Abstract: Objective　To observe the morphological changes in the testes and ovaries of adult 12th?generation Oncomelania hupensis bred for 12 winters in Weishan Lake areas. Methods　The offspring of the adult O. hupensis snails bred in the Weishan Lake that were originated from the Yangzhou section of the Yangtze River was defined as the experiment group, while uninfected, adult O. hupensis snails captured from the marshland of the Yangzhou section of the Yangtze River served as the control group. Snails were dissected and intact testicular and ovarian specimens were sampled, routinely fixed, dehydrated, embedded, polymerized in an oven and sliced on an ultramicrotome. The sections were visualized under a transmission electron microscope, and the ultrastructure of the snail gonad was compared between the experiment and control groups. Results　Transmission electron microscopy showed “9 + 2” microtubules on the transverse sections of the tails of sperm cells in the testes of male snails in the control group, with triangular acrosomes and spiral, dense nuclei seen in the tip, while in the experiment group, the “9 + 2” microtubules disappeared on the transverse sections of the tails of sperm cells in the testes of male snails, with low chromatin density found in the tip. Transmission electron microscopy revealed clear nucleolus and nuclear membranes in the ova of female snail ovaries, and displayed yolk body, liposomes and endoplasmic reticulum in the cytoplasm, bilayer twists of nuclear membrane and a uniform nucleolus in the control group, while in the experiment group, smooth nuclear membrane and unclear nucleolus were observed in the ova of female snail ovaries, with few contents seen within cells. Conclusions　Following breeding for 12 winters in the Weishan Lake, the 12th?generation O. hupensis snails fail to fully adapt to the natural environment in northern China, and the remarkable changes in the ultrastructure of the snail gonad may be a cause of gradual decline and even extinction of O. hupensis in the Weishan Lake areas.

Key words: Oncomelania hupensis, Gonad, Transmission electron microscopy, Ultrastructure, Weishan Lake

摘要： 目的　观察在微山湖区螺笼放养12个冬季、繁殖12代的成年钉螺睾丸、卵巢形态变化。方法　以亲代来源于长江扬州段的微山湖子代成年钉螺为实验组，以长江扬州段江滩阴性成年钉螺为对照组，解剖两组钉螺获得完整的睾丸和卵巢标本。以常规方法固定、脱水、包埋标本，烘箱内聚合，用超薄切片机常规切片，取切片在透射电子显微镜下拍照和观察，比较两组钉螺生殖腺超微结构。结果　对照组钉螺精子细胞尾部横切面可见“9 + 2”微管结构，头端可见三角形顶体和呈螺旋形且致密的核质；实验组钉螺精子细胞尾部横切面“9 + 2”微管结构消失，头端染色质密度稀疏。对照组钉螺卵巢卵细胞核仁、核膜清晰，细胞质内可见卵黄体、脂质体、内质网，核膜为双层曲折，核仁均匀；实验组钉螺卵巢卵细胞核膜光滑，核仁不明显，细胞内含物更加稀疏。结论　经过12个冬季放养，钉螺不能完全适应中国北方的自然环境，其生殖腺超微结构发生了明显变化，这可能是微山湖区放养钉螺逐步减少甚至趋于消亡的原因之一。

关键词: 钉螺, 生殖腺, 透射电子显微镜, 超微结构, 微山湖区