Detailed Research Information

Detailed project information for
Study Plan Number 01109

Branch : Fish Health Branch

Study Plan Number : 01109

Study Title : Genetics of Resistant Strains of Salmonids to Myxbolus cerebralis

Starting Date : 07/01/2004

Completion Date : 06/30/2006

Principal Investigator(s) : Beauchamp, Katherine A.; Blazer, Vicki S.

Primary PI : Beauchamp, Katherine A.

Telephone Number : (304) 724-4455

Email Address : kbeauchamp@usgs.gov

SIS Number :

Primary Program Element :

Second Program Element :

Status : Completed

Abstract : BACKGROUND

The dramatic decline in survival among several wild rainbow trout Oncorhynchus mykiss populations in the western United States has been attributed to Whirling Disease. At the 7th Whirling Disease Symposium, in 2001, consensus was reached that one of the main avenues of inquiry which deserved priority was the search for strains salmonids in particular, rainbow trout that has increased resistance to Myxobolus cerebralis, the causative agent of Whirling Disease. Recent laboratory studies have shown that the Hofer strain of rainbow trout reared in Bavaria Germany have a high resistance to whirling disease when compared with the North American Trout Lodge strain from Washington (El-Matbouli et. al. 2002, Hedrik et al. 2002). Resistant rainbow have also been identified in high elevation lakes in Montana (DeSmet) (R. Vincent, unpublished data). However, in the case of the Hofer strain of rainbow, resistance is defined as simply a lower infection rate, often accompanied by a lack of clinical signs. A number of experimental exposures (up to 2,000 tams per fish at 5-7 wks of age) in our laboratory, using lake trout have indicated some populations, under normal conditions, are totally refractory or resistant to whirling disease. Controlled laboratory exposures of rainbow trout, Atlantic salmon and lake trout indicated rainbow were highly susceptible, as expected, Atlantic salmon were intermediate (showed no clinical signs, lower number of infected individuals and lower spore counts for those infected) and lake trout refractory - no histological evidence of infection or spores (Blazer et al. 2004).

Conversely, Wagner et al. (2002) exposed lake trout to 1,000 tams per fish at 10 weeks of age and sampled at either 5 or 20 weeks. Interestingly, by PCR 100% of the 20 lake trout sampled were either positive or weakly positive at 5 weeks, as were 100% of brook trout. However, at 10 weeks by spore enumeration only 13.6% of 22 lake trout were positive, while 100% of the brook trout remained positive. Blacktail and whirling behavior were not observed for any of the lake trout, however, 9.5% did show cranial deformities. This correlates well with follow-up studies conducted at Leetown using labeled tams. Preliminary results suggest that the tams are able to attach and enter the epithelium of the lake trout but do not progress to infections of cartilage and development of mature myxospores.

Historically, classification of trout diversity has proven problematic. At present, most biologists recognize one rainbow trout species (Oncorhynchus mykiss) with 10 genetically distinct forms found throughout North America (Benke 1992). However, most farmed trout shipments originated from one small region, the lower McCloud River in California and are not representative of trout diversity (Dollar and Katz 1964). Loss of native habitat and human-mediated transfers among previously distinct populations has eroded natural variability and genetic diversity. Mitochondria DNA (mtDNA) analysis has proven a powerful tool for assessing intraspecific population genetic structure and phylogeographic patterns in many fish species (Kocher and Stepien 1997). Recent studies on the systematic importance of the mtDNA control region (displacement loop or D-loop) as a major source of sequence variation between closely related salmonid species and as an area that holds great practical value for the potential development of strain-specific probes for population studies and stock identification (Bagley and Gall 1998, Nielsen et al. 1997).

OBJECTIVES

In this study, we will utilize DNA sequence variability in the mitochondrial genome to assess the genetic variability and relatedness among resistant Hofer and DeSmet strains and susceptible Trout Lodge strain of rainbow trout. Additional sequence analysis with previously published sequences of rainbow trout in California and Nevada will be used to assess relatedness of the resistant strain to 10 native groups in the rainbow trout series. The genetic relationships of the populations studied will be evaluated and the potential relevance of observed differences between the rainbow trout strains will be used to determine the origin of resistant strains to M. cerebralis infections from hatchery (Hofer) and wild (DeSmet) populations and for the development of DNA probes to identify other resistant rainbow trout. In addition, we will compare three groups of lake trout using the DNA probes developed for rainbow trout. Two captive brood stock populations are present in the Northern Appalachian Research Laboratory, Wellsboro, PA. Group one is a population of lake trout maintained in the laboratory from more than 10 years. There has been no attempt to maintain genetic diversity of this population. Group two fish were brought to the Wellsboro laboratory in 2003 as 5 year old fish. The fish are from a group with a breeding plan to maintain genetic diversity. Wild fish are routinely introduced into the population for the purpose of keeping the genetic diversity similar to feral Great Lakes populations. Group three fish are from a population of lake trout successfully infected in exposure studies at the Egan Hatchery from Logan, UT.

A better understanding of resistance mechanisms for M. cerebralis and a basis for further studies on how various genetic phenomenon (inbreeding, hybridization, gene flow) and abiotic disturbances (contaminants, nutritional factors, habitat changes) may affect these mechanisms. Information can be used for the development of strain specific markers to identify resistant strains and to investigate appropriate management strategies for the use of these resistant strains to prevent or contain infection in a given watershed.

HYPOTHESIS TO BE TESTED

1. Different species/strains of salmonids show differences genetic diversity in susceptibility to infection to M. cerebralis.

2. Individuals that fail to develop clinical disease infection or disease have lower degree of inbreeding than susceptible fish.

3. Resistant species of salmonids may be show higher levels of genetic diversity than susceptible species.

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Branch :	Fish Health Branch
Study Plan Number :	01109
Study Title :	Genetics of Resistant Strains of Salmonids to Myxbolus cerebralis
Starting Date :	07/01/2004
Completion Date :	06/30/2006
Principal Investigator(s) :	Beauchamp, Katherine A.; Blazer, Vicki S.
Primary PI :	Beauchamp, Katherine A.
Telephone Number :	(304) 724-4455
Email Address :	kbeauchamp@usgs.gov
SIS Number :
Primary Program Element :
Second Program Element :
Status :	Completed
Abstract :	BACKGROUND The dramatic decline in survival among several wild rainbow trout Oncorhynchus mykiss populations in the western United States has been attributed to Whirling Disease. At the 7th Whirling Disease Symposium, in 2001, consensus was reached that one of the main avenues of inquiry which deserved priority was the search for strains salmonids in particular, rainbow trout that has increased resistance to Myxobolus cerebralis, the causative agent of Whirling Disease. Recent laboratory studies have shown that the Hofer strain of rainbow trout reared in Bavaria Germany have a high resistance to whirling disease when compared with the North American Trout Lodge strain from Washington (El-Matbouli et. al. 2002, Hedrik et al. 2002). Resistant rainbow have also been identified in high elevation lakes in Montana (DeSmet) (R. Vincent, unpublished data). However, in the case of the Hofer strain of rainbow, resistance is defined as simply a lower infection rate, often accompanied by a lack of clinical signs. A number of experimental exposures (up to 2,000 tams per fish at 5-7 wks of age) in our laboratory, using lake trout have indicated some populations, under normal conditions, are totally refractory or resistant to whirling disease. Controlled laboratory exposures of rainbow trout, Atlantic salmon and lake trout indicated rainbow were highly susceptible, as expected, Atlantic salmon were intermediate (showed no clinical signs, lower number of infected individuals and lower spore counts for those infected) and lake trout refractory - no histological evidence of infection or spores (Blazer et al. 2004). Conversely, Wagner et al. (2002) exposed lake trout to 1,000 tams per fish at 10 weeks of age and sampled at either 5 or 20 weeks. Interestingly, by PCR 100% of the 20 lake trout sampled were either positive or weakly positive at 5 weeks, as were 100% of brook trout. However, at 10 weeks by spore enumeration only 13.6% of 22 lake trout were positive, while 100% of the brook trout remained positive. Blacktail and whirling behavior were not observed for any of the lake trout, however, 9.5% did show cranial deformities. This correlates well with follow-up studies conducted at Leetown using labeled tams. Preliminary results suggest that the tams are able to attach and enter the epithelium of the lake trout but do not progress to infections of cartilage and development of mature myxospores. Historically, classification of trout diversity has proven problematic. At present, most biologists recognize one rainbow trout species (Oncorhynchus mykiss) with 10 genetically distinct forms found throughout North America (Benke 1992). However, most farmed trout shipments originated from one small region, the lower McCloud River in California and are not representative of trout diversity (Dollar and Katz 1964). Loss of native habitat and human-mediated transfers among previously distinct populations has eroded natural variability and genetic diversity. Mitochondria DNA (mtDNA) analysis has proven a powerful tool for assessing intraspecific population genetic structure and phylogeographic patterns in many fish species (Kocher and Stepien 1997). Recent studies on the systematic importance of the mtDNA control region (displacement loop or D-loop) as a major source of sequence variation between closely related salmonid species and as an area that holds great practical value for the potential development of strain-specific probes for population studies and stock identification (Bagley and Gall 1998, Nielsen et al. 1997). OBJECTIVES In this study, we will utilize DNA sequence variability in the mitochondrial genome to assess the genetic variability and relatedness among resistant Hofer and DeSmet strains and susceptible Trout Lodge strain of rainbow trout. Additional sequence analysis with previously published sequences of rainbow trout in California and Nevada will be used to assess relatedness of the resistant strain to 10 native groups in the rainbow trout series. The genetic relationships of the populations studied will be evaluated and the potential relevance of observed differences between the rainbow trout strains will be used to determine the origin of resistant strains to M. cerebralis infections from hatchery (Hofer) and wild (DeSmet) populations and for the development of DNA probes to identify other resistant rainbow trout. In addition, we will compare three groups of lake trout using the DNA probes developed for rainbow trout. Two captive brood stock populations are present in the Northern Appalachian Research Laboratory, Wellsboro, PA. Group one is a population of lake trout maintained in the laboratory from more than 10 years. There has been no attempt to maintain genetic diversity of this population. Group two fish were brought to the Wellsboro laboratory in 2003 as 5 year old fish. The fish are from a group with a breeding plan to maintain genetic diversity. Wild fish are routinely introduced into the population for the purpose of keeping the genetic diversity similar to feral Great Lakes populations. Group three fish are from a population of lake trout successfully infected in exposure studies at the Egan Hatchery from Logan, UT. A better understanding of resistance mechanisms for M. cerebralis and a basis for further studies on how various genetic phenomenon (inbreeding, hybridization, gene flow) and abiotic disturbances (contaminants, nutritional factors, habitat changes) may affect these mechanisms. Information can be used for the development of strain specific markers to identify resistant strains and to investigate appropriate management strategies for the use of these resistant strains to prevent or contain infection in a given watershed. HYPOTHESIS TO BE TESTED 1. Different species/strains of salmonids show differences genetic diversity in susceptibility to infection to M. cerebralis. 2. Individuals that fail to develop clinical disease infection or disease have lower degree of inbreeding than susceptible fish. 3. Resistant species of salmonids may be show higher levels of genetic diversity than susceptible species.
For More Information :
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U.S. Department of the Interior \|\| U.S. Geological Survey 11700 Leetown Road, Kearneysville, WV 25430, USA URL: http://www.lsc.usgs.gov Maintainer: lsc_webmaster@usgs.gov Last Modified: October 21, 2002 dwn Privacy Policy and Disclaimers \|\| FOIA \|\| Accessibility