VIABILITY OF NOTOCOTYLUS-ATTENUATUS (TREMATODA, NOTOCOTYLIDAE) METACERCARIAE UNDER ADVERSE CONDITIONS

The viability of Notocotylus attenuatus metacercariae was 80% at 20 wk post-encystment (PE) and decreased to 10% at 24 wk PE. Cyst viability was influenced by the duration of cercarial swimming activity prior t o encystment, by the occurrence of cyst associations, and by the type of cyst storage. This is the first report on cyst associations formed by Notocotylidae cercariae. Cyst associations were formed only by cerc ariae encysting shortly after their emergence from snails. In cyst ass ociations metacercariae did not overlap, but were separated by regular distances ranged from 20.4 to 24.5 mu m ($) over bar x = 22.3 mu m, S E= 0.41 The mucoid materials which formed the external cyst wall cover ed the areas between parasites seven if distances were comparable with the cyst size. In cyst associations, metacercariae in the water and t hose located close to the water were viable up to 24 wk PE. Cercariae with extended swimming activity did not form associations even when pr esent in numbers, less than or equal to 50 cercariae per cm(3). The cy sts established by these cercariae had a thin external cyst wall, and were not viable by 12 wk PE.