Theses and Dissertations at Montana State University (MSU)
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Item Factors affecting the resistance of juvenile rainbow trout to whirling disease(Montana State University - Bozeman, College of Letters & Science, 2003) Ryce, Eileen Karpoff NicolItem Influence of environmental features on Tubifex tubifex and Myxobolus cerebralis infected Tubifex tubifex in Yellowstone National Park : implications for whirling disease risk(Montana State University - Bozeman, College of Letters & Science, 2010) Alexander, Julie Diane; Chairperson, Graduate Committee: Billie L. KeransWhirling disease (WD) is an emerging parasitic disease of salmonids that is increasing in severity and geographic range. Whirling disease is caused by the myxosporean parasite, Myxobolus cerebralis, and can effect significant mortality in wild and cultured salmonid populations. Myxobolus cerebralis was recently detected in Yellowstone National Park (YNP) where it may be causing native Yellowstone cutthroat trout (YCT) to decline. Myxobolus cerebralis exploits the aquatic oligochaete, Tubifex tubifex, as its primary host and spores released by T. tubifex are infective to salmonid fish. The aim of this study was to assess WD risk for YCT populations in YNP by focusing on the disease source, T. tubifex, which had not previously been characterized. My objectives were to characterize T. tubifex populations and dynamics of M. cerebralis infections in T. tubifex and to establish factors associated with M. cerebralis infections in T. tubifex. In addition, I examined relationships between infection dynamics in T. tubifex and transmission to fish hosts (WD risk). In Pelican Creek, T. tubifex and M. cerebralis infected T. tubifex were widely distributed and abundant. Infected T. tubifex were most abundant in reaches characterized by intermediate geothermal influence. However, WD risk was high in all reach types, which indicated that low parasite success in the oligochaete host in reaches with high or no geothermal influence did not translate into reduced WD risk in these reaches. In tributaries throughout YNP, susceptible T. tubifex were widely distributed but experimental and field data suggest M. cerebralis-infected T. tubifex may be unable to survive in all tributaries where uninfected T. tubifex were found. In particular, environmental factors influenced by confinement, including proportions of coarse and fine substrates, may preclude establishment of M. cerebralis in tributaries in YNP. Thus, environmental features, rather than oligochaete host factors, may be most influential for M. cerebralis dynamics in T. tubifex and WD risk to fish in YNP. While further research is needed to identify specific mechanisms, these results suggest environmental features related to confinement may be useful for assessing WD risk at broad scales when the oligochaete host is characterized by low genetic variability.Item Myxobolus cerebralis in native Cutthroat trout of three spawning tributaries to Yellowstone Lake : a qualitative ecological risk assessment(Montana State University - Bozeman, College of Letters & Science, 2008) Murcia, Silvia; Chairperson, Graduate Committee: Billie L. Kerans; Todd M. Koel (co-chair)Most environments impose periodic or stochastic stress on natural populations, which increase susceptibility to diseases. Infection by Myxobolus cerebralis (exotic parasite causing salmonid whirling disease) is strongly influenced by a stream's physicochemical attributes and stressors, which may also affect host pathology. Susceptibility to M. cerebralis varies greatly among different species and subspecies of the salmonid host, but little is known about lesion severity or location of infection among the native Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri). In 2002 and 2003 we performed a series of 10-day sentinel cutthroat fry exposures and habitat assessments in various sites of three M. cerebralis-positive tributaries to Yellowstone Lake: the Yellowstone River, Pelican Creek, and Clear Creek. At 90 and 150 days post-exposure, fry were examined by polymerase chain reaction and histology to determine prevalence, severity, and location of infection. The goal was to identify spatiotemporal patterns of infection, and physicochemical features of the streams influencing it, and potentially facilitating parasite invasion and establishment. Results on fish (young and adult) host infection data, environmental attributes, and tubificid host presence/absence data in the study streams were used to develop an ecological risk assessment for parasite establishment and whirling disease in this ecosystem. Results from our qualitative risk ranking systems suggest that the cutthroat trout of the Yellowstone Lake basin are highly susceptible to M. cerebralis infection, with the most severe lesions in cartilage of the cranium and jaws, especially in systems with high water temperatures and ionic content. Our results also suggest that such environmental features are most conducive to parasite establishment, especially in tributaries of the lake basin used by cutthroat trout as spawning and rearing habitats. Thus, this study has implications for both ecology and parasitology as it reveals that environmental components can affect when and where a pathogen resides within the host, and thereby affect manifestation of disease. Recognition of the specific environmental attributes most conducive to parasite establishment, and disease, can increase future diagnostics, detection, and management efforts, strengthening the likelihood of correctly predicting M. cerebralis' and similar pathogenic invasions and establishment in unsampled sites.Item Identification of life history variation in salmonids using otolith microchemistry and scale patterns : Implictions for illegal introductions and for whirling disease in Missouri River Rainbow trout(Montana State University - Bozeman, College of Letters & Science, 2004) Munro, Andrew Roy; Chairperson, Graduate Committee: Thomas E. McMahon; Alexander V. Zale (co-chair)Proper conservation and management of wild salmonid populations requires correct identification of the array of life histories present and their contribution to adult recruitment. I used otolith microchemistry to identify natal origin and scale patterns to determine outmigration age in Missouri River rainbow trout where whirling disease could potentially cause a population collapse. First, I reviewed the otolith microchemistry literature and concluded that there have been a limited number of freshwater studies, and there has been limited rigorous testing of the many instruments used. Second, I tested the efficacy of time-of-flight secondary ion mass spectrometry (ToF-SIMS) and found that Sr:Ca could be precisely measured in an otolith 'standard', there is a strong relation between qualitative ToF-SIMS results and concentrations measured with an electron microprobe, and the ambient water strongly influences otolith composition. Third, I analyzed the chemical composition of lake trout otoliths to identify the likely source of illegally transplanted lake trout in Yellowstone Lake. Changes in otolith microchemistry of suspected transplants accurately (>90%) determined the likely source of the introduction, and transect analyses indicated that lake trout have possibly been in Yellowstone Lake since as early as the mid-1980s. Finally, I used otolith microchemistry to identify natal origin and scale patterns to identify outmigration age in Missouri River rainbow trout. Otolith microchemistry was not an effective technique for this particular system because of similarities between the two major rainbow trout producing tributaries. However, I demonstrated a technique that uses the relation between otolith and water Sr:Ca to estimate sample sizes required to detect differences between streams. This can be used in future studies as a preliminary test to determine if otolith microchemistry is feasible. Scale patterns revealed that the yearling outmigration life history contributed most (88%) to adult recruitment in the mainstem fishery and the proportion of young-of-the-year to yearling outmigrants did not change post-whirling disease. Rainbow trout in the Missouri River have two obstacles to overcome: 1) severe whirling disease infection if the natal stream has Myxobolus cerebralis; and 2) low probability of surival if they manage to avoid severe infection but leave the stream too early.