Thesis (M. Sc.)--York University, 1997. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 295-307). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL:http://wwwlib.umi.com/cr/yorku/fullcit?pMQ27344.

Some of the most devastating plant and animal pathogens belong to the oomycetes. Saprolegnia parasitica, a major pathogen of freshwater fish and the causal agent of Saprolegniosis, causes large economic losses in aquaculture due to the death of freshwater fish which contract Saprolegniosis. Losses due to Saprolegniosis are also incurred by natural fish populations. Saprolegniosis was previously controlled through the use of a biocide called malachite green, until the dye was found to have potentially carcinogenic effects. Following this discovery, the use of malachite green on fish destined to enter the food chain was banned worldwide and subsequently there has been an increase in the occurrence of Saprolegniosis. This work investigates various aspects of S. parasitica with the view to inform the development of new control strategies. Three cDNA libraries, including two interactive libraries, were analysed and bioinformatics provided valuable insight into the genes expressed not only by S. parasitica but also by the host. The annotation and expression profiles of several of these genes are described in this work and the potential of S. parasitica genes as vaccine targets is discussed. One protein, identified as a vaccine candidate, is annotated, cloned and overexpressed in order to evaluate its efficacy as a vaccine. It has been shown previously that the plant pathogenic oomycete Phytophthora infestans is able to utilise a protein localisation motif, the RxLR, in order to translocate effector proteins into the host. The question as to whether S. parasitica possesses a similar translocation system is addressed in this work. Localisation studies on an RxLR protein of S. parasitica origin are described and the microscopic interaction between S. parasitica and its host are described and attempts to optimise production of interaction structures are discussed.

No description available.

No description available.

An understanding of the level of both genetic and morphological diversity within a taxon and how that diversity is structured within and across habitats is important when determining the conservation value of that taxon and for successful habitat management programs to be developed. Atlin Lake is a large lake in northern British Columbia and is one of the largest lakes that contain relatively unperturbed populations of lake trout (Salvelinus namaycush). As the top aquatic predator, lake trout in Atlin Lake are a key component of the lake’s fish community and are important for local fisheries. I assayed lake trout from Atlin Lake and other western lake trout populations at eight microsatellite DNA loci and for body morphology to determine: (i) the level of genetic variation present, (ii) the level of substructure that occurs in Atlin Lake, and (iii) whether there was a relationship between the genetic and morphological variation present. STRUCTURE analysis identified five subpopulations within Atlin Lake. Morphological analysis was used to differentiate between the samples collected throughout Atlin Lake. Cluster analysis of size corrected data separated the fish into two groups making Atlin Lake the smallest lake identified to date to possess more than one morphotype. Genetic and morphological groupings were found not to be correlated with each other. Finally, I was interested in whether each of the genetic subpopulations contributed equally to the local fisheries catches. A mixed stock analysis of samples collected from the commercial fishery and recreational anglers indicated that all of the genetic subpopulations contribute to the fishery along with lake trout subpopulations in the interconnecting Tagish Lake; suggesting that no one subpopulation is being depleted by the fisheries. Continued genetic monitoring, however, is necessary to see if the trends in fishery contribution are temporally stable. Future studies should focus on understanding the source of the morphological variation and maintenance of genetic substructure.

No description available.

The significance of <i>Diptostomum spathaceum</i> to trout farming was highlighted in a nationwide survey and the importance of the snail intermediate host <i>Lymnaea peregra</i> was emphasised by the fact that fish kept in earth units, in which snails were more prevalent, were more susceptible to infection. Studies revealed that <i>Diplostomum</i> spp. metacercariae, present in both the lenses and humours of eyes, were abundant in September. Differences in metacercarial numbers between fry and juvenile fish, and between years, were attributed to the absence of snails within the fry units and differences in snail numbers respectively. Molluscicides were ineffective in eradicating snails but clearing vegetation from units reduced numbers of snails and infection levels dramatically. Diplostomiasis appeared to be more prevalent in areas of a farm where water flow was reduced and where snails were abundant. Comparison of the internal defence system of two populations of <i>L. stagnalis</i> indicated that in both, haemocyte numbers increased and the relative proportions of haemocyte types changed with snail age. Haemocyte phagocytic activity also increased with snail age. However, one population comprised mainly Type I snails (Haemolymph agglutinates erythrocytes at high titres) whilst the other comprised mainly Type II snails (low agglutinin titres). Haemolymph from Type I and II juveniles had comparable agglutinating activities but as snails grew, activity increased in Type I snails whilst that in Type II snails remained low. Plasma from Type I and II snails increased the phagocytic activity, Type I plasma having a more pronounced effect. During the course of the infection with <i>D. spathaceum</i>, both haemocyte- and plasma-associated activity decreased in Type I and II snails. Most markedly, 24 h post-infection (p.i.) phagocytic activity was suppressed and plasma taken from snails 24 h p.i. had a suppressing effect on haemocytes from uninfected adults. An <i>in vitro</i> bacterial killing assay demonstrated that <i>L. stagnalis</i> haemocytes recognize and effectively kill the bacterium <i>Aeromonas salmonicida</i>. Cytochalasin B decreased bactericidal activity implicating both intracellular and extracellular cytotoxicity of haemocytes.

No description available.

Investigations into perispawning mortalities in the brown trout (Salmo trutta L) population of Loch Leven, Kinross, revealed that death occurred as a result of infection with a particular species of Saprolegnia diclina Humphrey type 1. Increased surface area of infection was correlated with a decrease in ion and protein content of the blood and was further reflected by changes in the electrocardiogram pattern. These changes were essentially a widening of the QRS complex with inflection of the RS component, changes consistent with a decrease in certain ions in mammals. Histological changes associated with sexual maturity and fungal infection are described and compared with changes resulting from the administration of androgens to brown trout.

Flavobacterium psychrophilum is the causative agent of rainbow trout fry syndrome (RTFS) and bacterial cold water disease (BCWD) in salmonid fish world-wide. Basic information relating to the antigenic and biochemical characteristics, and pathogenicity of the bacterium are lacking in the literature. Therefore, the aim of this study was to characterise F. psychrophilum based on phenotypic and serological differences between isolates. The bacterium was also characterised by means of its extracellular products (ECPs). An attempt was made to develop an experimental challenge model for the bacterium. Phenotyping of the bacterium was based on growth and biochemical characteristics from which it was found that isolates of F. psychrophilum appeared homogenous. Intramuscular (IM) challenge was the most effective route for experimentally challenging rainbow trout fry with F. psychrophilum. Virulence of the bacterium was determined by injecting rainbow fry IM with different isolates of F. psychrophilum. Variations were found in the virulence of the different F. psychrophilum isolates when injected into fish by this route. The levels of protease activity and auto-agglutination characteristics appeared to vary between the virulent and non-virulent isolates. Electrophoretic analysis of whole cell preparations of F. psychrophilum showed that the protein and carbohydrate banding patterns of the different isolates were similar regardless of their origin or their virulence to rainbow trout. A substantial amount of carbohydrate was associated with the bacterium. Using a commercial glycoprotein detection kit, two glycoprotein bands were found at 20 and 23 kDa in whole cell preparations of the bacterium. The electrophoretic protein profiles of the outer membrane protein (OMP) preparations of the bacteria were similar between both virulent and non-virulent isolates. Characterisation of different F. psychrophilum isolates by an enzyme linked immunosorbent assay (ELlS A) using rabbit antisera raised against a virulent and nonvirulent isolate of F. psychrophilum, showed that there may be between three and five different serological groups. No association was detected between serotypes and geographical origin of the strains, the species of host fish from which they were recovered or the virulence of the isolates. The antisera detected common protein and carbohydrate antigens between the isolates with Western blot analysis. Antigenic differences were found between different F. psychrophilum isolates with ELISA and indirect fluorescent antibody technique (IF AT) using monoclonal antibodies (MAbs) developed against the virulent and the non-virulent F. psychrophilum isolates. Two MAbs (9H9 and 5A9) cross-reacted with a related species of bacterium F. branchiophilum, in the ELISA. Two MAbs (lE5 and 1 lB2) recognised high molecular weight material in whole cell preparations of the virulent F. psychrophilum in Western blot analysis, which also reacted with rainbow trout anti-F. psychrophilum sera raised against the virulent isolate of the bacterium. Due to their lack of specificity or sensitivity, both the rabbit sera and the eight MAbs produced in this study were considered unsuitable as diagnostic probes for screening infected RTFS samples. F. psychrophilum isolates produced varying amount of ECP proteins after 14 days culture in modified Anacker and Ordal's broth (MAOB), which exhibited substantial protease activity for casein and gelatin. However, the ECPs showed only partial haemolytic activity against rainbow trout eryhrocytes. Electrophoretic protein and Western blot profies were found to be very similar between the ECPs of different isolates. The ECP preparations contain glycoprotein molecules of either 20 or 23 kDa. None of the preparations from the virulent and the non-virulent isolates were found to be toxic to rainbow trout fry. The study suggests that isolates of F. psychrophilum are homogeneous in terms of their biochemical and electrophoretic characteristics, while antigenic characteristics varied between the isolates. The bacterium possesses a substantial amounts of carbohydrate and glycoprotein in its cellular and extracellular products.