores, simply disposing of infected fish parts in a clean drainage could provide
enough spores to start an infection. Do not discard fish parts in a kitchen disposal.
Whirling disease myxospores can survive most wastewater treatment systems. Instead,
discard in dry waste that would go to a landfill.
4. Rinse all mud and debris from equipment and wading gear, and drain water from
boats before leaving an infected drainage. This is good practice for preventing transfer
of other aquatic hitchhikers as well.
5. Although the above precautions will remove most spores from your gear, you may want
to consider the following if fishing in heavily infected waters:
! Rinse, then thoroughly dry your boots, waders and other fishing equipment. This is
generally sufficient to kill the TAM stage of the parasite.
! Chlorine (regular household bleach) is a very effective disinfectant, and one of the
few that can kill all stages of the parasite if used at the proper concentration.
However, chlorine is a very strong chemical and can harm your equipment with
prolonged exposure, so make sure you rinse the chlorine off your waders and other
equipment after you disinfect, and dry in the shade.
• To kill the TAM stage, use 1 part chlorine to 32 parts water. It must stay in
contact for about 10 minutes to assure disinfection.
• To kill the mature myxospore that may be found in the mud from an infected
stream is much more difficult and hard on equipment.
o 50% solution (1 part chlorine to 1 part water) - dip waders into a
solution of the bleach or wipe or spray it on.
o 10% solution (1 part chlorine to 9 parts water) and soak your
equipment for 10 minutes.
! Quaternary ammonium compounds are also effective in killing both parasite stages.
These disinfectants are commercially available for disinfecting fishing equipment
(Bright Water TM) or for the pet/veterinary trade (Roccal-D TM, Parvosol TM).
! Equally effective is water heated to nearly boiling (200°F) poured over your gear
and allowed to cool.
Thanks for listening, and if you or someone you know experiences what they think may be a fish affected by Whirling Disease, please contact your local Fish and Wildlife Department. Cheers. (visual courtesy of www.wikipedia.com)
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