Histochemical and immunohistochemical analysis of testicular morphology and spermatogenesis in Gymnotus carapo (Teleostei: Gymnotidae)

This work aims to study the testicular morphology and spermatogenesis of Gymnotus carapo to provide information on their reproductive biology which is useful in managing this species as a fishing resource. The testicles were isolated and fixed in 10% formalin; subsequently, they were processed for scanning electron microscopy with conventional histological technique. To analyze the cell proliferation of germline cells and Sertoli cells, immunodetection of the proliferating cell nuclear antigen (PCNA) protein was performed. In G. carapo spermatogenesis, the spermatogenic line is organized into cysts. Spermatogonia A is characterized by more bigger and solitary cells. Spermatogonia B are smaller cells; their nucleus has a larger area concerning the cytoplasm and is grouped in tubules. Spermatocytes (I–II) are smaller than spermatogonia in the prophase of meiotic division. Spermatids are cells with dense, rounded nucleus. The sperm were found in the lumen of the tubule. By immunostaining PCNA, it was possible to observe the proliferative activity of germ line cells and Sertoli cells during the cyst reorganization phase. These results are the basis for future studies focusing on the analysis compared to females of the reproductive cycle of G. carapo.