FUTUREFISH: The role of circadian rhythms, immunity and infection in enhancing aquaculture

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There is a rapidly increasing global demand for fish, yet stagnation and collapse of traditional capture fisheries, therefore aquaculture (fish farming) must be expanded and intensified to meet demand. Currently, the principal barrier to aquaculture development is disease; causing devastating economic losses and increasing reliance on drug interventions. Indoor fish farming provides hope for intensification of aquaculture; finely controlling environmental conditions to maximise fish production without encroaching on natural aquatic habitats. However, while manipulated light regimes (extended day lengths or even continuous light) are often used in indoor aquaculture to improve rearing, it is unknown how such approaches contribute to disease issues. Across all forms of life; from microbes to humans, organisms exhibit daily cycles in biological processes such as behaviour and metabolism, known as circadian rhythms. Circadian rhythms are typically controlled by expression patterns (turning on and off) of "clock" genes; a system often referred to as the molecular body clock. Molecular clocks can be altered or "entrained" to light conditions. Body clocks and circadian rhythms are important to immune system functioning; levels of immune cells and the ability to fight infection varies by time of day in mammals. Moreover, disruption of circadian rhythms (e.g. shift-work, jet-lag) can increase susceptibility to or severity of disease in humans. Therefore, the characterisation of fish circadian rhythms of immunity and the examination of how light regimes affect fish disease resistance is vital to future sustainable improvement of aquaculture methods. In addition, although it is well known that parasites too exhibit daily rhythms, we do not yet know the nature of their molecular body clocks. Therefore, to fully understand the daily interplay between hosts and their pathogens, be it fish or other animals, we must also consider the control of rhythmicity in parasites.Working at Cardiff University, bringing together world leaders in fish parasitology, invertebrate genetics, and microbial communities, and in collaboration with experts in molecular clocks at Aberystwyth University, I will address these key knowledge gaps in the circadian biology of fish-parasite interactions. I will measure the impact of three economically-important parasites (Argulus; freshwater louse, Gryodactylus; skin worm, Saprolegnia; water mould) on rainbow trout circadian rhythms of clock and immune gene expression, and determine how light regimes alter the susceptibility of trout to infection. It is predicted extended and/or constant photoperiods increase susceptibility to disease. In addition, I will quantify the circadian rhythms of gene expression in Gyrodactylus and couple the findings with measures of parasite activity and infection ability. I hypothesise rhythmicity of key genes related to parasite infection ability, coupled with daily variations in host immune levels, drive circadian rhythms in parasite survival and behaviour on-host. Finally, I will determine whether the microbiome (bacteria community) of trout skin exhibits circadian rhythmicity and examine how perturbation, via antibiotic treatment, impacts the skin's microbial composition and subsequent susceptibility to parasites. It is predicted reduced variation in beneficial skin microbes due to antibiotics will increase susceptibility to parasites. Harnessing the power of optimal circadian rhythms can improve health and reduce antimicrobial usage in aquaculture. Taken together, the results of this fellowship will provide important new insights to inform fish farm management practices and fundamentally advance the understanding of daily interactions between parasites and their hosts.