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Parasite prevalence and composition in Tui Chub in Eastern California freshwater ecosystems


Parasites and pathogens exert strong selection on their hosts and alter the structure, diversity, and productivity of communities of ecosystems. This paper presents results of a survey of parasite composition and prevalence observed on and within the freshwater hybrids Owens (Siphateles bicolor snyderi) and Lahontan (Siphateles bicolor obesa) Tui Chubs, a native minnow species, in the Eastern Sierra Nevada mountains of California. The Owen and Lahontan Tui Chub is present in many lakes and rivers in Northern California and its parasite community has yet to be characterized. My thesis asks what kinds of parasites are found in the freshwater Tui Chub, which lakes or streams held the highest parasitic loads, and which features of individual fish and the habitat influence parasite density and/or types of parasites. Fish samples were collected in Summer 2019 by PhD student Henry Baker at 10 different sampling sites including freshwater lakes and streams that vary in size, temperature, water chemistry and species present across Owens Valley, California. I dissected 134 individual fish to characterize the ecto- and endo-parasite communities. My results show that two of the locations had significantly higher parasite infection rates than the others, where few macroscopic parasites were observed. These two locations were both geothermal with warmer waters and distinct water chemistry with high salinity and alkalinity. This pattern suggests that some aspects of geothermal habitat favor the parasite life cycle and makes fish in these sites more easily accessible as a host, though the mechanism behind the pattern is unknown. Four main types of visually distinct parasites were found: one adult life-stage tapeworm, one adult life- stage nematode and two metacercaria trematodes, though none were identified taxonomically. The greater parasite infection rates in geothermal habitats may be related to the greater abundance of snails in these sites, which may serve as intermediate hosts to fish parasites. No differences in parasite infection rates or composition were observed between lake and stream habitats. My thesis suggests that the atypical thermal and chemical environment of geothermal springs promotes parasitism in Tui Chub, but that lakes and streams are similar in containing low rates of infection by any parasites among fish.

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