Spermatogenesis and Morphology of the Male Reproductive Tract of the Turtle Kinosternon scorpioides.

The scorpion mud turtle (Kinosternon scorpioides), a freshwater chelonian widely distributed in South and Central America, presents gaps in the microscopic and ultrastructural characterisation of its male reproductive system. This study provides a comprehensive characterisation of the testes, epididymides, and deferent ducts of adult males collected during the rainy reproductive season in the Brazilian Amazon. Morphometric parameters were recorded and showed a positive association between body weight and reproductive tract mass, supporting increased gonadal investment during the breeding period. Tissues were processed for light microscopy (LM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Histological and ultrastructural analyses revealed active spermatogenesis, abundant germ cells in multiple developmental stages, and regionally specialised epithelia along the epididymis and deferent ducts. Spermatozoa exhibited preserved acrosomal, nuclear, mitochondrial and axonemal structures, indicating functional integrity and short-term storage capacity within the male reproductive tract. These findings expand current knowledge of chelonian reproductive biology and provide essential baseline data to support assisted reproductive technologies and conservation strategies for K. scorpioides and related freshwater turtle species.