Ultrastructure of Sorubim lima (Teleostei, Siluriformes, Pimelodidae) spermiogenesis.

The spermiogenesis and the spermatozoon ultrastructure of Sorubim lima were studied. Our observations showed that early spermatids are round-shaped cells, have spherical nucleus with diffuse chromatin, small quantity of mitochondria and large amount of vesicles in the cytoplasm. During the differentiation process in the nucleus, chromatin compacts in a progressive and homogeneous way, and the flagellum is formed. In the cytoplasm the vesicles, that have double membranes, aggregate and fuse on the plasma membrane. The spermatozoa of S. lima have no acrosome and show spherical nucleus with homogeneous and highly compacted chromatin, intermediary piece with mitochondria and double wall vesicles contiguous to the plasma membrane, as well as a flagellum formed by a basic axoneme (9 + 2).