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Infectious disease and changing climates: Quantifying threats to freshwater fish from multiple stressors

Bong, Siew Mee (2020) Infectious disease and changing climates: Quantifying threats to freshwater fish from multiple stressors. PhD thesis, Murdoch University.

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Australia has a highly endemic freshwater fish fauna that is threatened by climate change and a number of other anthropogenic processes. Climate change represents a major threat to freshwater fishes, directly through increasing water temperature and decreasing water flow, and indirectly by exacerbating existing stressors, such as infectious disease. This study investigated the interactive effects of increasing water temperature and infectious diseases on two freshwater parasite/host systems: (1) western pygmy perch, Nannoperca vittata, an endemic temperate species to south-western Australia, infected with the bacterium Photobacterium damselae damselae; and (2) guppy, Poecilia reticulata, an introduced subtropical species, infected with Streptococcus iniae. Bacterial pathogenicity and growth rate, and fish metabolic rate and immune response, were measured over a range of temperatures between 16 and 28°C. The virulence of both P. damselae damselae to N. vittata and S. iniae to P. reticulata increased with temperature, being greatest at 28°C. Increasing water temperature, over the range from 16 - 28°C, also increased the in vitro population growth rate of both bacterial species, but over the same temperature range, there were contrasting effects on the immune response of the two host species. For N. vittata, when challenged with P. damselae damselae, the increase in respiratory burst activity and lysosome content was greatest at 17°C, while for P. reticulata challenged with S. iniae, the increase in these two immune parameters was greatest at 28°C. Exposure to bacterial infection increased both standard metabolic rate (SMR) and maximum metabolic rate (MMR) in N. vittata and P. reticulata, being greatest at lower temperatures (17°C) for N. vittata and at higher temperatures (24°C) for P. reticulata. The increase in MMR with exposure to bacteria, most marked in N. vittata, was unexpected and warrants further investigation. These data suggest that increasing water temperatures as a result of climate change may produce a thermal mismatch in performance between native freshwater fish species and their bacterial parasites.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): Environmental and Conservation Sciences
United Nations SDGs: Goal 13: Climate Action
Goal 14: Life Below Water
Supervisor(s): Lymbery, Alan, Beatty, Stephen and Gleiss, Adrian
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