A NEW METHOD FOR LIVE-STAINING PROTISTS WITH DAPI AND ITS APPLICATIONAS A TRACER OF INGESTION BY WALLEYE POLLOCK (THERAGRA-CHALCOGRAMMA (PALLAS)) LARVAE

The efficacy of DAPI (2,4-diamadino-6-phenylindole), a fluorescent DNA -specific stain, to live-stain protists was evaluated for use as trace rs in laboratory studies of feeding by larval pollock, Theragra chalco gramma (Pallas). At 4 mu g . ml(-1), DAPI effectively live-stained all eight species of heterotrophic protists examined. DAPI also stained f our species of autotrophic protists although staining was more variabl e. No toxic effects of DAPI were detected. DAPI did not appear to alte r the swimming behavior of stained protists. Further, the growth rates of a ciliate, Euplotes sp. and an autotrophic flagellate, Rhodomonas salina (Wislouch) Hill and Wetherbee, exposed to DAPI, did not differ significantly from growth in controls. When DAPI-stained Euplotes sp. were presented to larval pollock, ingested cells were easily seen in l arval guts. This is the first report of ingestion of an aloricate cili ate by larval pollock. The lack of toxicity of DAPI and the easy visua lization of ingested DAP1-stained protists, make this method a useful new tool for examining the ingestion of protists by metazoa and other protists.