Occurrence of thraustochytrid fungi in corals, fresh coral mucus and floating and attached mucus detritus from the Lakshadweep Islands in the Arabian Sea was studied. Corallochytrium limacisporum Raghukumar, Thraustochytrium motivum Goldstein, Labyrinthuloides minuta (Watson and Raper) Perkins, L. yorkensis Perkins and Ulkenia visurgensis (Ulken) Gaertner were isolated. C. limacisporum was the most common and was detected in the polyps of 3 corals using immunofluorescence. Mucus detritus from Kalpeni Island harboured 1.9 x 10 super(6) thraustochytrids.g/1 dry weight and fresh mucus from Acropora sp. 12 and 20.ml/1. The number of thraustochytrids in detrital mucus incubated with sterilised lagoon water increased significantly than when incubated with unsterilised water, suggesting grazing by protozoans. Fresh mucus may be further colonisEd. by thraustochytrids once liberated into the water. Ciliates could be maintained in the laboratory on cells of C. limacisporum