ABSTRACT: Sporonts of the paramyxean protist Marteilia sydneyi, aetiological agent of 'QX' disease in the Sydney rock oyster Saccostrea commercialis, were isolated from infected oysters and maintained under various physical conditions to assess their survival. Survival was determined using 2 fluorogenic dyes, propidium iodide and 4',6-diamidino-2-phenylindole. The effects of salinity, temperature, ingestion by natural oyster predators, freezing and chlorination were examined. Dye exclusion indicated that spores were short-lived once isolated from the oyster, with the majority dead within 7 to 9 d. Maximum longevity recorded was 35 d at 15°C and 34 ppt. Experiments to investigate the effects of ingestion by fish and birds revealed that spores did not survive for more than 2 h under these conditions, suggesting that it is unlikely that fish or birds play a significant role in the life cycle or dispersal of this parasite. Spores apparently remained viable for over 7 mo when frozen at -20 and -70°C. Chlorine treatments of 200 ppm killed 99.5% of spores within 2 h and all spores within 4 h of exposure.

KEY WORDS: Viability · Marteilia sydneyi · Propidium iodide · 4',6-diamidino-2-phenylindole · QX · Saccostrea commercialis · Fluorogenic dyes

Published in DAO Vol. 36, No. 3 (1999) on May 31
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1999