Ultrastructure of the epithelial cells in the aspermatogenic part of the testis in Mimagoniates barberi (Teleostei : Characidae : Glandulocaudinae) and the role of their secretions in spermatozeugmata formation

Two types of unencapsulated sperm bundles are present in the milt of the in ternally inseminating characid fish, Mimagoniates barberi. Our ultrastructu ral study revealed that sperm bundles of both types are formed within the e fferent ducts of the posterior, aspermatogenic part of the testis. The epit helial cells of the testicular tubules of the aspermatogenic portion of M. barberi testis show signs of both secretory and phagocytic activity. Rough endoplasmic reticulum, polyribosomes, Golgi complexes, secretory vesicles a nd vacuoles abound in the cytoplasm. Adluminal surface of the epithelial ce lls often exhibits extensions of various form. Two types of secretions are present in the efferent ducts. In more proximal ducts the secretion is fine ly granular, whereas in more distal ducts groups of coalescing spermatozoa are accompanied by a fibrous secretion. The sperm are aligned along strings of this secretion which is most probably instrumental in sperm clumping. I n the most caudal portion of the testis where only fully formed sperm bundl es of both types are present no structured secretion in the lumen of the ef ferent ducts is found. No secretion between the sperm within the bundles is visible. The results of histochemical staining indicate that the secretion in the tubules has no carbohydrate component and is proteinaceous.