Sperm morphology and distribution of intramembranous particles in the sperm heads of selected freshwater teleosts.

The morphology of spermatozoa and the distribution of intramembranous particles (IMPs) in sperm-head membranes in teleostean fish were examined ultrastructurally to clarify the presence of characteristic arrays (parallelogram or hexagon in packing) of IMPs. The following four species of fish were used: goldfish (Carassius auratus), loach (Misgurnus anguillicaudatus), flat bitterling (Acheilognatus rhombeus), sweetfish (Plecoglossus altivelis). It was demonstrated that spermatozoa of all these fish were devoid of an acrosomal structure in the anterior portion of the head. Spermatozoa had round heads in goldfish, loach and flat bitterling. Two centrioles (proximal centriole and basal body) were present and located adjacent to each other in all fish. The characteristic arrays of IMPs were found in spermatozoa of goldfish and flat bitterling. IMPs were more numerous on the P-face than on the E-face in all species. The present work showed that the characteristic arrays of IMPs were not common structures in spermatozoa of teleostean fish.