Abstract
This study investigated the spermatogenesis of the freshwater stingray Potamotrygon motoro using microscopic analyses. The testes of this species were described as being composed of germinal zones, a degenerated zone, and the epigonal organ, consisting of connective tissue and lymphomyeloid cells. A cystic pattern of spermatogenesis was observed, in which each cyst is formed and maintained by Sertoli cells that undergo morphological and positional changes throughout the process. After the release of spermatozoa into the duct, the peripheral cysts formed a degenerating layer. Spermiogenesis, the final phase of sperm development and differentiation, was identified as a complex process in P. motoro, involving nuclear compaction and structural modifications. This study presents, for the first time, a detailed description of the germ cell development process in P. motoro, contributing to the understanding of spermatogenesis in freshwater stingrays.