Ultrastructural features of germ cells in immature swordfish Xiphias gladius (Teleostei: Xiphidae)

The presence of perinuclear nuages and intercellular bridges is described in the germ cells of immature Xiphias gladius. In semithin sections, previtellogenic oocytes show a strongly basophilic perinuclear area. At the ultrastructural level this zone appears as a cytoplasmic granulo-fibrillar substance in the form of a crescent cap adjacent to the nuclear membrane: the perinuclear nuage. A material similar to the perinuclear nuage is first observed in the nucleolus, then close to the nuclear envelope, and later on is associated with mitochondria. Perinuclear nuages could consist of RNA and proteins involved in the development of oocytes. Electron microscopy analysis of the testicular germ cell showed the presence of annulate lamellae in primary spermatogonia and intercellular bridges, originating from incomplete cytokinesis, in the secondary spermatogonia. In spite of numerous studies on annulate lamellae, their function is not well understood. The intercellular bridges provide channels for communication between the members of a germ-cell clone and probably synchronize the simultaneous entry of the cells into the subsequent mitosis