ULTRASTRUCTURAL COMPOSITION OF STEROID PRODUCING CELLS IN OOCYTE WALL, AND MICROPYLAR APPARATUS AS A SPERM GUIDANCE SYSTEM IN OREOCHROMIS NILOTICUS REARED IN FRESHWATER ENVIRONMENT

ULTRASTRUCTURAL COMPOSITION OF STEROID
PRODUCING CELLS IN OOCYTE WALL, AND MICROPYLAR
APPARATUS AS A SPERM GUIDANCE SYSTEM IN
OREOCHROMIS NILOTICUS REARED IN FRESHWATER
ENVIRONMENT
ZAKI M.I., AZIZ F.K. AND ABOU SHABANA N.M.
THE NATIONAL INSTITUTE OF OCEANOGRAPHY AND FISHERIES, ALEXANDRIA.
Key words: Oocyte ultrastructure, steroid producing cells, Oreochromis niloticus, spermatozoa,
micropylar apparatus.
ABSTRACT
The oocyte wall includes several steroid producing cells such as thecal and granulosa
cells. On the prosecution of these cells, it was found that their ultrastrucutral composition
permit them to produce steroids which are important in the continuity of oogenesis. The
wall of the perinucleolar stage shows one layer of follicular epithelial layer with oval nuclei
separated from the cytoplasm by a basal lamina. The epithelial follicle of vacuolized oocyte
increased in thickness and differentiated into an outer thecal layer with clear basal lamina
and an inner granulosa layer. In yolk deposition ocyte a considerably high nucleoplasmic
ratio is displayed in the thecal cells. The granulosa layer has an amoeboid large nucleus
displaying a granular electron dense chromatin arranged on its periphery with a clearly
detected uniformly electron dense nucleoli located near the nuclear membrane. The
granulosa’s cytoplasm is characterized by the existence of plentiful number of
mitochondria and a network of smooth endoplasmic reticulum. The thecal cells of tertiary
yolk deposition oocyte show a considerable amount of secreted oil or lipid droplets, larger
sized oval mitochondria and clearly detected golgi bodies. Ripe ova wall shows a
tremendous number of mitochondria in the granulosa cells in which they are scattered
filling the whole cytoplasmic area.
The spermatozoa of Oreochromis niloticus have long flagellar tail reaching 18 in length
and the head’s diameter ranges between 1.5-1.3 along its long and short axes. The ripe
oocyte wall of the studied fish has a non-adhesive wall with floor tiles- like pores and a
special micropylar apparatus including cristae corresponding to similar irregularities in the
sperm head ,such pattern could act as a sperm guidance system.