Circadian rhythms are timekeeping mechanisms responsible for an array of biological processes. Disruption of such cycles can detrimentally affect animal health. Circadian rhythms are critical in the ...co-evolution of host–parasite systems, as synchronization of parasite rhythms to the host can influence infection dynamics and transmission potential. This study examines the circadian rhythms in behaviour and activity of a model fish species (Poecilia reticulata) in isolation and in shoals, both when uninfected and infected with an ectoparasite (Gyrodactylus turnbulli). Additionally, the rhythmical variance of parasite activity under different light conditions as well as rhythmical variance in parasite transmissibility was explored. Overall, infection alters the circadian rhythm of fish, causing nocturnal restlessness. Increased activity of gyrodactylids on the host's skin at night could potentially contribute to this elevated host activity. Whilst migration of gyrodactylids across the host's skin may have caused irritation to the host resulting in nocturnal restlessness, the disruption in guppy activity rhythm caused by the expression of host innate immunity cannot be excluded. We discuss the wider repercussions such behavioural responses to infection have for host health, the implications for animal behaviour studies of diurnal species as well as the application of chronotherapeutic approaches to aquaculture.
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.
