This study investigates the life cycle of Sphaerospora truttae, a myxozoan parasite of the Atlantic salmon, using molecular methods based on the 185 rONA. DNA sequencing showed that the 185 rONA of S. truttae differs substantially from the sequence obtained from its proposed alternate actinosporean life cycle stage, Echinactinomyxon type 5. With more than 90% sequence identity Echinactinomyxon type 5 is closely related to Myxobolus portucalensis whereas S. truttae with an extraordinary long 185 sequence (2541 bp), with inserts in the variable regions of the gene, does not relate closely to any myxozoans. On the basis of the obtained sequence for S. truttae, a single round nested peR assay was developed which allows low-level detection and specific identification of S. truttae in all life cycle stages. Furthermore, two of the primers from the peR assay were successfully used on tissue sections in an optimised in situ hybridisation (ISH) protocol. ISH experimentally identified the gills as the predominant entry locus of S. trottse into the fish host and it detected the spatiotemporal migration of the parasite via the vascular system into the target organ, the kidney. The ISH protocol and the peR assay were also used to screen oligochaetes and other co-occurring invertebrates for S. truttae infection but an alternate host for S. truttse could not be identified. However, 12 actinosporean stages were found and they were characterized on the basis of their 185 rONA, together with 9 further myxosporean species from wild fish in the same riverine habitat. Three actinosporeans were found to be genetically identical with three myxosporeans (Myxidium truttae, Chloromyxum truttse and Chloromyxum sp.) and thus represent alternate life cycle stages of these species. Phlyogenetic analysis of the myxozoans identified a very basal position of S. truttae and S. elegans, as a sister group to the marine species. All other species were nested in the freshwater clades and clustered according to host tissue localization, but independent from host species or myxozoan spore taxonomy.

Rapid advances in the aquaculture industry pose an environmental challenge that is generated by outbreeding between escaped domesticated and wild individuals. Given that escapees genetically differ from wild individuals because of domestication and possibly by ancestry, periodic domesticated-wild outbreeding has the potential to influence fitness-related traits in wild populations. In Atlantic salmon (Salmo salar), the understanding of mechanisms and direction of domesticated influences are especially important because of the conservation concerns associated with many wild populations, notably in the southern parts of their North Atlantic range. My thesis investigates domestication-induced, genetically based changes during the parr stage by assessing growth, parr maturity and survival under predation for three salmon strains differing in their history of domestication, as examined in two semi-natural environments (predator present, absent). Growth and size-at-age increased with increasing generations of domestication, yet male parr maturation probability declined. Survival under gape-limited predation increased with domestication-conveyed increases in size and growth rate. Domesticated but not wild individuals exhibited stress-resistant growth in the presence of a predator. To assess mechanism and magnitudes of trait changes resulting from domesticated-wild outbreeding, a domesticated strain was crossed with a wild population (up to third-generation hybrids) and outbreeding effects were studied for different life stages, several controlled environmental laboratory conditions, and traits. Life stages included the developmental periods between egg and fry, and between immature and adult post smolts. Traits assessed included survival, yolk conversion efficiency, size-at-age, maturation probability, growth rate, mRNA transcript levels and their environmental plasticity. For many traits, both additive and non-additive genetic components in the between-population genetic architecture were revealed by cross means analyses. Furthermore, maternal outbreeding effects on early life stages were present. Altogether the results indicate that constant outbreeding effects of escapees on wild populations will increase present growth rates during all life stages and decrease early maturation probabilities for male parr and post-smolts, but by unpredictable magnitudes across hybrid generations. Maternally controlled co-adapted traits might be disrupted in hybrid mothers. Further, mixed-origin individuals might be temporarily at an advantage relative to wild individuals because of size and growth advantages and these might accelerate a wild genotypes displacement.

A two-year study of the actinosporean fauna of oligochaetes was conducted at an Atlantic salmon fish farm located at the extreme north of Scotland. The actinosporean fauna and their morphological characteristics, the ultrastructural development of four different actinosporean collective groups, the epidemiology of all actinosporean types identified,the complete life cycle of Sphaerospora truttae, the circadian and seasonal spore release patterns of actinosporean types and the myxospores of S. truttae, the viability of actinosporeans and their responses to fish mucus were determined. Twenty one actinosporean types belonging to seven collective groups: Synactinomyxon (3 types), Aurantiactinomyxon (4 types), Echinactinomyxon (5 types), Raabeia (6 types), Neoactinomyxum (l type), Triactinomyxon (1 type) and Siedleckiella (1 type) are described. Six types were identified to previously described forms; Synactinomyxon "A" of McGeorge et al. (1997); Synactinomyxon tubificis Stole, 1899, S. longicauda Marques, 1984, Aurantiactinomyxon-type of McGeorge et al. (1997), Echinactinomyxon radiatum Janiszewska, 1957, Raabeia-type of McGeorge et ai. (1997). The remainder appeared to be new types of the collective groups. Temperature was found to have a significant effect on the spore morphology and caused statistically important differences in the spore dimensions, especially on the caudal processes. Synactinomyxon-type 1, Aurantiactinomyxon-type3, Echinactinomyxon-type5 and Raabeia-type4 were studied at the TEM level to determine the developmental stages of each type. All actinosporean types studied had uninucleate cells as the earliest stage of development. Formation of a subsequent binucleate cell stage was either due to the division of the nucleus in a uninucleate cell or the plasmogamy of two uninucleate cells. The earliest pansporocyst formation seen was two outer somatic cells surrounding two inner generative alpha and beta cells in all actinosporean types studied. However, the formation of an early pansporocyst followed a four-nuclei stage only in Raabeia. Subsequently, the number of somatic and generative cells increased as a result of mitotic divisions and reached 8 alpha and 8 beta cells at the end of the division stages. Echinactinomyxon had only four somatic cells in pansporocyst, whilst Synactinomyxon, Aurantiactinomyxon and Raabeia had eight. Following the copulation of each pair of alpha and beta cells, 8 zygotes were formed. Then, two mitotic divisions of each zygote resulted in a four-cell stage of each sporoblast. Valvogenesis and capsulogenesis was followed by the formation of 8 mature spores inside each pansporocyst. Over the two year sampling programme the overall infection prevalence of oligochaetes with actinosporeans was 2.9%. The infection prevalence was higher in the first year (3.3%) than the second year (2.3%). The infection prevalences of individual types were between 0.001% and 0.9%. Summer was the preferred season of spore release (4.1%), followed by autumn (2.9%) , spring (2.8%) and winter (1.6%), Some parasites such as Echinactinomyxon-typel released spores throughout the study period, whilst Synactinomyxon-type2 was recorded only in summer. There was also a positive relationship between the number of actinosporean types released and water temperature. A one year sampling programme also indicated that Sphaerospora truttae had two distinct life cycle phases, extrasporogonic and sporogonic, in the fish. Extrasporogonic stages were first detected at the beginning of July 1996 with a prevalence of 50% and were seen over an 8-10 week period. Sporogonic stages first became detectable in the kidney tubules at the beginning of September 1996. As well as sporogonic stages, many developing pseudoplasmodia were also observed at this time. Pseudoplasmodia were always present along with mature spores. The infection prevalence stayed above 80% throughout the period of infection. Experimental infections showed that Echinactinomyxon-type5, was the alternate life cycle stage of S. truttae in the oligochaete Lumbriculus variegatus. The time taken from the exposure of Atlantic salmon to Echinactinomyxon-type5 spores to formation of mature Sphaerospora truttae spores was 4.5 months (138 days). However, infections of Atlantic salmon with presporogonic and immature spores of S. truttae were first seen at 3.5 months post-exposure (110 days). In addition to S. truttae, the life cycle of Chloromyxum truttae was also completed at 4.5 months (138 days) post - exposure at 12-16°C using Aurantiactinomyxon-type4 spores released from Tubifex tubifex. Worms infected with Synactinomyxon-type 1, Aurantiactinomyxon-type I, Echinactinomyxon-type1 and type5, Raabeia-type4 and Neoactinomyxum-type showed inconsistent spore release patterns over five subsequent days at ambient temperatures. Up to 5000 spores an each day were released from infected worms with the exception of Echinactinomyxon-type5 which released up to 80,000 spores per day. Experimentally there was a positive relationship between the numbers of spores shed and water temperature. The spore release of worms infected with Synactinomyxon-type I, Aurantiactinomyxon-type 1, Echinactinomyxon-type I, Raabeia-type4 and Neoactinomyxum-type spores were also studied at 3 h intervals and showed that peak release occurred between 22.00 and 01.00 h. Studies on the spore release patterns of Sphaerospora truttae myxospores from Atlantic salmon showed that mature spores were first released at the end of November, peaked around April and then decreased sharply. Number of mature spores present in the kidney of the fish showed a similar pattern of abundance. Polar filaments of Echinactinomyxon-type I, Raabeia-type4 and Aurantiactinomyxon-type I spores discharged in response to mucus from Atlantic salmon, brown trout, 3-spined stickleback and common carp. However, the response to the mucus from each fish species was different. In each case majority of discharges occurred within the first 5 min of exposure to mucus although there were further discharges up to lh. The viability of Synactinomyxon-type I, Echinactinomyxon-type I, Raabeia-type4, Aurantiactinomyxon-typel and Neoactinomyxum-type spores had a negative correlation with increasing temperature. In general, the spores remained viable for 6-7 days at 4°C, 4-5 days at 13°C and 4 days 22°C.

Thesis (Ph. D.)--University of Rhode Island, 2003. / Typescript. Includes bibliographical references (leaves 172-184).

Thesis (M.Sc.) - Memorial University of Newfoundland, 1980. / Bibliography : leaves 64-72. Also available online.

Thesis (M.Sc.) -- Memorial University of Newfoundland. / Typescript. Bibliography : leaves 110-115. Also available online.

Thesis (M. Sc.), Memorial University of Newfoundland, 1999. / Bibliography: p.105-113.

Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on July, 1 2009). Includes bibliographical references.

Thesis (Ph.D.)--Aberdeen University, 2008. / Title from web page (viewed on July 20. 2009). Includes bibliographical references.

Thesis (Ph.D.)--Memorial University of Newfoundland, 2004. / Includes bibliographical references.