When you hear the word “trout”, perhaps you think of an angler displaying a specimen of these beautiful sportfish before releasing it back into the water. Maybe you picture an osprey swooping down to seize a trout in its talons. Or you might picture one of the top predators of a small stream lurking in the deeper pools and emerging to keep populations of everything from sculpins to caddisflies in check.
Photo by Jamie MacArthur.
One thing nobody wants to picture is a fish on the brink of death, its blackened tail and warped skeleton forcing it to spend its last days swimming in rabid circles. Unfortunately, the spread of whirling disease in North America is making this sad image a reality for numerous populations of trout and other cold water sportfish.
Whirling disease is somewhat deceptively named. Although we frequently think of a disease as the effect of a virus or bacterial strain on the body, this is not true of whirling disease. Whirling disease begins not with bacterial or viral reproduction, but with the introduction of a non-native protozoan. Myxobolus Cerebralis begins its life cycle as a spore, too tiny to attract the notice of all but the smallest of predators. These predators, known as tubifex worms, live in the mud of river bottoms. When they feed on the Myxobolus spores, they unwittingly initiate a deadly cycle whose effects are felt far up the food chain.
The innards of a tubifex worm provide a safe haven for the Myxobolus spores to develop into a free-swimming triactinomyxon (a “TAM” for those of us who have trouble with tongue-twisters). These parasites can enter a fish in one of two ways: they can be ingested with an infected tubifex worm, or they can attach to the fish and burrow in through its flesh. Once a fish is infected, the TAM causes severe pain and spinal deformities as it feasts and breeds within its cartilage.
Infected trout; photo via Oregon State University.
As the infection worsens, the infected fish loses much of its ability to feed and evade predators. It spends its final days swimming in circles, releasing Myxobolus spores from its gills and feces. This not only perpetuates the cycle in one stream, but allows it to spread throughout a watershed. The Myxobolus spores are too small to see, and can survive for over 20 years in river sediment.
Whirling disease affects mainly salmonids, with rainbow trout being the most prominently susceptible. Because this parasite feeds and breeds in cartilage, younger fish are more susceptible than older fish.
The best way to stop the spread of whirling disease is to stop the spread of infected sediment. Boat bottoms, boot bottoms, or even a fishing reel that took a plunge into infected mud must be carefully cleaned and sanitized immediately after leaving whirling disease-infected waters. To ensure that this practice becomes commonplace among anglers, boaters, and other users of our waterways, many fisheries departments employ equipment inspectors to make sure everybody is following proper prevention procedures.
You can contribute to the fight against whirling disease by raising awareness of the way it threatens your area. Equipment inspectors, research biologists, conservation groups, and local governments must all work together to eliminate this invasive parasite from our native waters. By using crowdfunding to contribute to their efforts, you can help them be more effective at protecting your watershed from whirling disease. Fishing clubs are a particularly good audience to reach out to for these crowdfunding efforts, because they generally already have a passionate interest in protecting the fisheries they love.
Painting by Logan Davis.
Knowing how to protect the environment frequently requires fighting not only manmade problems, but also problems that show up in the form of invasive plants and animals. Whirling disease is a particularly nasty example of an invasive threat to fisheries across the nation. Fortunately, you can combat this threat by following equipment-cleaning procedures, raising awareness, and helping to fund the efforts to fight the spread of whirling disease in your watershed.
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Posted by Mark Contorno.