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Fish Disease

Author: Craig Springer

A couple of fish diseases have been in the news a lot, Whirling Disease and largemouth bass virus. There's good reason for the high profile of these two aliments. They both have the potential to damage sport fish over much of North America.

Whirling Disease infected trout
I got sick on a short vacation in Ohio last month. A nasty bug stayed with me longer than normal so I went to see my doctor. Turned out to be something only minor. He had the same thing a couple of weeks earlier. But my doctor mentioned a curious thing when I remarked that there was "something going around." I know you've heard that phrase spoken when a few folks around you get sick. As my doctor put it, there's always something going around. It struck a chord; fact is disease is ever present in populations of people, plants, and in game and fish, virtually all living organisms. According to a lung doctor I've shared a duck blind with, immune deficiency disease has always been around, but not until it reached epidemic proportions with AIDS did in get a lot of attention.

Fish die all the time as a course of nature from old age and senility, accidents, and disease. It's only when there's unusual threats to fish or large-scale die-offs that we tend to take notice. A couple of fish diseases have been in the news a lot, Whirling Disease and largemouth bass virus. There's good reason for the high profile of these two aliments. They both have the potential to damage sport fish over much of North America.

Whirling Disease Microbes
Whirling Disease can be the bane of the trout fisherman. This disease is specific to trout. It doesn't go after all fish of all ages. There is never a case; for example, where all fish are exposed in a stream, then they all get sick and die. That's not how this insidious disease works.

According to the Whirling Disease Foundation, it afflicts mostly very young trout before their bones have hardened from cartilage. A parasite called Myxobolus cerebralis embeds itself into the skull near the spine and reproduces rapidly. As the infested area grows, the parasites put pressure on the organ that helps a trout keep it balance. When the parasite grows large enough it causes the fish to swim erratically, or whirl.

The parasite spreads most commonly by live infected fish. Hatchery fish are one source. Fishermen are another. The parasite that causes Whirling Disease can attach to your waders or other gear. You walk to the next stream with the parasite attached and the disease spreads.

Ironically, Whirling Disease is not necessarily fatal. Young trout can sometimes continue to grow; their cartilage grows into bone. But infected fish are often maimed and disfigured. And as a result, they may fail to reproduce. Many young trout die not from Whirling Disease, but from secondary illness or effects. Disfigured trout can not feed as efficiently and may perish from malnutrition. Also, they are more likely eaten by predators.

Once Whirling Disease infects a trout water, because of its life cycle, it is probably there to stay. It starts as a spore, eaten by a small worm found in slack waters in streams and most anywhere in shallow portions of lakes. It's called a tubifex worm. The worm digests the spore and releases the parasite in the form that infects fish. When infected fish die, the parasites are released and able to infect other fish. The spores, that go uneaten can live up to 30 years in the water. The tubifex worm is a natural part of our aquatic ecosystems - Whirling Disease is not.

Deformed Adult Trout
Whirling Disease was introduced into the U.S. from Europe in the 1950s, and therein lies the crux of the problem. Our trout native to North America have no natural resistance to this foreign invader. Brown trout, originally native to Europe, has some natural resistance to Whirling Disease. Rainbow trout seem the most vulnerable here in North America. Other trout are also affected by the disease, but to a lesser degree. Bull trout, lake trout and grayling seem nearly immune.

Whirling Disease could put a damper on fishing in your neighborhood. It occurs in 22 states -- all of the western states and in the Northeast. It could also set back important conservation efforts, too. Whirling Disease could be the Achilles heel to ongoing conservation efforts for rare trout species in the West. Greenback cutthroat trout in Colorado, golden trout in the Sierra Nevadans, Apache trout in Arizona - these fish at one time stared extinction squarely in its ugly face. But not so today. Thanks to diligent fish biologists, they all provide unique sport fishing opportunities. Whirling Disease, should it be spread, could change that.

Largemouth Bass Virus
Bass fishermen have their own disease to worry about, Largemouth Bass Virus. This malady recently showed up, first discovered in South Carolina's Santee Cooper Reservoir in 1995, when about 1,000 largemouth bass died. It seems to target the swim bladder, causing fish to lose the ability to stay upright. Infected bass may look bloated. Largemouth Bass Virus has been found in other species of bass and sunfishes, even in trout, but has been only fatal to largemouths. Largemouth Bass Virus infects only cold-blooded animals so humans can not catch the disease.

Scientists are not entirely sure if this is a new disease, but some say that it has probably been around for some time, given that it has been found in Alabama, Arkansas, Florida, Georgia, Indiana, Kentucky, Louisiana, Michigan, Missouri, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, and Texas.

Unlike Whirling Disease, Largemouth Bass Virus does not appear to be so devastating. Granted, Largemouth Bass Virus seems to attack mostly larger fish, and no one can take solace in big fish dying, but fact is, Largemouth Bass Virus die-offs are limited and sporadic. No large-scale fish kills have occurred from this virus, and populations affected by the virus seem to rebound in short order. More bass are killed from pollution than this virus.

Largemouth Bass Virus has shown up in fish that exhibit no sign of sickness. That's like you carrying a cold germ, but not getting sick. You could spread that cold germ and make others sick. You could also spread Largemouth Bass Virus. Auburn University scientist, John Grizzle learned that Largemouth Bass Virus lives outside a fish's body for maybe as long as four hours. Think about that and what it means for your live well. You could unknowingly spread Largemouth Bass Virus to other reservoirs through your bilge and live well.

As with your own personal health, prevention is the first line of defense. And so it is with our trout and bass fisheries. Here's some things you can do to prevent the spread of disease. First, never move live fish from one water to another. Never. Always clean your waders and other gear of mud. Keep a clean live well and always drain the bilge before going to another lake. An ounce of prevention is worth a pound of cure.





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