University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 2001 Morphologic and genetic characterization of potential oligochaete alternate hosts of Myxobolus cerebralis Kathryn M. Sweeney The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Sweeney, Kathryn M., "Morphologic and genetic characterization of potential oligochaete alternate hosts of Myxobolus cerebralis" (2001). Graduate Student Theses, Dissertations, & Professional Papers. 9398. https://scholarworks.umt.edu/etd/9398 This Dissertation is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. 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Sweeney B.A. The University of Montana, Missoula, Montana 1996 Presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy The University of Montana 2001 Qjjtfcwtd). 1 Uiairsjan, Board of Examines Dean, Graduate School (o - 7 - 0 t Date Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 3012240 __ ® UMI UMI Microform 3012240 Copyright 2001 by Bell & Howell Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. Bell & Howell Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Sweeney, Kathryn M., Ph.D., May 2001 Biochemistry/Microbiology Morphologic and genetic characterization of potential oligochaete hosts ofMyxobolus cersbralis Director: Willard 0. Granath, Jr. huO tff . ABSTRACT Salmonid whirling disease, caused by the parasite Myxobolus cerebralis, was considered to be of concern only to fish aquaculture until the early 1990's when dramatic declines in wild trout populations in the intermountain west were attributed to the presence of the parasite. The current consensus is that oneeM cerebralis becomes established in a waterway it is probably impossible to eradicate the parasite and that management of the disease will focus on reducing the impact on salmonid fish populations. Effective management strategies will rely in part on understanding and assessing the interaction of the numerous variables of the disease, including the hosts, parasite and environment. Myxobolus cerebralis requires two hosts to complete its life cycle, salmonid fish and an oligochaete worm, Tvbifex iubifex. Extensive research has been conducted on interactions between the parasite and salmonid fish, however, less is known about the role of the oligochaete host. In this study homogeneous monocultures of tubificids were developed by utilizing the ability of Tubificidae to reproduce by parthenogenesis. These monocultures were developed from geographic variants ofT. iubifex that vary in their ability to release triactinomyxons, the form of the parasite infective to fish. Evidence is presented showing that current oligochaete identification keys based on chaetae morphology and internal male genitalia do not differentiate between T. iubifex strains that are susceptible to M. cerebralis infection with subsequent release of triactinomyxons and a resistant strain of T. iubifex that ingests the myxospore form ofM. cerebralis but the parasite does not undergo development into viable triactinomyxons. This evidence is further supported by documentation of spurred chaetae, a previously unreported chaetal form, exhibited by a T. iubifex population in Rock Creek, Montana. Further, other studies indicate this spurred chaetal form is probably environmentally induced. Generation time may be an indication that susceptible and resistant I iubifex are different species. In addition, genetic fingerprints were generated that distinguished between strains of T. iubifex that vary in susceptibility to M. cerebralis infection. Results of interbreeding experiments between M. cereirafo-susceptible and resistant T. iubifex are presented, and the potential use of resistant T. iubifex as a biological control of whirling disease is discussed. ii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS My grateful thanks to: Bill Granath for the opportunity to be involved in whirling disease research; my committee members - Mike Minnick for his ability to smile while stressed, Scott Samuels for his understanding that sometimes my eyes “leak” just when it is most inappropriate, Tom Schwan for his willingness to step into unknown territory and serve on a graduate committee and George Card without whose wisdom I may have become hopelessly lost in the labyrinth of graduate school; Robb Leary, Kathy Knudsen, Scott Manning, Deb Nycz, the late Joan Strange and Charlotte Rasmussen for technical advise and assistance; Don Christian and all of the instructors for the education I received; Janean Clark, Roni Patrick, Nancy Bernius, Gay Allison and Sherrie Wright who quietly and efficiently keep us all in line; The National Partnership on Management of Wild and Native Coldwater Fisheries for funding this study. I dedicate this work to my three sons, Craig, Cole and Chris, who had faith in my ability to cook dinner while reading a biochemistry book rather than a cookbook without giving them food poisoning, to my mother, Margaret Morgan, for her unconditional love and support and to the memory of my father, Wayne Morgan. iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS Chapter Page 1 General Introduction 1 1.1 Historical Perspective 1 1.2 Dissemination 3 1.3 Geographic Distribution 6 1.4 Diagnosis and Pathology 10 1.5 Impact 13 1.6 Prevention and Control 14 1.7 The Parasite: Myxobolus cerebralis 16 1.8 Salmonid H ost 22 1.9 Oligochaete Host: Tubificidae 23 1.10 Tubifex iubifex 31 1.20 Research Significance and Goals 35 2 Materials and Methods 37 2.1 Tubificid Monocultures 37 2.2 Morphologic Characterization 40 2.3 Genetic Characterization 41 2.4 Crossbreeding: Susceptible x Resistant T. tubifex 43 2.4 Toxicant Experiments 44 3 Results 46 3.1 Tubificid Monocultures 46 3.2 Morphologic Characterization 52 3.3 Genetic Characterization 71 3.4 Crossbreeding: Susceptible x Resistant T. tubifex 76 3.5 Toxicant Experiments 82 4 Discussion 89 4.1 Tubificid Monocultures 90 4.2 Morphologic Characterization 93 4.3 Genetic Characterization 95 4.4 Crossbreeding: Susceptible x Resistant T. tubifex 97 4.5 Conclusion 100 References 103 iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES