Histologically, no germ cells were identified in 6-mo-old animals, although the germinal epithelium
exhibited a degree of development at some areas of the conical appendage, forming a double cell layer with that of the digestive gland epithelium (Fig.
However, in maturing and spawning bluefin tuna a well-developed network of ducts collects the sperm produced by the germinal epithelium
and voids them into the main sperm duct.
They were a single or formed a cluster on the germinal epithelium
Using image analysis, the percent of germinal epithelium
and nutritive phagocytes and long diameters of oocytes were measured from H&E prepared slides of gonad tissue.
One male from June was in a late stage of spermiogenesis in which the germinal epithelium
was reduced to 5-6 layers, although sperm were still being produced.
Three stages in the testicular cycle (Table 1) were present: (1) regressed (= quiescence), seminiferous tubules contain Sertoli cells and spermatogonia; (2) recrudescence (= recovery), proliferation of cells in the germinal epithelium
is in progress, primary, secondary spermatocytes and, in some cases, spermatids are present; (3) spermiogenesis (= sperm production), lumina of seminiferous tubules lined by spermatozoa; clusters of metamorphosing spermatids are present.
The germinal epithelium
was reduced to a few layers in thickness, occasional metamorphosing spermatids but no spermatozoa were present.
A few rows of metamorphosing spermatids remained in some seminiferous tubules but the germinal epithelium
Males followed a seasonal testicular cycle (Table 1) in which three stages were represented: (1) Regression (non-reproductive) in which the germinal epithelium
is exhausted and the predominant cells are Sertoli cells and spermatogonia; (2) Recrudescence (recovery) characterized by renewal of the germinal epithelium
for the next period of sperm formation; primary and secondary spermatocytes are the predominant cells; (3) Spermiogenesis (sperm production) in which the seminiferous tubules are lined by clusters of spermatozoa and metamorphosing spermatids; the epididymides are packed with sperm.
consisted of a few layers of cells and small clusters of sperm lined the lumina of the seminiferous tubules.
In the regressed testis, the germinal epithelium
is exhausted and the predominant cells are Sertoli cells and spermatogonia.