Abstract：
Osteoglossomorpha, the bony tongue fishes, show great variation in morphology, behavioural strategies, reproductive biology and gamete ultrastructure. The order Osteoglossiformes is the only vertebrate taxon, in which four types of sperm (monoflagellate, biflagellate and aflagellate aquasperm and the complex introsperm) have been described. It is also the only vertebrate lineage in which aflagellate spermatozoa exist. The aim of this study was to analyse the structure of the testis and the process of spermiogenesis in the mormyrid Campylomormyrus compressirostris during the breeding season using light and electron microscopy (transmission and scanning). Males of this species have a single testis of the anastomosing tubular type. The tubules of the anterior part of the testis contain cysts with developing germ cells, and this region is much wider than the posterior part, which consists of efferent ducts filled with sperm cells. The cysts are filled with single or mitotic spermatogonia, primary and secondary spermatocytes and early spermatids. At the stage of spermatids with fine granular chromatin, the cysts rupture and successive stages of spermatid differentiation take place in the testicular lumen; we therefore characterise this process as \'extracystic spermiogenesis\'. Sperm development in C. compressirostris is extremely simple and involves chromatin condensation in the central region of the nucleus, a slight decrease in nuclear volume, the appearance of numerous vesicles in the cytoplasm that form a tubular-vesicular system at the base of the nucleus. Both centrioles and mitochondria are translocated to the peripheral region of the midpiece, which forms the opposite pole to the nucleus. There are many differences between the types of spermiogenesis described so far in teleosts and that found in C. compressirostris, including the loss of flagellum formation. This unique type of spermiogenesis is restricted to species of the families Mormyridae and Gymnarchidae, all of which possess aflagellate spermatozoa. Our data demonstrate that the spermatid differentiation and existence of the aflagellate spermatozoon are a unique phenomena not only among teleosts but also in the whole vertebrate lineage.
摘要：
骨管瘤,多骨舌的鱼，在形态上表现出很大的变化，行为策略，生殖生物学和配子超微结构。骨鳞翅目是唯一的脊椎动物分类单元，其中四种类型的精子(单鞭毛，已经描述了双鞭毛状和无鞭毛状水生植物和复杂的内胚乳）。它也是唯一存在无毛精子的脊椎动物谱系。这项研究的目的是使用光学和电子显微镜（透射和扫描）分析繁殖季节中的睾丸结构和精子生成过程。该物种的雄性具有吻合的管状类型的单个睾丸。睾丸前部的小管包含有发育中的生殖细胞的囊肿，这个区域比后部宽得多，由充满精子细胞的输出管组成。囊肿充满了单个或有丝分裂的精原细胞，初级和次级精母细胞和早期精子细胞。在精子细胞具有细颗粒染色质的阶段，囊肿破裂和精子细胞分化的连续阶段发生在睾丸腔中；因此，我们将这一过程描述为“囊外精子发生”。C.compressirostris的精子发育非常简单，涉及细胞核中心区域的染色质凝聚，核体积略有减少，细胞质中大量囊泡的出现，在细胞核的底部形成管状囊泡系统。中心粒和线粒体都转移到中段的外围区域，形成与原子核相反的极。到目前为止，在硬骨鱼中描述的精子发生类型与在C.compressirostris中发现的精子发生类型之间存在许多差异，包括鞭毛的损失。这种独特的精子发生类型仅限于Mormyridae和Gymnarchidae的物种，所有这些都有无尾藻状精子。我们的数据表明，精子的分化和无毛精子的存在不仅在硬骨鱼中而且在整个脊椎动物谱系中都是独特的现象。
