Study of atresia in the ovary of bagrus bayad during the reproduction cycle by histological and electron microscopic investigation

ABSTRACT

Atretic follicles in ovary of the Nile teleost fish, Bagrus bayad, were followed through out the spawning period. They have been examined under light microscope. Six types of atresia have been distinguished, Two of them have been subjected to the electron microscope examination. In general, atretic follicles have been found in mature and tertiary yolk oocytes stage. They were measured to be larger than 400 micro in diameter. The Observed sequences for atretic follicles were as follows erosion of thecal layer, hypertrophy of granulosa, and finally dissolution of ooplasm. In ultra structure examination erosion of thecal layer appeared as ill-defined cell outline with obvious separation between granulosa and thecal layer. Beside, junction of complex vanished. In addition, the zona radiata ruptured to small fragments. In conclusion atresia in Bagrus bayad is a functional activity of oocyte development which might be influenced by hormonal mechanism that regulate oocyte growth and recruitment