Description of spermatogenesis and sperm ultrastructure of Acanthostomum (Atrophocaecum) aswaninesis Wannas, 1977 (Digenea, Acanthostomatidae), a parasite of Bagrus bayad in Egypt

Spermatogenesis and the spermatozoon of Acanthostomum (Atrophocaecum) aswaninesis, were studied by transmission electron microscopy. Spermatogonia characterized by a large nucleocytoplasmic ratio, give rise to two generations of spermatocytes. The secondary spermatocytes divide forming early spermatids that fuse together into a common cytoplasmic mass. Spermiogenesis begins with the formation of the zone of differentiation in front of 2 centrioles associated by an inter-centriolar body. Each centeriole is linked to striated rootlet, and gives rise to a flagellum. It is characterized by an asynchronic flagellar rotation and subsequent proximodistal fusion with a median cytoplasmic process. The spermatozoon is formed after constriction of arched membranes. Mature spermatozoon of A. (A.) aswaninesis is filiform, tapering at both ends and it presents all the characteristic features found in the digenean gametes. The spermatozoon possesses 2 axonemes of the 9+ ‘‘1’’ pattern, a nucleus, mitochondria, glycogen and two bundles of parallel cortical microtubules. A major feature is the presence of external ornamentation in the anterior part of the mature spermatozoon, and the presence of two mitochondria rather than just (1) as in most of the digenean spermatozoon. The spermiogenesis process and spermatozoon organization of A. (A.) aswaninesis match the general pattern found in the digenea, but certain peculiarities are characteristic and differentiate the sperm of this fluke from that of other digenetic trematodes.