Structure and cytology of the testes of Labeo victorianus (Pisces: Cyprinidae)

Abstract

Testes macromorphology and histomorphology together with sperm cytology are described for a potamodrometic cyprinid fish, Labeo victorianus, from Lake Victoria. Testes were found to be paired and elongate, suspended by a mesorchium on either side of the swim bladder. A sperm duct ran along the medial surface of each testis before fusing caudally to form the common sperm duct that terminated at the  urogenital pore. Main sperm ducts were lined by simple columnar epithelium  supported by a wall with elastic connective tissue and a few smooth muscle cells. The tunica albuginea divided the testes into lobules, which contained spermatogenetic cell types. The lobules, released spermatozoa into an anastomosing tubule network that emptied directly into the main sperm duct. Valve like structures were present along the length of the sperm duct and are proposed to regulate milt flow. Three types of somatic cells were observed at the onset of gonadal recrudescence; plasma and intralobular somatic cells were within the  lobules, while Leydig cells were close to the blood vessels in the interstitium. Maturing testes were characterized by the dominance of spermatocytes and spermatids, both contained in cysts. Spermatozoa, arising from the spermatids, filled the lobular lumen in mature testes after spermatocyst rupture. In post spawned testes, Type A spermatogonia dominated. Testicular regression was not characterized by spermatozoa phagocytosis, rather via apoptosis.

Key words: gonadal morphology, spermatogenesis, apoptosis, testicular  recrudescence.