Morphology of the male genitalia and sperm fine structure in siluroid fish.

Morphology of male genitalia and sperm fine structure of 4 siluroid fish, Callichthys thoracatus (Callichthyidae), Dysichthys coracoideus (Aspredinidae), Mystus armatus (Bagridae) and Ancistrus triradiatus (Loricariidae) were studied. In Dysichthys coracoideus and Ancistrus triradiatus the male genitalia consisted of paired testes and spermatic ducts but had no seminal vesicles. In Callichthys thoracatus the male genitalia had also paired seminal vesicles which were separated from the testis and emptied into the spermatic duct. Also in Mystus armatus seminal vesicles were found. They were not separated from the testes but the seminiferous tubules changed into seminal vesicle lobes which finally emptied into the spermatic ducts. All the investigated species had simply organized aquasperms typical for external fertilizing teleosts which were characterized by an ovoid or elliptoid head, by a small midpiece and by the absence of an acrosome. The spermatozoa of Dysichthys coracoideus and Mystus armatus were biflagellate, while they were monoflagellate in Ancistrus triradiatus and Callichthys thoracatus. The proximal centriole was reduced in Dysichthys coracoideus and Mystus armatus and the basal body attached to the nucleus. Single mitochondria were found in Dysichthys coracoideus, Ancistrus triradiatus, and Callichthys thoracatus. On the contrary, in Mystus armatus mitochondria were fused to a more complex chondriosome.