Edinburgh Napier University

  In 2005, Atlantic salmon (Salmo salar L.) migrating to the United Kingdom exhibited swollen, haemorrhagic vents, symptoms not previously recorded. The condition was latterly termed Red Vent Syndrome (RVS), and subsequently observed across the North Atlantic. RVS has been pathognomonically associated with one of the most abundant parasites within the marine environment, the ascaridoid nematode Anisakis simplex, which also causes Anisakiasis in humans. Although A. simplex is commonly found in Atlantic salmon, heavy infestation of the vent region is novel, and the expression of RVS has not been prevalent in other fish species. Red Vent Syndrome has been well studied, however, the causes of the condition, and the reasons driving the novel site of infestation exhibited by A. simplex, have not been clarified. The aim of this PhD therefore, is to provide new information regarding the underlying factors of the infestation of the vent region by A. simplex, and the emergence of RVS. This study therefore: i) assessed the relationship between nematode burdens within the viscera and musculature, in comparison to the vent in 117 adult Atlantic salmon; ii) compared the genetic structure of A. simplex present in the vent region and the viscera using the entire nuclear internal transcribed spacer (ITS) region; iii) investigated migratory route and feeding ground of Scottish salmon populations using stable isotope analysis of dorsal muscle tissue and parasite component communities and, iv) assessed the expression of the cytokine TNF-α1 within vent muscle tissue using (q)RT-PCR, in relation to RVS severity. Phylogenetic analyses have shown that it is A. simplex sensu stricto infesting the vent region. The results show that there is a significant positive relationship between the nematodue burden in the body (viscera and musculature) and in the vent region. Isotopic signatures of salmon populations showed no significant differences, however, A. simplex intensities between populations on the East and North coasts of Scotland suggest geographical differences in A. simplex transmission pathways. Finally, the expression of TNF-α1 is not significantly different between RVS severity, and nematode burden. Out of the four studied factors, increasing nematode intensities in Atlantic salmon populations, and the significant positive relationship of nematode intensities between the body (viscera and musculature) and the vent, are likely to explain the infestation of the vent by A. simplex. The underlying causes of RVS however remain uncertain and require further research. With incidences of RVS observed across a number of populations over a large spatial area, regional and global effectors such as warming sea surface temperatures, and the North Atlantic Oscillation are expected to play key roles in its aetiology.