A histochemical and ultrastructural study of oogenesis in Aristaeomorpha foliacea (Risso, 1827)

Ovaries from mature giant red shrimp Aristaeomorpha foliacea were investiga ted histochemically and ultrastructurally. Four growing stages of the oocyt es were distinguished: premeiosis stage, previtellogenetic stage, early vit ellogenic stage and late vitellogenic stage. In addition, occasional resorp tive oocytes were found. Oogonia and premeiotic oocytes were found in germi native zones. Previtellogenic and vitellogenic oocytes were localized in ma turative zones. As vitellogenesis proceeded, oocytes showed a progressive d evelopment in the number of lipid droplets as well as in the extension of R ER, constituted of dilated cisternae, uniformely scattered throughout the c ytoplasm. The RER produced yolk granules and a lampbrush-like substance. Th e latter was released under the oolemma and constituted a characteristic co rtical zone. The oolemma did not develop microvilli or micropinocytotic ves icles to incorporate yolk precursors. Thus, the protein yolk appeared to be of endogenous origin. Few somatic cells were found around the oocytes, but they never gave place to a continuous epithelial layer around oocytes, thu s it is not possible to speak of ovarian follicle. The cytoplasm of these m esodermal-oocyte associated cells (MOAC) was characterized by a typical ste roidogenic apparatus. Few resorptive immature oocytes were found inside lat e vitellogenic oocytes. Since the ovaries were packed with late vitellogeni c oocytes and the few immature oocytes were hardly detectable, oocyte matur ation occurred in a synchronous way.