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Gyrodactylid Biology, Transmission and Control

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Gyrodactylid Biology, Transmission and Control Gyrodactylid Biology, Transmission and Control Bettina Schelkle Organisms and Environment Research Group School of Biological Sciences University of Cardiff A dissertation submitted to the University of Cardiff in accordance with the requirements of the degree of Doctor of Philosophy in the Faculty of Biological Sciences School of Biosciences, Cardiff University September 2012 DECLARATION This work has not been submitted in substance for any other degree or award at this or any other university or place of learning, nor is being submitted concurrently in candidature for any degree or other award. Signed (candidate) Date: 23 February 2013 STATEMENT 1 This thesis is being submitted in partial fulfillment of the requirements for the degree of PhD Signed (candidate) Date: 23 February 2013 STATEMENT 2 This thesis is the result of my own independent work/investigation, except where otherwise stated. Other sources are acknowledged by explicit references. The views expressed are my own. Signed (candidate) Date: 23 February 2013 STATEMENT 3 I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loan, and for the title and summary to be made available to outside organisations. Signed (candidate) Date: 23 February 2013 STATEMENT 4: PREVIOUSLY APPROVED BAR ON ACCESS I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loans after expiry of a bar on access previously approved by the Academic Standards & Quality Committee. Signed (candidate) Date: 23 February 2013 II The contents of Chapters 6-8 and Appendix IV-VII in this thesis are covered by a confidentiality agreement and conform to the ethical policy of WALTHAM Centre for Pet Nutrition. Chapters 2-5 and Appendices I, II and III were independent studies funded by the Biotechnology and Biological Sciences Research Council. All work on vertebrate animals was regulated by Cardiff University ethical policies and UK Home Office Licence procedures. III ABSTRACT Infectious disease in aquaculture is omnipresent, but traditional treatments used against the causative agents often have broad anti-parasitic properties, are not 100 % efficacious, are toxic to humans, fish and the environment, and successful application is challenging. Hence, integrated disease management that combines an understanding of parasite life history and host welfare with treatment is highly recommended. This thesis examined the life history characteristics of a ubiquitous genus of fish ectoparasites, Gyrodactylus species, and tested the efficacy of botanical treatments against gyrodactylids using the guppy (Poecilia reticulata) infected by G. turnbulli or G. bullatarudis as model, with the aim to work towards an integrated management plan for gyrodactylosis in the ornamental fish industry and the hobbyist market. The experiments conducted have shown that (1) gyrodactylids engage in sexual reproduction and on a population level show hybrid fitness and/or inter-strain competition when diverged genotypes are recombined; (2) parasite transmission is mainly driven by direct contact with potential hosts and on dead fish or after detachment gyrodactylids have a window of opportunity to re-attach of over 20 h; (3) extreme habitats provide guppies with a refuge from microbial and gyrodactylid infections in natural populations; (4) anti-parasitic treatment efficacy may be species specific using traditional methods; and (5) salt, garlic, cajuput oil and a combination treatment of the two commercially available treatments Melafix® and Pimafix® are efficacious alternatives for broad anti-parasitic aquarium treatments against gyrodactylids. Due to their efficient reproduction, gyrodactylids are unlikely to be eradicated, as just a single, pregnant worm can trigger a new disease epidemic. However, combining the knowledge on pathogen life history characteristics and host-parasite interactions with effective treatment application will reduce evolutionary pressures on the pathogen and slow its virulence evolution. Overall, this increases the time available for treatment efficacies to be maintained in a manner which corresponds with new drugs being developed as treatment resistance arises. IV ACKNOWLEDGEMENTS Firstly, I would like to thank my supervisor Dr. Jo Cable for her continuous support, encouragement, and extremely valuable advice throughout the whole of my PhD. Thank you also to Dr. Cock van Oosterhout (University of West Anglia) and Prof. David Lloyd (Cardiff University) for discussion and feedback on guppy parasite ecology and statistics and plant extract chemistry, respectively. My PhD was funded through a CASE studentship by the Biotechnology and Biological Sciences Research Council in collaboration with the WALTHAM Centre for Pet nutrition and I would like to thank both organisations for this financial support. I would also like to thank the people at WALTHAM and MARS Fishcare for their help and engagement in Chapters 6-8 of my thesis. Particularly, thank you to my supervisor at WALTHAM, Dr Donna Snellgrove, for ethical advice many times, for arranging visits to MARS Fishcare and WALTHAM, supporting my attendance at the Lindau Nobel Laureate Meeting 2011 and enabling me to carry out GCMS work in the laboratories at WALTHAM. I am also very grateful for the hospitality of Gary Jones and his wife Kate, as well as the Research and Development team at MARS Fishcare in Chalfont (PA, USA): the trip was extremely rewarding both professionally and personally. Thanks also to Lewis Jones and Matt Talbot at WALTHAM for help with the GCMS. Without the organisational help of Ryan Mohammed (University of the West Indies) and his parents’ hospitality research in Trinidad and Tobago would have been impossible. I am also indebted to Andy Shinn and Beppe Paladini (Institute of Aquaculture, Stirling) for an extremely fruitful collaboration when describing Ieredactylus rivulus; thank you for hosting me in your laboratories. Thanks also go to Catrin Williams for her help with Spironucleus vortens, Jo Randall for R advice, Drs Mireille Johnson and Patricia Faria for help with molecular techniques and Dr. Gabrielle Archard for discussions on fish behaviour. Without the practical help of project students, research assistants, IASTE students and our gem of an animal technician much of this work would not exist: Emma Gillingham, Zalina Ali Bashir, Mari Palmer, Amanda Trask, Jo James, Brazilian Jacqui, Sarah Müller and Linda Erlandsson. CRIPES and the Cable Lab; thank you for being such an inspiration and a great group to be part of! On a more personal note, I would like to thank Madeleine, Sigrid, Ashley, Michi, Linda, Catrin, JoJ, Gabrielle, Louis and Layla. Danke Mama, Papa, Stephan, Sarah, für das Vertrauen und den Glauben an mich, selbst wenn ihr nicht immer verstanden habt, was ich mache und warum. Lastly, Richy, thank you so much for being my anchor, believing in me when it was most needed, grounding and supporting me through it all! V CONTENTS DECLARATION........................................................................................................................... II ABSTRACT.................................................................................................................................... IV ACKNOWLEDGEMENTS.......................................................................................................... V CONTENTS.................................................................................................................................... VI LIST OF TABLES......................................................................................................................... XI LIST OF FIGURES....................................................................................................................... XV CHAPTER 1: GENERAL INTRODUCTION............................................................................ 1 1.1 Infectious disease in aquatic environments........................................................................... 1 1.2 Parasite life histories: How do reproduction and transmission contribute to disease persistence and epidemics?................................................................................................... 2 1.3 Infectious disease and its control in food fish and ornamental aquaculture......................... 3 1.4 Integrated infectious disease management and chemical control......................................... 4 1.5 Gyrodactylids........................................................................................................................ 5 1.6 Treatment of gyrodactylid infections in fish......................................................................... 6 1.6.1 Problems with existing treatments.............................................................................. 6 1.6.2 Manual removal of gyrodactylids............................................................................... 9 1.6.3 Summary..................................................................................................................... 10 1.7 The host-parasite system: Gyrodactylus turnbulli and G. bullatarudis infecting common guppies (Poecilia reticulata)................................................................................................. 10 1.8 Thesis aims and hypothesis.................................................................................................. 11 1.9 References............................................................................................................................
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