Simultanous measurements of bacterial production (3~-thymidine incorporation) and ciliate bacterivory (uptake of fluorescently labeled bacteria, FLB) were carried out on samples from the epilimnion of 17 lakes in eastern Norway. On average, bacteria equivalent to 19% (range: 0.8 to 62%) of the bacterial production were consumed by ciliates. The most important bacterivorous ciliates were small (c30 pm) oligotrichs; Halteria grandinella and Strobilidium spp. These ciliate taxa were found to have average clearance rates of 183 and 103 nl cell-' h-' respectively, corresponding to specific clearance rates of 0.5 and 0.9 X 10' cell volumes h-' In addition, Vorticella sp., a peritrich ciliate that was attached to colonies of the cyanophyte Anabaena flos-aquae, was found to be important in several lakes. On average, these 3 ciliate taxa alone accounted for >80% of total ciliate bacterivory. Speciesspecific clearance rates did not vary much between lakes, indicating that the ciliates were always food limited. These results confirm other recent studies, showing that pelagic ciliates can be significant grazers on bacterioplankton.

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