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Interaction of Disease and Temperature on the Aerobic INTERACTION OF DISEASE AND TEMPERATURE ON THE AEROBIC SCOPE OF FRESHWATER FISH AND IMPLICATIONS FOR CHANGING CLIMATES Emily Lawlor BSc. This thesis is presented for the Honours Degree in Conservation and Wildlife Biology, School of Veterinary and Life Sciences, Murdoch University, 2016. DECLARATION I declare that this thesis is my own account of my research and contains as its main content work which has not been previously submitted for a degree at any tertiary education institution. EMILY LAWLOR ABSTRACT Climate change is a major threat to both freshwater and marine ecosystems on a global scale. There is evidence that for aquatic pathogens and parasites, increasing water temperatures will favour increasing transmission rates and virulence. Increasing water temperature may stress fish and transiently compromise the immune system, exacerbating the effects of infection. The high energy costs of an upregulated immune response will have consequences on other physiological processes such as growth and reproduction. In order to study the effects of temperature on pathogenicity, a bioassay to challenge the Australian native freshwater pygmy perch, Nannoperca vittata with a bacterium Photobacterium damselae damselae was carried out. The bioassay was carried out at two temperatures; 17°C, thought to be the optimum for fish survival and growth, and 28°C, presumed to be approaching the upper critical limit for the species. Nannoperca vittata was found to be susceptible to infection by P. damselae damselae, the first time that infection has been demonstrated in native Australian freshwater fishes. The effect concentration that caused mortalities in 50% of the population (EC50) was lower at 28°C (4.82x105 CFU ml-1) than at 17°C (2.81x106 CFU ml-1). Fish mortalities were significantly greater and times to death were significantly shorter at 28°C than at 17°C and this is the first time that this has been demonstrated experimentally for P. damselae damselae. Following the pathogenicity trial, the aerobic scope of exposed versus non-exposed pygmy perch of both 17°C and 28°C experimental groups was determined in a respirometer. Aerobic scope is defined as the difference between maximum metabolic iii rate and standard metabolic rate. The aerobic scope was greater in exposed than in unexposed fish at 17°C and conversely, greater in unexposed than in exposed fish at 28°C.. This difference occurred because standard metabolic rate increased with exposure at both temperatures, whereas maximum metabolic rate increased at 17°C, but not at 28°C. The increase in standard metabolic rate at both temperatures was expected as a consequence of an upregulated immune response following exposure to the bacterium. The difference in maximum metabolic rate is hypothesised to be a consequence of a compensatory increase in oxygen carrying capacity, which is counteracted by a persistent immune response at 28 but not at 17°C. This hypothesis requires further testing. The results from this study suggest, firstly, that fish are less tolerant of infection at higher water temperatures and secondly, that a combination of higher water temperature and increased exposure to pathogens may decrease aerobic scope and therefore fitness. This study showed that higher temperatures decrease aerobic scope in fish, thus suggesting that rising temperatures with global warming may have the same effect. This is the first study to demonstrate such a response in an Australian native freshwater fish. Further research in this field is urgently required to enable conservation management plans that address the threats posed to native freshwater fish species through climate change. iv TABLE OF CONTENTS ABSTRACT ............................................................................................................................ iii TABLE OF CONTENTS ......................................................................................................... v ACKNOWLEDGEMENTS .................................................................................................. vii LIST OF FIGURES ............................................................................................................. viii LIST OF TABLES ................................................................................................................. xi 1. INTRODUCTION ................................................................................................................ 1 1.1 Conservation of freshwater fishes ....................................................................... 1 1.1.1 Global freshwater fish diversity ........................................................................... 1 1.1.2 Australian freshwater fish diversity ..................................................................... 1 1.1.3 Conservation status of freshwater fishes.............................................................. 4 1.2 Effects of climate change on freshwater biodiversity ........................................ 7 1.2.1 Climate change in south-western Australia ......................................................... 9 1.2.2 Effects of climate change on freshwater fishes .................................................. 11 1.3 Direct effects of increasing temperature on physiological processes.............. 11 1.4 Indirect effects of increasing temperature on infectious disease .................... 18 1.4.1 Effect of temperature on pathogen reproductive rate and virulence ................. 19 1.4.2 Effect of temperature on host immunocompetence ............................................ 21 1.5 Synergistic effects of increased temperature and infectious disease on freshwater fishes ........................................................................................................ 24 1.6 Research aims ...................................................................................................... 26 2. MATERIALS AND METHODS ...................................................................................... 28 2.1 Collection and maintenance of fish .................................................................... 28 2.2 Production of bacterial challenge materials ..................................................... 28 2.3 Pathogenicity trial ............................................................................................... 29 2.3.1 Experimental design ........................................................................................... 29 2.3.2 Data analysis ...................................................................................................... 30 2.4 Respirometry trial ............................................................................................... 32 2.4.1 Experimental design ........................................................................................... 32 2.4.2 Measurement of SMR and MMR ........................................................................ 33 2.4.3 Data analysis ...................................................................................................... 34 3. RESULTS ........................................................................................................................... 37 3.1 Pathogenicity trial ............................................................................................... 37 v 3.2 Respirometry trial ............................................................................................... 43 4. DISCUSSION ..................................................................................................................... 48 4.1 The effect of temperature on the pathogenicity of Photobacterium damselae damselae to Nannoperca vittata ................................................................................ 48 4.2 The effect of temperature and exposure to Photobacterium damselae damselae on the metabolic rate and aerobic scope of Nannoperca vittata ............ 53 4.2.1 The effect of body mass on SMR, MMR and AS ................................................. 53 4.2.2 The effect of temperature on SMR, MMR and AS .............................................. 54 4.2.3 The combined effects of temperature and pathogen exposure on SMR, MMR, and AS ......................................................................................................................... 57 4.3 Implications for the conservation of freshwater fishes in south-western Australia ..................................................................................................................... 61 4.4 Limitations and future research ........................................................................ 62 5. CONCLUSION ................................................................................................................... 66 6. REFERENCES ................................................................................................................... 67 vi ACKNOWLEDGEMENTS I wish to take this opportunity to express my gratitude to my three supervisors Alan Lymbery, Stephen Beatty and Adrian Gleiss, from the Freshwater Fish Group and Fish Health Unit at Murdoch University, for without their support this thesis would not have been possible. These three lads have helped me through all the bumps in the road and I would like to thank you for your time, generosity, shared knowledge and for just being down to earth people whose doors are always open. I would also like to thank Ph.D. student Siew Mee Bong for her constant jokes and help for the many hours
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