Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

This study examined three aspects of the processes of host location and initial attachment of the infective copepodid stage of the sea louse, <i>Lepeophtheirus salmonis</i> Krøyer 1838, to its host Atlantic salmon, <i>Salmo salar </i>(L.). The role of host and non-host odours and derived chemicals in modifying copepodid behaviour was identified in laboratory bioassays. Seasonal and stage-specific changes in the energetics of the eggs and the free-living larval stages were investigated through respiration experiments and chemical analyses. The influence of realistic physical factors, light intensity, salinity and host swimming speed, on determining the sites of initial copepodid attachment were identified in flowing water conditions, by the use of flume studies. Exposure to original odours and extracts of host odours resulted in significant changes in non-oriented behaviour and movement patterns which would increase the probability of host encounter, whilst exposure to original and extracts of host odour gave near-significant levels of oriented movement to the odour source. The host-derived chemicals isophorone and 1-octen-3-ol appeared to induce activated and limited arrested behaviours in the copepodid, respectively. During all stages of embryonic and larval development a gradual reduction in weight and energy content with developmental stage of larvae was noted, as lipid and protein stores were preferentially catabolised to provide energy for morphological changes and increased locomotion of the later larval stages, as revealed by an observed increase in respiration rates with developmental stage. Seasonal changes in embryonic dry weight, energy and biochemical composition were masked by the presence of seasonally variable proteinaceous egg cases. The free living stages showed a mixed trend in reproductive strategy, similar to previous studies of <i>L. salmonis </i>eggs in response to seasonal changes in temperature and photoperiod, but also similar to trends observed in food-unlimited holopelagic copepod species. Light intensity, salinity and host swimming speed independently and interactively altered the distribution and total initial attachment of <i>L. salmonis</i> copepodids on host Atlantic salmon smolts.

Thesis (M.S.) in Zoology--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 78-86).

Thesis (M.S.) in Microbiology--University of Maine, 2001. / Includes vita. Includes bibliographical references (leaves 52-59 ).

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.

Sequencing and phylogenetic analysis was used to characterise a number of Scottish IPNV isolates. The majority of isolates from Scotland were genetically closely related to the Sp strain of IPNV. There appears to be a link between the IPN status of a farm and the presence of IPNV in the environment but this is short lived as IPNV does not typically persist in natural reservoirs at sufficiently high levels to allow re-infection to occur. Real-time PCR was used to study the expression of a subset of immune relevant genes following IPNV challenges by a natural (co-habitation) and unnatural (i.p.) route. Differences were observed between the two challenge routes which may reflect orientation towards a Th1 or Th2/regulatory response in i.p. and cohabiting infected fish respectively. These results may give us a better understanding of immune regulation in Atlantic salmon, and may lead to improved vaccine development. Real-time PCR was used to analyse the expression of the two Atlantic salmon IRF-1 isoforms, the results show that the IRF-1 gene is induced in response to IPNV infection in kidney tissue and in ASK cells but in macrophages no significant difference in expression was observed. SSH identified several candidate genes that may be part of a protection mechanism in Atlantic salmon important for controlling viral replication and the pathogenic effects of IPNV. Genes that were found to be significantly up-regulated belong functionally to the following groups of processes: proteolysis immune and stress response, transcription/replication, translation, protein transport/protein interactions and the metabolism. This is the first report identifying Vig-2 as being upregulated by IPNV.

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

Thesis (doctoral)--University of Stockholm, 1983. / Includes bibliographical references.

Salmonid alphaviruses (SAV) are a group of viruses that have recently emerged as a serious threat to the salmonid aquaculture industry in Europe. Over recent years, diseases caused by SAV have severely hampered the Scottish, Irish and Norwegian Atlantic salmon industry, and are considered to be among the major economically important viral diseases affecting the industry at present. Amongst the six subtypes characterised so far, Salmonid alphavirus 1 (SAV1) causes severe pathology in the heart, pancreas and the skeletal muscle of Atlantic salmon leading to death and growth retardation in the affected fish. The biochemical characteristics of the virus and the sequential pathology of the diseases caused by SAV have been described; however the mechanisms responsible for causing the disease and the host defence mechanisms against the virus are poorly defined. This thesis therefore examined the pathogenesis of SAV infection at the cellular and molecular level in vivo in salmon and in vitro in salmonid cells, with a special emphasis on host immune defence mechanisms against the virus. SAV was first isolated from Chinook salmon embryo-214 (CHSE-214) cells in 1995 in Ireland. Several cell lines have since been used to grow the virus. In the present study, three established salmonid cell lines, Chum salmon heart -1 (CHH-1), CHSE-214 and Salmon head kidney -1 (SHK-1) were evaluated for their ability to support the isolation of SAV-1 from infected fish tissue, with CHH-1 cells giving the fastest cytopathic effect (CPE) during primary isolation. The CPE appeared as localised cell-rounding on CHH-1 and CHSE-214 cells, although in SHK-1 cells, the cells were seen to slough off the monolayer relatively later than with the other two cell lines during the infection. The host response to SAV infection was evaluated by experimentally infecting Atlantic salmon parr using a cell culture-adapted virus isolate. A quantitative reverse transcription polymerase chain reaction (qRT-PCR) was developed to examine the virus load in the fish, from which it was found that the highest viral RNA copy number was detected at 5 day post infection (d.p.i), of the 90 day experimental infection period. Characteristic pathological lesions were only seen in the pancreas and the heart but not in the skeletal muscles of the infected fish. A gene expression study using qRT-PCR revealed the rapid induction of interferon (INF) and INF-associated genes in the head kidney of the infected fish compared to the control fish. The Mx protein was found to be highly expressed in the heart and the mucous membranes of infected fish by immunohistochemistry. Interestingly, the pathological changes that were seen occurred some time after the peak expression of genes associated with the INF-1-pathway. When the host-virus interaction of Atlantic salmon infected with SAV was examined using a microarray, a potent first line defence response was observed, together with the signatures of early activation of the adaptive immune response during the initial stages of the infection. Genes associated with transcription, translation and lipid metabolism were significantly differentially expressed in virus infected fish compared to control fish. A large array of antiviral genes was significantly expressed, amongst which were some of the genes also described in mammalian alphavirus infections. Genes associated with apoptosis and anti-apoptosis were also seen to be differentially regulated showing the complexity of the host-virus interaction. Collectively, all of these findings suggest that a non-specific antiviral immune response takes place providing rapid immune protection during the early stages of SAV infection in salmon. In the study on morphogenesis of SAV in salmonid cells using electron microscopy (EM), a rapid internalization of virus into the cells and generation of replication complexes using the secretory pathway of the cell, similar to mammalian alphavirus replication was observed. The mature viruses were released through surface projections, acquiring envelopes from the host cell membrane. From the ultrastructural studies of the salmonid cells infected with SAV, a progressive chromatin marginalisation and condensation could be seen, leading to cellular fragmentation, forming membrane bound apoptotic bodies, characteristic of progressive apoptosis. The activation of caspase-3 in the cytoplasm and genomic DNA damage were also seen in the infected fish cells, indicating that apoptosis is the main cause of cell death during SAV infection. The results of this study have increased our knowledge and understanding of the cellular and molecular mechanisms involved in the pathogenesis of SAV infection, emphasising the importance of the first line defence mechanisms against SAV infection in salmon. This has given an interesting insight into the host mechanisms used to combat the virus during infection, and will undoubtedly be useful for designing new vaccines and management strategies for prevention and control of this important disease

Pre-harvest sexual maturation in farmed Atlantic salmon, Salmo salar, remains a key biological bottleneck compromising biomass and financial output, production predictability, environmental respect, stock welfare and the overall sustainability of the on-growing industry. The management practices currently in place are not optimized and events of high maturation rate are still sporadically observed. From an ecological perspective, the escape of reproductively competent, domesticated Atlantic salmon constitutes a threat to the integrity of wild stocks. The forecasted expansion of the Scottish salmon industry compels the need for a comprehensive and more reliable control of sexual maturation. The general aim of this research project was to optimize the current management strategy (windows of light-manipulation and quality grading) and test alternative practices (lighting-technologies, selective harvest and triploidization) in the control of pre-harvest sexual maturation within the Atlantic salmon on-growing industry. In that end, a number of trials were performed using stock reared in sea-cages on a full commercial-scale or in tanks on an experimental scale. The results of this project are organized around three experimental chapters dealing consecutively with body-size dimorphism, grading and harvest quality; light manipulations and triploidy. In each chapter, two original manuscripts either published or in review are included. In addition to these experimental results, a literature review chapter composed of two review papers on the photoperiodic synchronization and developmental regulation of maturation in salmonids and on morphological skin colour changes in teleosts (published) are presented. In the first experimental chapters, we aimed at investigating the possibility of detecting and selectively harvesting a high proportion of sexually recruited fish before flesh quality deterioration. Results clearly showed that body-size dimorphisms between maturity cohorts at the end of the anabolic window of reproduction (June/July) are strong and standard predictors of maturation among related populations with the same freshwater history. Dimorphism can therefore be modelled to easily and accurately estimate maturation rate in a number of discrete rearing-units. If required, a high proportion of sexually recruited fish can be selectively harvested as superior quality product while leaving the immature fish for further on-growing. This provides an alternative to visual grilse grading that is not feasible in large-scale aquaculture systems, prevents downgrading and increases production predictability as compared to emergency harvests. Furthermore, our results showed immature males grow faster than immature females which should be further investigated to fully determine gender specific performances and nutritional requirements. Weight-grading performed earlier in the cycle affects the sex-ratio within individual pens and in turn apparent performance. This work also revealed that Atlantic salmon can exhibit significant variations in skin colouration resembling the onset of nuptial display but that are not related to sexual recruitment and do not correlate with reduced flesh quality. This originates from a lack of purine (silver) pigments which was also identified, to a larger extent, as characteristic of the nuptial display. This suggests a degree of desmoltification in these histologically immature fish. The instrumental colouration of the altered phenotype was shown to be improved towards a more silver-like appearance by direct ice-contact. This knowledge could facilitate post-harvest quality grading towards the most appropriate market channel and increase product acceptance and attractiveness. The second experimental chapter investigated the possibility of improving photoperiodic manipulation used to suppress early maturation, currently applied for 6-months during the second winter at sea using wide-spectrum, high-intensity lighting systems. Our results showed that the window of continuous artificial-light (LL) exposure can be reduced to 4-months following its onset in early January without compromising its efficiency in suppressing pre-harvest maturation. In addition, alternative lighting technologies were also highly potent at suppressing sexual maturation. The mean-irradiance (intensity) generated within a commercial sea-cage was inversely proportional to the suppression of nocturnal plasma melatonin (light perception hormone) and negatively correlates with the maturation rate within the commercial sea-pen. Threshold levels of light-intensity required to achieve optimal (total) suppression of sexual maturation are suggested. Alternative, narrow band-width lighting-technologies (cold cathode and light-emitting diodes) present an array of technical, practical, economic and welfare benefits comparing to the system currently in use. Clear improvements of the photoperiod-manipulation strategy were demonstrated and these would reduce economic and environmental costs but also potential impacts on animal welfare. The third experimental chapter showed the strong potential of sterile-triploid Atlantic salmon stocks both in freshwater and seawater. Triploid out-of-season smolts were produced for the first time using a classical accelerated "square-wave" photoperiod. Triploidization affected the smoltification pattern but had no detrimental effects on freshwater and early seawater performances under both a S0+ and S1 regime. This illustrates the need to adapt the timing of seawater transfer for successfully producing triploid Atlantic salmon post-smolts. Following one year of seawater rearing, the prevalence of external deformities was higher in triploids but remained within acceptable levels. Importantly, the incidence of vertebral deformities and ocular cataract was higher in triploids possibly due to their specific requirements. It is suggested that tailoring the diet to the nutritional requirements of triploids holds strong potential for remediation. This must be addressed if the use of sterile-triploid stock is to become a commercial reality. The present research project provides means to optimize the maturation management strategy within the Atlantic salmon on-growing industry through light-manipulation, maturation detection and selective harvest, and quality grading. Proposed improvements have the potential to increase biomass and financial output, production predictability, environmental respect and animal welfare and will allow standardization of the overall control of pre-harvest sexual maturation. Their implementation provides a comprehensive strategy likely to favour a sustainable expansion of the Atlantic salmon industry. From a longer term perspective, the rearing of sterile-triploid stocks is promising and should be actively investigated to isolate domesticated strains from their wild conspecifics. This would also eliminate the need for on-growers to deploy a maturation management strategy that that might still affect stock welfare and remains, despite the strong improvements demonstrated, not 100% reliable, costly, technical and protracted.