Graduate Thesis Or Dissertation
 

Impacts of multispecies parasitism on coho salmon (Oncorhynchus kisutch) in Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/w3763965v

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  • Diseases caused by parasites are recognized as significant sources of mortality in wild fish populations. I assessed the impacts of multispecies parasitism on a threatened stock of juvenile coho salmon (Oncorhynchus kisutch). A crucial prerequisite to this research was proper identification of parasites, which can be difficult for species lacking distinct morphological features. Such was the case when I attempted to identify larval Apophallus sp. (Digenea) and a myxozoan infecting peripheral nerves, which I described as Myxobolus fryeri. The second essential step was to document the geographic distribution of infections in Oregon coastal juvenile coho salmon. I found 21 different parasite species in underyearlings and smolts from 10 different rivers. Some parasites, such as Apophallus sp., were more common in underyearlings than smolts and had a more restricted geographic distribution. Additionally, I empirically compared histology to the evaluation of wet preparations for parasite detection. The latter was more sensitive, but the former provided data on tissue level impacts. I then focused my research on parasitized coho salmon from one river, the West Fork Smith River (WFSR). The lower abundance of some parasites in smolts, compared to underyearlings suggested parasite associated mortality. Therefore, I evaluated the persistence of these parasites, as this trend could also be explained by infection recovery. The parasites in my study persisted throughout the overwintering period of these coho salmon. I also conducted a field study involving both pseudolongitudinal and retrospective approaches. Results indicated that up to 95% of parr from the lower mainstem of the WFSR had infections levels of Apophallus sp. that were associated with mortality. I also performed a laboratory study on wild fish from two consecutive year classes and fish experimentally infected with Nanophyetus salmincola. Parasite associations were evaluated for the following fish performances: size, growth, swimming stamina, and gill Na⁺,K⁺-ATPase activity. Parasites were most negatively associated with size and growth, which was remarkably consistent between study years and likely influenced swimming stamina and ATPase activity levels. Taken together, results from the population, individual, and tissue levels, all indicate that these parasites impact this threatened stock of juvenile coho salmon. These results may have implications for fishery management, as it represents a previously unrecognized limiting factor for this recovering population.
  • Keywords: Multispecies parasitism, Histopathology, Land use impacts, Threatened populations, Macroparasite distribution, Disease ecology
  • Keywords: Multispecies parasitism, Histopathology, Land use impacts, Threatened populations, Macroparasite distribution, Disease ecology
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