Abstract: Total number of 76 Pseudobagrus fulvidraco(Richardson)caught in Huangzhou along the Yangtze River from June to July in 1998 were examined for infection by Brentisentis yangtzensis. The infection rate of the host was 30.3% and the intensity of infection was 60. The infection rate of female host was higher than that of male,but the difference of parasite intensity between female and male host was not significant. The parasite intensity of the host with body length within 23cm increased notably with increasing of the body length,but the parasite intensity of the host with body length above 23cm decreased rapidly and no Brentisentis yangtzensis was found in the host with body length above 31cm. Distribution of Brentisentis yangtzensis was clumped in the host population. The 90.3% of the parasite was distributed in first 1/3 intestinal portion of the host. The population structure pattern of the parasite looked like a pyramid. The parasitism did not cause obvious difference of condition factor in the hosts.

Key words: Camellia meiocarpa, C. oleifera, genetic differentiation, introgressive hybridization.