Characterization of lake minnow Eupallasella percnurus semen in relation to sperm morphology, regulation of sperm motility and interpopulation diversity.

Sperm morphology and regulation of sperm motility of lake minnow Eupallasella percnurus, an endangered cyprinid, were investigated. Milt characteristics from two isolated populations of E. percnurus were compared to characterize the interpopulation diversity. Electron microscopic studies revealed that E. percnurus spermatozoa comprise simple, uniflagellate, anacrosomal aquasperm with species-specific features as an eccentrically located implantation of nuclear fossa and eccentric insertion of flagellum. Sperm motility was significantly inhibited by relatively low ion concentrations (150, 150 and 8 mM for NaCl, KCl and CaCl2 , respectively). Sperm maintained a high motility rate over a wide pH range (5.5-10.5), which may reflect adaptation to a highly variable environment. The two E. percnurus populations were markedly different in milt volume, sperm concentration, seminal plasma pH, sperm motility and beat cross frequency, which may result from genetic differences and environmental conditions.

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 internally inseminating characid fish, Mimagoniates barberi. Our ultrastructural study revealed that sperm bundles of both types are formed within the efferent ducts of the posterior, aspermatogenic part of the testis. The epithelial 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 and vacuoles abound in the cytoplasm. Adluminal surface of the epithelial cells often exhibits extensions of various form. Two types of secretions are present in the efferent ducts. In more proximal ducts the secretion is finely 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. In the most caudal portion of the testis where only fully formed sperm bundles of both types are present no structured secretion in the lumen of the efferent 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.