Keeping things under control; diagnostic tools, control strategies and treatments of infectious diseases in freshwater fish

Fish is one of the most important protein sources for human diet. To meet the increasing protein demands of a rising human population, aquaculture has become a rapidly growing food-producing sector. The industry, though, faces many challenges, arguably the most important being infectious diseases, causing reduced productivity, sustainability and economic viability. Management of infectious diseases in fish farms is complex and requires a combination of approaches: prevention, surveillance, diagnosis and treatment to maximise yield. This thesis utilises a well-established model system, Gyrodactylus turnbulli – guppy (Poecilia reticulata), to investigate diagnostic tools and control strategies of infectious diseases in freshwater fish. Firstly, biological clocks of guppies and gyrodactylids were studied and infection was found to alter rhythmic activity of fish, resulting in nocturnal restlessness. Rhythmical variances in host and parasite behaviour and activity have the potential to be used for diagnosis and improved application of treatments. Next, the use of natural treatments, such as garlic and other essential oils, against parasitic diseases was investigated and even though efficacy depended on type, source and dose of ingredient, these herbal remedies reduced infection loads by at least 30%. To understand how these natural treatments work, for the first time, the proteomics of skin tissue of Gyrodactylus infected guppies was analysed. Protein expression varied with infection status of fish (susceptible, responding or resistant) ranging from no evidence of immune expression to programmed cell death and activation of the immune response. Finally, a questionnaire survey was designed regarding treatments of infectious diseases in ornamental freshwater fish. Data collected from 350 participants highlighted the different choice, use and application of treatments selected by hobbyists, retailers and researchers. Retailers followed a stricter approach taking every precautionary step to contain the effects of infection and minimise economic losses, whereas hobbyists relied more on natural treatments and botanicals for infectious diseases. Furthermore, various factors such as transport, time of day and water quality, that are known to impact efficacy of treatments were found to be closely monitored, in order to maximise treatment efficacy. Together, these results further the understanding of host-parasite dynamics and pave the way for new approaches and techniques to deal with the devasting effect of infectious diseases on aquaculture