Detailed Research Information

Detailed project information for
Study Plan Number 01064-08

Branch : Fish Health Branch

Study Plan Number : 01064-08

Study Title : Whirling disease research

Starting Date : 03/01/1997

Completion Date : 03/31/2004

Principal Investigator(s) : Blazer, Vicki S.; Schill, Bane (William) & Densmore, Christine

Primary PI : Blazer, Vicki S.

Telephone Number : (304) 724-4434

Email Address : vicki_blazer@usgs.gov

SIS Number : 5001515

Primary Program Element : Fisheries and Aquatic Resources

Second Program Element : Fish and Aquatic Habitats

Status : Completed

Abstract : BACKGROUND
The whirling disease parasite, Myxobolus cerebras, is believed to have been introduced from Europe with shipments of frozen fish in the late 1950's. Following its introduction and spread the disease was included by the Fish and Wildlife Service (CFR Title 50), the Canadian Department of Fisheries and Ocean and many state agencies in regulations prohibiting entry of fish with the parasite. Condemnation of entire hatcheries and confiscation and destruction of infected fish were the rule for handling outbreaks. Whirling disease is caused by a parasite, classified as a member of the Myxosporea. Myxosporean parasites were known for many years as parasites of vertebrates and actinosporeans as parasites of annelid worms, but the alternating life cycle, recognized for whirling disease in the early 1980's had not been understood. This complex life cycle has since been demonstrated for numerous myxosporean parasites of fish (Kent et al. 1994). The life cycle of M. cerebralis was not elucidated until work by researchers at the Leetown Fish Health Lab in the 1980's, showed it required an intermediate tubificid worm host (Markiw and Wolf 1983; Wolf and Markiw 1984) in which a triactinomyxon spore develops (Markiw 1986). Once this life cycle was understood, it was believed the disease could be managed by culturing fish in spore-free source water, in concrete raceways or in ponds that were regularly disinfected. It was further suggested that fish which carried the spores could still be healthy and were even suitable for stocking into waters where whirling disease was already present (Hoffman 1990). Tubifex tubifex was the only species of worm definitively shown to harbor the infective stages in laboratory exposures (Markiw and Wolf 1983; Wolf et al. 1986). Infected worms were reported to be pale, have generalized anterior swelling and display an opaque outer layer (Wolf et al. 1986). It must be recognized that these worms are very difficult to speciate morphologically, especially the immature stages. Hence, an important need is to develop molecular markers to identify various species/genera of worms. Early work also indicated that there was a difference in susceptibility of salmonid species with rainbow trout the most susceptible, brook trout less susceptible and brown trout the most resistant (Hoffman et al. 1962).

In 1993-94 the complacency which had developed in the late 1980's changed when significant population declines of wild rainbow trout in several "blue ribbon" trout streams in Colorado and Montana, most notably the Madison River, were attributed to whirling disease. In the Madison River it has been reported that the trout population has declined from 3500 fish per sq. mile in 1990 to 300 fish per sq. mile in 1994 (Potera, 1997). Whirling disease was also thought to be a decisive factor in the collapse of wild rainbow trout recruitment in the upper Colorado River. This has lead to renewed concern about the potential impacts of whirling disease not only on salmonid species of sportfishing and economic interest, but also on threatened and endangered salmonid species. The disease is currently known to occur in at least 21 states and has become a highly significant problem for fisheries managers of the U.S. Fish and Wildlife Service as well as many state agencies.

Two major scientific conferences were held in early 1996 - one in Denver, CO (February) and one in Bozeman, MT (May) to discuss current issues and come to some consensus on a research agenda. In addition, the Fish and Wildlife Service requested and received increased funding in FY97 to address some of the high priority research areas. One very interesting aspect of the whirling disease puzzle is that for many years it has been recognized that there are wild populations of salmonids on the East Coast with whirling disease and yet populations have apparently not declined. If this is the case, it raises a number of questions. Are there genetic differences in parasite isolates which could account for increased/decreased resistance of fish? Are there different species/subspecies of worms that have different susceptibilities? Are there inherent differences in fish strains that account for increased/decreased resistance? Are there environmental factors that contribute to susceptibility/severity of parasite infections'? Do these factors affect the worm, the fish or both'? It was recognized that to address some of these questions is was necessary to establish reference stocks of worms, parasites and fish from different geographical areas. The Fish and Wildlife Service requested that a cooperative proposal be submitted by Ron Hedrick, University of Califorrnia - Davis, Jim Winton, Northwest Science Center, BRD/USGS and Vicki Blazer, Leetown Science Center, BRD/USGS (see attachment). This project was funded and constitutes the work to be done in this study plan.

OBJECTIVES

1. Establish reference stocks of fish, worms and parasites.

2. Identify resistant salmonids.

3. Compare parasite strains, geographic distribution and virulence

4. Studies on the alternate worm host.

5. Studies on the development of resistance.

6. Study the effects of environmental variables on development of whirling disease
HYPOTHESES TO BE TESTED
I. Parasites, worm and fish hosts from various geographic areas are similar genetically.

2. Fish strains from the East Coast respond identically to the sporozoan parasite from East Coast infections, as do those from western or mid-continent sources.

3. Salmonid species and strains differ in resistance to whirling disease and the factors responsible for this resistance can be identified.

4. Worm hosts from different geographic areas differ in their response to the parasite hosts.

5. Environmental factors such as hardness, pH, temperatures and selected contaminants have no effect on the development of whirling disease.

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Branch :	Fish Health Branch
Study Plan Number :	01064-08
Study Title :	Whirling disease research
Starting Date :	03/01/1997
Completion Date :	03/31/2004
Principal Investigator(s) :	Blazer, Vicki S.; Schill, Bane (William) & Densmore, Christine
Primary PI :	Blazer, Vicki S.
Telephone Number :	(304) 724-4434
Email Address :	vicki_blazer@usgs.gov
SIS Number :	5001515
Primary Program Element :	Fisheries and Aquatic Resources
Second Program Element :	Fish and Aquatic Habitats
Status :	Completed
Abstract :	BACKGROUND The whirling disease parasite, Myxobolus cerebras, is believed to have been introduced from Europe with shipments of frozen fish in the late 1950's. Following its introduction and spread the disease was included by the Fish and Wildlife Service (CFR Title 50), the Canadian Department of Fisheries and Ocean and many state agencies in regulations prohibiting entry of fish with the parasite. Condemnation of entire hatcheries and confiscation and destruction of infected fish were the rule for handling outbreaks. Whirling disease is caused by a parasite, classified as a member of the Myxosporea. Myxosporean parasites were known for many years as parasites of vertebrates and actinosporeans as parasites of annelid worms, but the alternating life cycle, recognized for whirling disease in the early 1980's had not been understood. This complex life cycle has since been demonstrated for numerous myxosporean parasites of fish (Kent et al. 1994). The life cycle of M. cerebralis was not elucidated until work by researchers at the Leetown Fish Health Lab in the 1980's, showed it required an intermediate tubificid worm host (Markiw and Wolf 1983; Wolf and Markiw 1984) in which a triactinomyxon spore develops (Markiw 1986). Once this life cycle was understood, it was believed the disease could be managed by culturing fish in spore-free source water, in concrete raceways or in ponds that were regularly disinfected. It was further suggested that fish which carried the spores could still be healthy and were even suitable for stocking into waters where whirling disease was already present (Hoffman 1990). Tubifex tubifex was the only species of worm definitively shown to harbor the infective stages in laboratory exposures (Markiw and Wolf 1983; Wolf et al. 1986). Infected worms were reported to be pale, have generalized anterior swelling and display an opaque outer layer (Wolf et al. 1986). It must be recognized that these worms are very difficult to speciate morphologically, especially the immature stages. Hence, an important need is to develop molecular markers to identify various species/genera of worms. Early work also indicated that there was a difference in susceptibility of salmonid species with rainbow trout the most susceptible, brook trout less susceptible and brown trout the most resistant (Hoffman et al. 1962). In 1993-94 the complacency which had developed in the late 1980's changed when significant population declines of wild rainbow trout in several "blue ribbon" trout streams in Colorado and Montana, most notably the Madison River, were attributed to whirling disease. In the Madison River it has been reported that the trout population has declined from 3500 fish per sq. mile in 1990 to 300 fish per sq. mile in 1994 (Potera, 1997). Whirling disease was also thought to be a decisive factor in the collapse of wild rainbow trout recruitment in the upper Colorado River. This has lead to renewed concern about the potential impacts of whirling disease not only on salmonid species of sportfishing and economic interest, but also on threatened and endangered salmonid species. The disease is currently known to occur in at least 21 states and has become a highly significant problem for fisheries managers of the U.S. Fish and Wildlife Service as well as many state agencies. Two major scientific conferences were held in early 1996 - one in Denver, CO (February) and one in Bozeman, MT (May) to discuss current issues and come to some consensus on a research agenda. In addition, the Fish and Wildlife Service requested and received increased funding in FY97 to address some of the high priority research areas. One very interesting aspect of the whirling disease puzzle is that for many years it has been recognized that there are wild populations of salmonids on the East Coast with whirling disease and yet populations have apparently not declined. If this is the case, it raises a number of questions. Are there genetic differences in parasite isolates which could account for increased/decreased resistance of fish? Are there different species/subspecies of worms that have different susceptibilities? Are there inherent differences in fish strains that account for increased/decreased resistance? Are there environmental factors that contribute to susceptibility/severity of parasite infections'? Do these factors affect the worm, the fish or both'? It was recognized that to address some of these questions is was necessary to establish reference stocks of worms, parasites and fish from different geographical areas. The Fish and Wildlife Service requested that a cooperative proposal be submitted by Ron Hedrick, University of Califorrnia - Davis, Jim Winton, Northwest Science Center, BRD/USGS and Vicki Blazer, Leetown Science Center, BRD/USGS (see attachment). This project was funded and constitutes the work to be done in this study plan. OBJECTIVES 1. Establish reference stocks of fish, worms and parasites. 2. Identify resistant salmonids. 3. Compare parasite strains, geographic distribution and virulence 4. Studies on the alternate worm host. 5. Studies on the development of resistance. 6. Study the effects of environmental variables on development of whirling disease HYPOTHESES TO BE TESTED I. Parasites, worm and fish hosts from various geographic areas are similar genetically. 2. Fish strains from the East Coast respond identically to the sporozoan parasite from East Coast infections, as do those from western or mid-continent sources. 3. Salmonid species and strains differ in resistance to whirling disease and the factors responsible for this resistance can be identified. 4. Worm hosts from different geographic areas differ in their response to the parasite hosts. 5. Environmental factors such as hardness, pH, temperatures and selected contaminants have no effect on the development of whirling disease.
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