Ultrastructural studies of spermatogenesis and the functions of Leydig cells and Sertoli cells associated with spermatogenesis in Larimichthys polyactis (Teleostei, Perciformes, Sciaenidae)

Ultrastructural studies of spermatogenesis and the functions of Leydig cells and Sertoli cells were investigated by electron microscope observation. Ultrastructural characteristics of spermatozoa of Larimichthys polyactis (Sciaenidae) have a round head, a nucleus containing highly compact filamentous clusters of chromatin, slightly eccentric nuclear fossa, no acrosome, a short midpiece with a short cytoplasmic channel, and a flagellum showing the classic axoneme structure (9 + 2) and short irregular flagellum lateral fins. The spermatozoon of this species (Sciaenidae) is Perciformes type II: the flagellar axis is parallel to the nucleus, the centriolar complex is outside the nuclear fossa, the proximal centriole is anterior and perpendicular to the distal centriole, and no more than five spherical mitochondria are observed. Each of the well-developed Leydig cells observed during the periods of active meiotic division and before spermiation contains an ovoid vesicular nucleus; a number of smooth endoplasmic reticulum, tubular, or vesicular mitochondrial cristae; and several lipid droplets within the cytoplasm. This indicates that Leydig cells, as typical steroidogenic cells showing several cytoplasmic characteristics, are involved in male steroidogenesis. However, no clear evidence of steroidogenesis or of any transfer of nutrients from the cells to spermatids that appears to be associated with phagocytic function in the seminiferous lobule was observed for Sertoli cells. These findings indicate that Sertoli cells of this species function in phagocytosis and the resorption of products originating from degenerating spermatids and spermatozoa following spermiation.