- Shortnose Sucker (Chasimistes brevirostris) and Lost River Sucker (Deltistes luxatus) are endemic to the Upper Klamath Basin of Southern Oregon and Northern California. Populations of these fishes have been dwindling since the 1960’s and both species where listed to as endangered in 1988. Poor recruitment is thought to be a major cause of their decline and there is evidence that there hasn’t been strong recruitment since the early 1990’s. In this study, I examined the effects parasites and lesions have on underyearling suckers from Upper Klamath Lake. Following an initial study done by Dr. Michael Kent and Dr. Douglas Markle, Oregon State University, in 2013, I conducted histopathological and wet mount examinations on 390 suckers caught during the summers of 2015 and 2016. I also examined an additional 1,355 juvenile suckers that came from 1991-2013 collection from Upper Klamath Lake for the presence of three common parasites, Contracaecum sp. in the heart, and surface infections by Lernaea sp. and black spot metacercariae. From the 1,745 suckers that I examined, I concluded that the most prevalent parasite infections were the copepod Lernaea sp. and skin and muscle metacercariae, both of which caused prominent lesions characterized by replacement of the somatic muscle and severe, chronic inflammation. The most severe lesions were caused by a Contracaecum sp. infection of the heart, which was associated with massive dilation of the atrium an enlargement of the heart overall. However, the prevalence of the infection was low in suckers, and never exceeded 7 %. My study also included wet mount examination of three cyprinid fishes from the lake including Tui Chubs (Gila bicolor), Blue Chubs (Gila coerulea) and Fathead Minnows (Pimephales promelas), all of which are suitable hosts for heart infections by Contracaecum sp. larvae. I extracted DNA from L3 larvae from all three cyprinids plus the suckers, and sequenced the ITS-1 region of the rRNA gene array, Sequences were essentially identical to each other and were most closely related to Contracaecum multipapillatum. To elucidate the life cycle of this Contracaecum sp, I necropsied an American white pelican and found adult worms in the proventriculus that matched the IT-1 gene sequenced from L3 larvae found in the fishes. I also attempted to elucidate the life cycle of the trematodes infecting the suckers in the lake. I examined 21 species of cercariae from 8 different species of snails. Ten of these cercariae species were known to infect fish, but none of the sequenced cercariae were a match to the 28s rDNA sequenced from metacercariae found from fishes in Klamath Lake. This demonstrates the specious nature of Digenae in the lake.
Three myxozoans were observed in the histological samples of the suckers; a Parvicapsula sp. in the renal tubules, a Myxobolus sp. in the intestinal mucosa, and an unusual multicellular, presporogonic myxozoan in the intestinal lumen of one Lost River Sucker. I also observed two undescribed species of myxozoans from Fathead Minnow, a Myxobolus sp. encysted in gills and a Unicauda sp. in the major blood vessels of the kidneys. None of the species of myxozoans from suckers or Fathead Minnows was associated with any significant pathological changes.
I evaluated my data using several accepted methods used by parasitologists to determine parasite associated mortality, including determining the frequency of lethal infections, comparison of the observed frequency of two independent dual infections with the predicted probability of their occurrence, and the comparison of the observed frequency of parasites with a projected frequency based on lightly infected individuals, also know as the Crofton analysis. I found no direct quantitative link of the parasites to mortality using these methods. Two useful methods, observing a decrease in the prevalence of long-lived parasites over time and observing a decrease in the variance/mean ratio for the parasites with host age, require the ability to examine hosts of a given population at later time points, which in my case would require examination of yearling fish. These analyses could not be performed because suckers of this age are rare in the lake. Nevertheless, given the degree of lesions and prevalence of the Lernaea sp. and the black spot metacercariae, these should still be considered as contributing causes of reduced survival past the underyearling stage.