Host - parasite interactions between Lernaeocera branchialis (Copepoda: Pennellidae) and its host Gadus morhua (Teleosti: Gadidae)

• Main Author: Barker, Sarah E.
• Other Authors: Bron, James Emmanuel, Thompson, Kimberly Dawn, Bricknell, Ian R., The Fisheries Society of the British Isles, School of Natural Sciences, Aquaculture
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Stirling 2009
• Subjects: Lernaeocera branchialis; Gadus morhua; host-parasite interactions; immune response; Copeda; Fish Parasites; Atlantic cod; Host-parasite relationships; atlantic cod
• Online Access: http://hdl.handle.net/1893/1792; http://dspace.stir.ac.uk/bitstream/1893/1792/6/BarkerSE2009%20thesis.pdf

Abstract Lernaeocera branchialis (Linnaeus, 1767) is a parasitic copepod possessing a complex dual-host lifecycle. The “definitive” gadoid hosts, including Gadus morhua (Atlantic cod), Melanogrammus aeglefinus (haddock) and Merlangius merlangus (whiting), are infected by the fertilised female, which penetrates the host’s ventral aorta or bulbus arteriosus whilst undertaking extensive metamorphosis and a haematophagous lifestyle. The pathogenic effects of this activity upon the host have been well documented and mortality may occur, especially when multiple parasites are present. These negative impacts on cod, particularly juveniles, by L. branchialis have the potential to adversely affect cod aquaculture in the future, and already vulnerable wild cod stocks. This PhD project therefore, investigated the immune response of wild haddock and cultured-cod post-infection by L. branchialis, and the possible mechanisms by which the parasite modulates / evades the host’s immune response. The systemic immune response of both wild haddock and cultured-cod post-infection by L. branchialis depended on the maturation stage of the parasite, and in the former host species, upon the infection intensity. Wild haddock harbouring fully metamorphosed females showed an increase in circulating thrombocytes and a decrease in serum protein levels however; if multiple mature L. branchialis were present the haddock possessed reduced circulating monocytes, and increased circulating thrombocytes and serum anti-trypsin activity. Infection by L. branchialis was also associated with a suppressive effect on haddock serum spontaneous haemolytic activity. These responses were thought to be due to the host trying to counteract the increased damage caused by the massive increase in size and the feeding of the mature parasite, which is more pronounced when multiple parasites are present, resulting in the increase in some parameters and the ‘consumption’ of others. However, the effect of parasite-derived secretions and other pathogens due to ...