Fish diseases and various parameters associated with disease caused mortality of fish were monitored at the Oregon State University Marine Science Center and at a private mariculture facility on Yaquina Bay during a period of five years. Nearly all disease problems observed were caused by Vibrio anguillarum and Vibrio spp. Infection by Vibrio spp. resulted in substantial mortality (as high as 50% of a population) among fish which were immunized against two serotypes of V. anguillarum and among non-immunized fish. Naturally occurring levels of V. anguillarum in Yaquina Bay were determined to be ten or less viable cells per ml water. Effluent water from groups of salmonids with naturally acquired vibriosis contained 1.0 to 4.3 x 10�� viable cells of V. anguillarum per ml. The histopathology associated with naturally acquired and experimentally induced infections of vibriosis in chum salmon fingerlings was described for the two serotypes of V. anguillarum which commonly cause epizootic levels of mortality among salmonids reared at mariculture facilities in the Pacific Northwest United States. Results of these studies indicate that different histopathologic changes are produced by the two serotypes of V. anguillarum. One serotype (referred to as V. anguillarum serotype I) produced a bacteremia in early stages of disease with the following organs and tissues being the main targets: blood, loose connective tissue, kidney, spleen, posterior gastrointestinal tract, and gills. The second serotype (referred to as V. anguillarum serotype II) produced a bacteremia in late stages of disease with the following organs and tissues being main targets: skeletal muscle, cardiac muscle, anterior gastrointestinal tract, posterior gastrointestinal tract, and gills. Vibrio anguillarum serotype I cells were evenly dispersed throughout infected fish tissues while V. anguillarum serotype II formed distinct colonies in tissues of fish. Experimentally induced infections of chum, coho, and chinook salmon were studied to compare the histopathologic changes associated with infections of V. anguillarum serotypes I and II and to obtain. quantitative data concerning some specific effects produced in fish infected with these organisms. Differences in histopathology noted above were observed in all three species of fish when infections of the two serotypes of V. anguillarum were compared. Cellular responses were rarely observed during early or late stages of vibriosis. The data suggest that both serotypes of V. anguillarum used in these studies produce a leukocidin in fish because infected fish had 80% to 95% less leukocytes than non-infected control fish. Extremely high levels of V. anguillarum were shown to be present in fish tissues. Pathology observed in the mucosa of the gastrointenstinal tract of infected fish was apparently related to pH. The anterior gastrointestinal tract was strongly acidic and contained no necrosis of the mucosa while the posterior gastrointestinal tract was not acidic and contained massive necrosis and sloughing of epithelial cells in the mucosa. Experimentally induced infections of vibriosis with water born exposure of fish to live bacteria were used to study the progress of disease. Both serotypes of V. anguillarum used in these studies were shown to enter fish by penetrating the descending intestine and rectum. Penetration of the skin is a second means by which V. anguillarum serotype II enters fish. Moribund fish in all studies suffered from hypoxia, possible accumulation of toxins (although not highly potent), loss of fluids in the posterior gastrointestinal tract, and dysfunction of various organs. Death of fish was apparently due to a combination of these ill effects. / Graduation date: 1979

No description available.

No description available.

With the hope of being able to demonstrate the relative effect of predator species on the young sockeye (Oncorhynchus nerka) in different lakes, the Skeena river investigation instituted a program of standard gill-netting in 1945. Study of the catches and information obtained from netting experiments indicated that the catch per net-night was the best estimation of the concentration of each preying species in different areas. Coupling this catch per net-night with the average volume of sockeye found in the stomachs of predators caught, a measure of predation called the "predation index" was calculated. On the basis of this index, the populations of nine lakes of the Skeena drainage were classified as either high, low or intermediate in effect on young sockeye. / Science, Faculty of / Zoology, Department of / Graduate

Studies of Saprolegnia infections of fish in British Columbia were made to determine disease causing agents and infection conditions. Saprolegnia diclina Humphrey was the most frequently observed parasite. This fungus reproduced sexually both on fish tissue and hemp seed cultures. No definite isolations of S. parasitica Coker were made although some non-sexually reproducing isolates of a Saprolegnia sp. were found. The validity of the species, S. parasitica, has been examined and questioned on the basis of present identification characteristics. Infection studies using S. diclina as the parasite and fingerling coho (Oncorhynchus kisutch) as the host indicated a distinct correlation between temperature and infection. At normal cool temperatures, e.g., 8° C, no infection occurred; at 9°C or above, some infection resulted. Above 9° C, the rate of infection increased as temperature increased. Temperature was also associated with the time at which infection occurred after inoculation. At 18°C, infection began earlier than at 13 C, Heat-shock treatment tended to reduce the temperature-time effect causing initial infection at 13°and at 18° C to occur almost simultaneously. Cold-shock treatment resulted in some infection. Such treatment, however, did not produce the same immediate infection as heat-shock. Histological studies demonstrated the infection to be concentrated in the host epidermis with fungal hyphae at sites of heaviest infection extending through the dermis and into underlying muscle tissues. / Science, Faculty of / Botany, Department of / Graduate

Graduation date: 1991

An oral Vibrio vaccine for salmonids was developed. The vaccine was produced by spray coating lyophilized formalin-killed whole cells of Vibrio anguillarum (VA LS 1- 74) onto non-pareil sugar beads. Then methacrylic acrylic acid copolymer (Eudragit L-30D) was applied as an enteric protective coating. Using x-ray radiographic techniques, it was found that large particles (> 1.1 mm) remain in the fish stomach for more than 2 hours before they would enter the pyloric caeca. The pyloric sphincter which has an opening of 0.94 mm, acts as barrier to prevent the passage of large food particles in the stomach to the pyloric caeca. Based on this information non-pareil sugar beads of 18-20 mesh or smaller should be used as the vaccine carriers. A 15% (w/w) Eudragit L-30D coating is needed to provide enteric protection of the vaccine loaded sugar beads of 18-20 mesh size. Lower levels of coating resulted in the bead breaking down in the stomach and releasing contents prior to entering the pyloric caeca. Since the lymphoid tissues are diffuse throughout the whole GI tract, it may not be necessary to target a vaccine to deliver antigens to a specific area of the intestinal tract, but only protect the antigens from gastric fluids. In vitro dissolution studies indicate that 10% VA LS 1- 74 loading was sufficient for rapid vaccine release (42% released in 30 minutes) and a 15% Eudragit L-30D coating was suitable for providing protection against stomach acid. The vaccine product used in vivo studies contained 10% VA LS 1- 74 and 15% Eudragit L-30D on non-pareil sugar seeds of 18-20 mesh size. Coho salmon were given the vaccine orally, and 30 days afterward a live challenge test was performed. There was no significant difference in the survival rates in a live bacteria challenge test with the positive control (83.3%) and test (80.3%) groups. Both had higher survival rates than the no vaccine fed control group. The serum and mucosal antibody levels to Vibrio were significantly higher (p<0.01) in the test group (19700 units/ml) than the other two groups (2530 units/ml in the positive control group and 617 units/ml in the negative control group). The antibody titer appears to be a better indicator for vaccine efficacy than survival rate of live bacteria challenge tests. The oral Vibrio vaccine developed is effective, and the technique to protect the antigen can be applied to other antigens or proteins for oral delivery producing an economical pathway for mass vaccination of fish. / Graduation date: 1991

Juvenile chinook salmon (Oncorhynchus tshawytscha) were experimentally infected with Renibacterium salmoninarum (Rs), the causative agent of bacterial kidney disease (BKD), to investigate the effects of BKD on three aspects of juvenile salmonid performance: (1) predator avoidance ability; (2) smoltification; and (3) physiological responses to stress. For these experiments, fish with different Rs-infection profiles (created by using an immersion challenge method) were sampled to assess physiological change and subjected to various performance tests during disease progression. When equal numbers of Rs-challenged and unchallenged fish were subjected to predation by northern pikeminnow (Ptychocheilus oregonensis) or smallmouth bass (Micropterus dolomieui), Rs-challenged fish were eaten in significantly greater numbers than controls by nearly two to one. A progressively worsening infection with Rs did not alter the normal changes in gill ATPase and condition factor associated with smoltification in juvenile chinook salmon. A dramatic proliferation of BKD was associated with maximal responses of indicators of smoltification, suggesting that the process of smoltification itself can trigger outbreaks of disease. When Rs-infected fish were subjected to three 60-s bouts of severe handling that were separated by 48-72 h, this experience did not lead to higher infection levels or increased mortality when compared to diseased fish that did not receive the stressors. Furthermore, the kinetics of plasma cortisol, glucose, and lactate over 24-h following each stressor were similar between fish with moderate to high BKD and those that had low or no detectable infection. Fish with moderate to high Rs infections had higher titers of cortisol and lactate prior to each application of the stressor and were also unable to consistently elicit a significant hyperglycemia in response to the stressors when compared to fish with low infection levels. During all experiments, fish consistently developed decreased hematocrits and blood glucose levels and increased levels of cortisol and lactate as the disease worsened, indicating that BKD is stressful, particularly during the later stages. Collectively, these results illustrate the impact of BKD on juvenile salmonids and have also ascribed some ecological significance to this disease beyond that of direct pathogen-related mortality. / Graduation date: 1999

No description available.

Pacific salmon reared commercially off of the Coast of British Columbia suffer great mortality losses to Bacterial Kidney Disease (BKD), caused by the diplobacillus bacterium Renibacterium salmqninarum. This thesis investigates the effects of environmental conditions on the growth performance and disease susceptibility of salmonids reared in captivity. I found that growth rate of chinook salmon was significantly higher in fish fed to 100 compared to 67 % of satiation during the first 175 days of saltwater rearing but not during the first winter. Feed coversion rate was significantly higher for fish fed at 100 % of satiation compared to 67 % of satiation and higher during the winter compared to summer and fall, irrespective of feeding level. Mortality rates were significantly higher during the summer than during the fall or winter, irrespective of experimental treatment. The last BKD sampling period (day 263) revealed that infection rates were directly proportional to stocking densities of 1.5 to 4 kg.m⁻₃. Hatchery-reared chinook salmon held in freshwater aquaria had significantly lower hematocrit and plasma cortisol concentration increases in response to increased stocking density than did their wild counterparts. Crowding of hatchery-reared and wild chinook salmon resulted in equally increased mortality rates for both groups of fish. Day 33 plasma cortisol concentrations in Atlantic salmon held at three stocking densities were directly proportional to stocking densities of 8 to 64 kg.m⁻₃. The ability of anterior kidney lymphocytes from these fish to produce antibody-producing cells was inversely proportional to the density at which the fish were held. / Land and Food Systems, Faculty of / Graduate