Push-pull strategies: combination control of fish pathogens

Aquaculture is the world’s fastest growing food sector with fish now the most important source of protein for humans. Wild fisheries are rapidly reaching sustainable harvest limits and there is increasing pressure on aquaculture to increase production yields. One of the greatest global challenges facing both farmed and wild fish is infectious disease, which causes substantial economic losses to aquaculture and fisheries. Fish lice are a particular problem worldwide. Marine (incl. Lepeophtheirus salmonis and Caligus elongatus) and freshwater (Argulus spp.) lice cause major epizootics leading to mass fish mortalities. Even mild lice infections cause condition loss, migration failure and long term declines of fishery performance (EA 2005). Sea lice have been most intensively studied because of their global impact on farmed salmon (Costello 2009), but despite this research spanning decades, sustainable control is still out of reach, partly hampered by the cost and problems of working with large marine fish. Argulus species, on the other hand, can be maintained relatively easily on a range of host species. The most common species, A. foliaceus infects both economically and ecologically important fish species (Fig. 1) with recent epidemics in southern England and Wales causing an estimated loss of £5 M annually in trout fisheries alone. Lice resistance to drugs is rising and coarse fisheries with resident fish have limited options for stock management. The absence of effective control measures has also fuelled the illegal use of environmentally damaging chemicals in efforts to reduce financial losses. Using stickleback- and carp-Argulus systems, this PhD will use a novel combination approach to understand the basis of host preference by investigating both deterrents and attractants of infection.

Trapping of pests often employs a "push-pull strategy" whereby pests are "pushed" off their hosts via repellents and then "pulled" into traps via attractants (Fig. 1E). Using state-of-the-art methods applied to agricultural pests, the student will assess (1) the distribution of Argulus epidemics in UK waters in relation to climatic conditions, (2) whether chemicals can increase detachment of Argulus from the host, (3) the effectiveness of lice, host and physical attractants, and (4) how deterrents and attractants in combination might reduce infection and increase trapping success via the push-pull strategy. The student will develop skills in GIS, modelling, experimental parasitology, fish behaviour, pharmacokinetics and chemical analysis of semiochemicals. The project will increase our knowledge of Argulus-host interactions, as well as providing practical advice to fish managers on how to reduce the impact of these pathogens