Abstract: 　Objective To investigate the ecological habit and characteristics of Trichobilharzia cercariae in the Huaihe river system. Methods During June of 2002-May of 2003, Radix auricularia snails were collected monthly in Yaohe Fishery of the branch of the Huaihe River. The cercariae, released from the positive snails and collected by Shade Drop Bottle, were examined by direct press. Ducklings were infected by cercariae with different ages and examined for the infection by miracidia hatching method.Results The results showed a typical seasonal fluctuation in infection rate of the snails, i.e. the cercariae detection rate was 0.81% in July, 0.65% in June, 0.07%-0.26% in April, May, August, September and October respectively, with a significant difference (χ 2=26.73, P<0.01). The release of cercariae from the snails showed a diurnal pattern in the natural conditions, with a significant peak between 8:00-12:00. It was proven that the main factors affecting the emerging of cercariae were temperature and light. The cercariae showed positively phototaxis. It was also showed that 50% mortality of the newly released cercariae between 18-25℃ occurred at 41h, and all cercariae died within 52h. The infectivity of cercariae was age-dependent. Under 18-25℃, the highest infectivity was found at 0.5-8h after emergence, then declined steadily to negative by 40 h post-emergence. Conclusion The ecological characteristics of Trichobilharzia cercariae have been preliminarily verified in the Huaihe river system.

Key words: Trichobilharzia, Cercariae, Ecology, Huaihe river