Spermatogenesis and Spermatozoon Ultrastructure in the Nile Pebblyfish Alestes dentex (Teleostei: Characiformes: Alestidae) PDF

Keywords

Spermatogenesis, sperm, Alestes dentex, ultrastructure, morphology, haraciformes

Abstract

The ultrastructure of spermatogenesis and spermatozoon of Alestes dentex is described by using scanning and transmission electron microscopy. The testis is lobular in shape and spermatogenesis is of the unrestricted type. The germ cells are found in clusters within the seminiferous tubules and surrounded by a cytoplasmic processes of the Sertoli cells. Spermiogenesis is characterized by chromatin condensation, flagellum development, nuclear rotation, migration of the diplosome and mitochondria to the basal pole of the nucleus, nuclear indentation, nuclear fossa formation and loss of the excess cytoplasm. The mature spermatozoon is of the primitive type; type I aquasperm. The spermatozoon has no acrosome and has a rounded head with a heterogeneously electron-dense nucleus, which contains a deep axial nuclear fossa and a nuclear notch. The nuclear fossa contains the centriolar complex and part of the basal body of the axoneme. The short midpiece contains a mitochondrial ring, which consists of several unequal-sized and unevenly distributed mitochondria. The flagellum has the classical axoneme pattern of 9+2 and has no lateral fins or a membranous compartment. In addition, the spermatozoon has some peculiar features, which are not previously described in Characiformes and include the presence of two fibrous bodies anchoring the proximal centriole to the nucleus, a thick outer membrane of dense fibers separating the flagellum from the cytoplasmic canal and a basal foot and alar sheets attaching the basal body to the nucleus and plasma membrane. These findings suggest that the ultrastructural features of spermiogenesis and spermatozoa of A. dentex are synapomorphy of Ostariophysi, Perciformes, and Salmoniformes