Abstract: To explore the change of reproductive system in morphology and tissue structure of Parafossarulus striatulus during the cyanophyterial blooms of Taihu Lake, this study examined the reproductive system structure of male and female of Parafossarulus striatulus during the cyanophyterial blooms stage and non-blooms stage in the Suzhou Bay（SZ）, Gonghu（GH）, Meiliang Bay（ML）, and Zhushan Bay（ZS）by the methods of anatomy and routine paraffin section. The results showed that the males lacked penile ducts in appearance during the cyanophyterial blooms stage. Respectively, the numbers of spermatogonium, spermatocyte, spermatid, spermatozoa of cyanophyterial blooms stage were reduced by observing the gonadal tissue sections. There was no significant difference in the degree of imposex between the two sampling sites in Suzhou Bay（SZ）and Meiliang Bay（ML）during cynobacterial blooms stage of Taihu Lake, while the degree of imposex was higher than Zhushan Bay（ZS）, and Gonghu（GH）was the lowest. There was no significant difference in morphology and gonadal tissue structure between the two groups of female Parafossarulus striatulus .

Key words: Taihu Lake, cyanophyterial blooms stage, Parafossarulus striatulus, imposex