Infestation of a peritrich ciliate (Epistylis lacustris) on a calanoid copepod (Leptodiaptomus minutus) in a small, oligotrophic, northern temperate lake (Crystal Lake)
Specimens of the calanoid copepod Leptodiaptomus minutus collected in June 1994 in an oligotrophic northern temperate lake, Crystal Lake, were commonly infested with the stalked ciliate Epistylis lacustris. E. lacustris appears to be highly specific for L. minutus and no other coexisting zooplankters were infected. Field cubitaner experiment was conducted to examine the influence of copepod density on the infection of the ciliate. A higher copepod density in the cubitaner resulted in a significantly higher infection rate. but the ciliate load did not differ significantly among the treatments. Except for nauplii nearly 70\% copepods carried l-20 ciliates, although the maximum load was as high as 250 ciliates. However. both infection rate and ciliate load of nauplii were much lower than those of other copepod stages. The infection of the ciliate had no significant influence on the average egg number of the copepod.
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