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PhD Studentship - Evaluation of the susceptibility of English and Welsh salmonids to Gyrodactylus salaris - FC1183

The notifiable pathogen Gyrodactylus salaris (Malmberg, 1957) is highly pathogenic to Atlantic salmon, Salmo salar L. G. salaris (Gs) has been demonstrated to be responsible for the catastrophic decline of salmon stocks in more than 40 Norwegian rivers (Mo, 1994). Dolmen (1987) and Mo (1994) estimated that the impact of Gs on juvenile salmon in Norway and the subsequent decline in returning salmon accounted for a loss of up to 520 tonnes (20% of the total catch) per year. Gyrodactylid surveys conducted in the UK in the 1990s (Platten, McLoughlin & Shinn, 1994; Shinn et al., 1995,) and ongoing government-based surveillance programmes suggest that the UK is currently free of Gs. However, the potential for the parasite to cause similar impacts in the UK remains a real concern as the experimental exposure of native British salmon to Gs in Norway demonstrated that UK salmon stocks are susceptible (Bakke & MacKenzie, 1992). On a European scale, Gs is now known to be present in 11 European countries, most recently Poland (Rokicka, Zietara, Lumme & Skorkowski, 2007) and Italy (Paladini, Fioravanti, Hansen & Shinn, in prep), introduced, it is believed, through the movement of rainbow trout (Oncorhynchus mykiss). Within Italy, Gs has been found in multiple rainbow trout sites and analysis of archive material would suggest that it has been resident there for at least seven years, during which time it has not been detected in diagnostic samples.
Current national contingency plans in the UK assume that the dynamics of Gs infection on native English and Welsh salmonids will follow those already modelled in Scandinavia. These Scandinavian studies suggest that Atlantic strains of salmon are susceptible to infection,that grayling (Thymallus thymallus) are innately resistant but Gs can survive and reproduce on Scandinavian grayling for up to 140 days. Charr (Salvelinus alpinus) respond in a manner similar to grayling, with Gs surviving for up to 200 days; powan (Coregonus laveratus) are relatively resistant and brown trout are entirely resistant to infection.
Some native English and Welsh salmonid stocks have, however, been isolated from their Scandinavian counterparts since before the last glaciation and have accumulated many genetic differences over that time. How these stocks will respond to Gs is unknown.If we are to be assured that the UK's current contingency plans will be effective in the event of an introduction of Gs, it is imperative that the information used to formulate those plans is based on fact, not conjecture. There is therefore an urgent need to establish the susceptibility of English and Welsh populations of brown trout (Salmo trutta) and grayling, among other salmonids to Gs. If this work is not carried out and it is later shown that native salmonids are susceptible to Gs it could require major redrafting of this would invalidate all existing national contingency plans.
We currently know little regarding the effect of water chemistry on the dynamics of Gs infection. Aluminium sulphate has proved efficient in laboratory experiments as treatment against Gs infections (Poleo et al., 2004) and is currently being explored as a means of controlling Gs in the wild in Norway. In the study by Poleo et al. (2004) zince, manganese and copper were also tested and found to have similar impacts on the dynamics of infection. Also, very low levels of other toxicants like a nominal dose 5ug/l cadmium as typically found in drinking water can exert demonstrable effects on population growth of other species of Gyrodactylus (Carter, Shinn, Gibson & Sommerville, in prep). However, we know nothing of the impact of other water minerals and contaminants. Much of the existing work on the infection dynamics of Gs on a range of hosts (and on which UK contingency plans have based their assumptions) has been conducted within a single research facility using several strains of Gs but in water of a single composition. Scandinavian data collected by Karlsson et al. (2003) appear to suggest that the population dynamics of identical Gs strains on identical salmon strains can vary depending on experimental conditions. Therefore, when a protocol was designed to mimic conditions in the wild, (e.g. by considering water quality, light regimes and feeding) infection results appeared to be different to those obtained following the long-established Oslo protocols. The underlying mechanisms contributing to the difference in results under different experimental regimes have not been identified, and there is a need for further study to examine these issues in more detail. However, the preliminary data illustrate the potential danger in extrapolating too widely from a limited range of experimental data.
This PhD studentship proposal, will make a significant contribution to national Gs contingency planning by determining the responses of different strains of pathogenic Gs on different English and Welsh salmonids to pathogenic strains of Gs. The study also aims to assess the extent to which laboratory conditions might affect the results of infection experiments, and gauge whether extrapolation from existing results is appropriate for UK contingency planning. Data resulting from the project will contribute to existing Defra funded projects such as FC1177 ("Development of a risk evaluation system for the establishment of G. salaris in English and Welsh river systems") by highlighting river systems of greatest potential risk (in terms of hosts and water composition appropriate for supporting infections should Gs be introduced).
There are three main objectives to the proposed programme of work.

1. To assess the susceptibility of English and Welsh salmonids to G. salaris (15 months)

Current UK contingency plans are based on the assumption that British stocks of Atlantic salmon (S. salar) are susceptible to G. salaris, that brown trout (S. trutta) are resistant to infection, and that grayling (T. thymallus) and charr (S. alpinus) are relatively resistant. The first objective aims to determine whether these assumptions are correct. This will be achieved by transporting selected English and Welsh salmonids to Norway and conduct experimental challenges using a strain of G. salaris known to be pathogenic to Norwegian salmon. The experiment will be carried out in a research facility using Oslo water and will include appropriate susceptible Norwegian salmon strains as a control. The implications of any deviations from expected patterns of salmonid susceptibility will be discussed with regard to the reformulation of national contingency plans.

2. To investigate the population growth of G. salaris under field and laboratory conditions (9 months)

UK contingency plans are currently based on a large number of experimental studies conducted within Scandinavia. These include the implicit assumption that the responses, in terms of the pattern of G. salaris infection and population growth, observed in the laboratory environment accurately reflect the dynamics of infection in the wild. If the experimental data is to be used to inform national contingency planning, then it is imperative that this assumption is investigated further. This objective aims to achieve this by carrying out infection trials of susceptible Norwegian salmon strains in an experiment which more accurately reflects wild conditions, particularly with respect to the chemical composition of the water. An appropriate infected river site will be chosen and results will be compared with data collected by following the standard experimental protocol using Oslo water.

3. To conduct further G. salaris-based experimentation in support of UK contingency planning (12 months)

The precise research activities in the third phase of this project will depend on the research findings of Objectives 1 and 2 of this project. Experiments will be designed in consultation with the project partners in Cefas and Defra to address the most pressing issues that are needed in the construction of a robust contingency plan for England and Wales.
Project Documents
• EVID4 - Final project report : FC1183 EVID4 Final Report   (373k)
• FRP - Final Report : FC1183 EVID4 Final Report 8 Project Report to Defra   (662k)
Time-Scale and Cost
From: 2008

To: 2012

Cost: £89,836
Contractor / Funded Organisations
University - Stirling
Fish Disease              
GS (Gyrodactylus Salaris)              
Fields of Study
Fish Health and Aquaculture