Rumen fungus Piromyces sp. AO 12 was grown with 14C-oleic acid to yield radio-labelled zoospores. By incubating the labelled zoospores with mixed rumen protozoa, predatory activity of protozoa on fungal zoospores was estimated. The radioactive carbon was incorporated into total fungal cells at an efficiency of 9.5%, 9.8% of which was distributed in the zoospores. A labelled single zoospore was calculated to record 0.080cpm. When the labelled zoospores were incubated with mixed protozoal suspension (1:30 in cell number ratio), significant radioactivity was transferred to the protozoal cells after 1-3 hour, but little with 0 hour incubation. This demonstrates that fungal zoospores are associated with protozoal cells, or possibly ingested by protozoa. A frequency of this association was calculated to be a single zoospore/52 cells of protozoa/hour.
