Markle et al.  2020. Intl. J. Parasitology – In Press.

The survival of two fish species, the  Shortnose Sucker and Lost River Sucker, is seriously threatened in the Upper Klamath Lake. This watershed is extremely complicated; it was dramatically altered over 100 years ago for agriculture needs, and is very shallow, hyper-eutrophic and does not meet certain Clean Water Act criteria.  These fishes are long-lived fishes, spawn every year, but in spite of this no young fish are surviving past 1 year of age.

For over 25 years Dr. Doug Markle, Department of Fisheries and Wildlife has been studying the biology and causes of decline in these fishes.  Dr. Michael Kent, Microbiology and his students joined the Markle team about 5 years ago to investigate diseases and parasites in these fishes, and we have identified three common parasites that are highly pathogenic to the suckers (Janik et al. 2018).  They are a larval trematode (Bolboporus sp.), a larval nematode (Contracaecum sp.), and a parasitic copepod Lernaea cyprincacae.  Restoration of the marsh habitat in the lake was conducted to improve young fish survival.  The environment is complex, and sometimes good intentioned changes to the environment cause unforeseen, negative consequences.  As documented in other watersheds, restoration of marsh areas is usually good for the ecosystem, but restoration may enhance parasites that use snail intermediate hosts, such as the trematode, Bolbophorus sp.  Adding to the success of the parasite life cycles, the lake has an abundant pelican population, and both the trematode and the Contracaecum sp. nematode use pelicans to complete their life cycles.

Recently, we analyzed parasite burdens on some 20,000 underyearling suckers collected over 25 years (Markle et al. 2020).  Some findings of these analyses were that certain parasites increased following a major marsh restoration project and that patterns of infections by the parasites indicated that they were associated with host mortality.  Lernaea cyprinacae is an exotic invader, and has been introduced to various lakes around the world.  It was likely introduced to the Upper Klamath Lake in the 1970s but was absent on juvenile suckers in the early 1990s when there was good year-class production of the suckers.

Markle et al.  2020. Intl. J. Parasitology – In Press.  Title: Odds ratios and hurdle models: a long-term analysis of parasite infection patterns in endangered young-of-the-year suckers from Upper Klamath Lake, Oregon, USA

Abstract: We used odds ratios and a hurdle model to analyze parasite co-infections over 25 years on >20,000 young-of-the year of endangered Shortnose and Lost River Suckers. Host ecologies differed as did parasite infections. Shortnose Suckers were more likely to be caught inshore and 3 – 5 times more likely to have Bolbophorus spp. and Contracaecum sp. infections, and Lost River Suckers were more likely to be caught offshore and approximately three times more likely to have Lernaea cyprinacea infections. An observed peak shift seems likely to be due to a lower host size limit for Bolbophorus spp. (13.6 mm) compared with L. cyprinacea (23.4 mm).  The large data set allowed us to generate strong hypotheses: i) that a major marsh restoration project had unintended consequences that resulted in an increase in infections; ii) that co-infection with Bolbophorus spp. increased the odds of infection by L. cyprinacea and Contracaecum sp.; iii) that significant declines in the odds of infection over approximately 25 days were due to parasite-induced host mortality; iv) that the fish’s small size relative to L. cyprinacea and Contracaecum sp. might be directly lethal; v) that the absence of L. cyprinacea infections in the early 1990s was associated with good year-class production of the suckers; and vi) that parasites might increase the odds of vagrancy from the nursery ground.