Spatial and Temporal Occurrence of the Salmonid Parasite Ceratomyxa shasta in the Oregon–California Klamath River Basin

Abstract

The parasite Ceratomyxa shasta has been implicated as a significant source of salmonid mortality in the lower Klamath River, California (i.e., below Iron Gate dam). A study of the prevalence of C. shasta and its geographic and temporal distribution throughout the Klamath River basin was conducted to determine when and where juvenile salmonids encounter lethal parasite doses. Susceptible rainbow trout Oncorhynchus mykiss were exposed to C. shasta 3–4 d at seven locations in the Klamath River between Beaver Creek and Keno Reservoir in April, June, July, September, and November 2003. Individuals from a Klamath River strain of fall Chinook salmon O. tshawytscha were held in three locations in the upper Klamath River in April, June, and July. In June 2004, rainbow trout were exposed to the parasite for 4 d at 18 locations from Klamath Lake to the mouth of the Klamath River, including several major spawning tributaries; one exposure occurred in the lower Klamath River. Rainbow trout mortality due to infection for groups exposed in the upper Klamath River was lower (<8.0%) and delayed (mean time to death, 40–110 d) in comparison with that in groups exposed in the lower Klamath River (>98%; mean time to death, 33–36 d). Experimental fall Chinook salmon did not become infected in the upper Klamath River, but infection was detected in Chinook salmon exposed in the lower Klamath River, nearly 50% of these succumbing to infection. These dramatic differences in mortality between the upper and lower Klamath River could not be explained by differences in water temperatures during exposure and are probably a result of differences in infectious dose. Lack of infection in groups exposed in tributaries supports the hypothesis that the parasite life cycle and the invertebrate host are largely confined to the main‐stem Klamath River.

Distribution and abundance of the salmonid parasite Parvicapsula minibicornis (Myxozoa) in the Klamath River basin (Oregon-California, USA)

“…1) (Stocking et al 2006). Seventy fish were exposed at each location and monitored for 100 d post-exposure as described in Stocking et al (2006). As a negative control, 70 fish were held on a specific pathogen-free water supply and sampled concurrently.…”

“…Dis Aquat Org 78: [137][138][139][140][141][142][143][144][145][146] 2007 the estuary, but absent in tributaries with the exception of the headwaters to Klamath Lake in the upper basin (Hendrickson et al 1989, Stocking et al 2006. Recent studies have also mapped the distribution of the invertebrate host, Manayunkia speciosa, in the river (Stocking & Bartholomew 2007).…”

“…More recently, the parasite was identified in juvenile salmon from the Klamath River (KR), California, USA (Foott et al 2004. The presence and distribution of C. shasta has been well documented in each of these systems (Ching & Munday 1984, Bartholomew et al 1989, Hoffmaster et al 1988, Hendrickson et al 1989, Stocking et al 2006.…”

“…This is in contrast to what is known of the effects of P. minibicornis further north in the Fraser River, British Columbia, where certain stocks of sockeye salmon Oncorhynchus nerka have suffered significant prespawn mortality associated with the infection (St. Hilaire et al 2002, Jones et al 2003. In these fish, severity of infection was affected by migration time and water temperature, with early migrating fish having higher vulnerability to infection as a result of longer holding times in the river before spawning.Reexamination of samples collected during recent studies on the distribution and prevalence of Ceratomyxa shasta in the Klamath system (Stocking et al 2006) allowed us to address these data gaps and to determine the presence and relative abundance of Parvicapsula minibicornis throughout much of the KR basin. Additionally, samples from out-migrating juvenile and returning adult salmon provided an indication of the parasite's biological effects on KR salmon and steelhead Oncorhynchus mykiss.…”

“…During June 2004, sentinel rainbow trout Oncorhynchus mykiss (Roaring River Hatchery, OR), were held for 4 d in cages at 18 locations throughout the KR to monitor for Ceratomyxa shasta presence ( Fig. 1) (Stocking et al 2006). Seventy fish were exposed at each location and monitored for 100 d post-exposure as described in Stocking et al (2006).…”