埃及尼罗河鲶的精子发生和精子的超微结构

用扫描和透射电子显微镜研究了尼罗河鲶——盾头歧须鮠(Synodontis schall)的精子发生和精子的超微结构。精巢中含有无数肾形的生精小叶,我们将其称为"精原无限型"。尽管其精子发生的大体过程与同类鱼无异。但是,在细节上仍具其独特之处。这些特点未见在其他硬骨鱼中报道过。其特点主要是:生精过程中不发生细胞核的旋转,中心粒复合体和轴丝起始段直接发生在核的基底面垂直线上,有无数的粗的固定纤维将近端中心粒和远端中心粒的近侧部连接到细胞核上。另外,精子发生过程中还包括染色质浓缩,细胞质和线粒体向细胞核的尾端迁移,在核的后端中轴位置上形成中等大小的核后凹,近端中心粒和远端中心粒的一部分嵌在核后凹之内,短的胞质内陷管将线粒体与鞭毛分隔开。精子头部接近圆形,无顶体或顶体泡,鞭毛的中段及胞质内陷管均较短,整个鞭毛却很长,鞭毛侧面无翼膜,轴丝呈典型的9 2结构。上述结果显示,盾头歧须鮠的精子发生具有类型Ⅰ和类型Ⅱ的共同派生特征,这种特征在常见的其他硬骨鱼中也是常有的。但是,正如文献所报道过的另两种尼罗河鲶——金鯵(Chrysichthys auratus)和电鲶(Malapterurus electricus)中的情况一样,盾头歧须的精子发生与类型Ⅲ的精子发生过程更为相似。

Spermatogenesis and spermatozoon ultrastructure in the Nile catfish Synodontis schall(Pisces: Actinopterygii: Synodontidae)in Egypt

Spermatogenesis and spermatozoon ultrastructure in the Nile shield-head catfish Synodontis schall are described using scanning and transmission electron microscopy. The testis consists of numerous finger-like spermatogenic lobes and its structure is described as "unrestricted" spermatogonial type. Spermatogenesis does not show any special peculiarities; however, spermiogenesis exhibits some peculiar features, which are not previously described among teleosts for which data are available, excepting the Nile catfishes examined so far. Among these features are: absence of the nuclear rotation and development of the centriolar complex and the initial region of the axoneme in a position directly perpendicular to the basal pole of the nucleus and presence of numerous thick anchoring fibrils connecting the proximal centriole and the proximal part of the distal centriole to the nucleus. In addition, spermiogenesis includes chromatin condensation, migration of the cytoplasm and mitochondria to the caudal pole of the nucleus, formation of a moderate axial nuclear fossa containing the proximal centriole and part of the distal centriole and presence of a short cytoplasmic canal separating mitochondria from the flagellum. The spermatozoon has a more or less round head with no acrosome or acrosomal vesicle, a short midpiece with a short cytoplasmic canal and a very long tail or flagellum that lacks lateral fins and a membranous compartment and exhibits the classical 9+2 axoneme pattern. These findings suggest that spermiogenesis in S.schall is a synapomorphic type derived from types Ⅰ and Ⅱ spermiogenesis which are common among other teleosts and is closely similar to type Ⅲ spermiogenesis that is previously described in the Nile catfishes Chrysichthys auratus and Malapterurus electricus.