Life history, distribution and invertebrate host-parasite interactions of the causative agent of proliferative kidney disease (PKD), Tetracapsuloides bryosalmonae
التفاصيل البيبلوغرافية
العنوان:
Life history, distribution and invertebrate host-parasite interactions of the causative agent of proliferative kidney disease (PKD), Tetracapsuloides bryosalmonae
Proliferative kidney disease (PKD) is an emerging disease of salmonid fish that is linked with environmental change. The causative agent is the myxozoan Tetracapsuloides bryosalmonae (Tb) which exploits the freshwater bryozoan Fredericella sultana (Fs) as definitive hosts. Fs forms colonies that reproduce mainly asexually through fragmentation and the production of over-wintering dormant stages (statoblasts). In Fs the parasite cycles between overt and covert infections, the former characterised by sacs containing spores infectious to fish. This thesis aims to increase understanding of the prevalence, severity and transmission of Tb in Fs through field and laboratory studies and to identify factors associated with the presence and abundance of the parasite and its hosts in British rivers. The results of this research are ultimately relevant for the conservation, health and diversity of wild fish populations. I provide an introduction to Tb and PKD and follow with four data chapters on infection dynamics of Tb within bryozoan hosts and its detection in river water. A fifth data chapter investigates factors affecting the distribution and abundance of Fs and Tb and the identification of disease risks. A concluding chapter summarises the salient points of my research and suggests directions for future work. My research has demonstrated: high prevalence of covert infections in bryozoan populations in space and time (Chapter 2); transmission to colony fragments and statoblasts via cryptic stages (Chapter 3); the quantification of Tb in water samples in early summer and a greater detection of Tb in larger sample volumes (Chapter 4); that host stress promotes horizontal transmission from bryozoans to fish (Chapter 5); that Fs is more likely to occur in warm, eutrophic habitats in the south of Britain (Chapter 6).
