The studies of histological and ultrastructural characteristics of gonad in the protandrous black porgy, Acanthopagrus schlegeli
| Autor: | Jing-Duan Huang, 黃靜端 |
|---|---|
| Rok vydání: | 2002 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 90 Black porgy, Acanthopagrus schlegeli, is a marine protandrous hermaphrodite. They are functional males at the first and the second spawning seasons, while part of them start to sexually change and become functional females at the third spawning season. The objectives were to investigate the ontogenic pattern of the gonadal structures and the development and ultrastructural changes of the germ cells and somatic tissues in both testes and ovary by light microscopy, scanning and transmission electron microscopy. According to the observations, the reproductive season of black porgy was defined into four stages: post-spawning period (from April to May), resting period (from June to September), pre-spawning period (from October to November) and spawning period (from December to March). The ovarian cavities began to be found in the gonads of four-month-old (July) fish. Very few germ cells could be found during this stage. Generally spermatogonia and oogonia could not be found until six-month-old (September). They located in the ventral part and inside the ovarian cavity of the gonad, respectively. Spermatogonia could not be distinguished from oogonia by light microscopy. Zone of connective tissues, constituting part of the wall of ovarian cavity, separated the testicular tissues from the ovarian tissues. The proliferation of testicular tissues started in October and a few oocytes inside the ovarian cavity also could be found. Development of male germ cells was classified into four stages: spermatogonia, spermatocytes, spermatids and spermatozoa. Male germ cells were arrested in the spermatogonia stage during the resting period. Spermiogenesis included a series of cytological changes: casting of spermatocyte cytoplasm, the 9+2 flagellum structure developing and elongating from the distal centriole, nucleus rotating and the diplosome invaging into nucleus. Both female germ cells and somatic tissues differentiated and proliferated from primordial germ epithelia, which were found in one side of ovarian cavity. After the first spawning spawning, ovarian lamella, the unit of ovary, began to develop. Development of female germ cells was classified into four stages: oogonia phase, chromatin-nucleolus and perinucleolar phase, cortical alveoli and vitellogenic phase and maturation and ovulation phase. Oogonia phase was very short. Female germ cells were nearly arrested in the perinucleolar phase before fish proceeded to sexually change. Granulosa cells surrounded the perinucleolar oocytes and directly contacted with them. When fish proceeded to sexually change, perinucleolar oocytes started to go into vitellogenesis in the prespawning period. Then zona radiata began to appear between granulosa cells and oocyte. Following the processes of the maturation of oocytes, zona radiata grew into three zones: Z1, Z2 and Z3. Microvilli, elongating from oocytes and penetrating through the zona radiata, entered into granulosa cells. Consequently, the cytoplasm of granulosa cells became electron polarization. Blood vessel system played an important role in dynamic variation of the gonadal structures. Main artery and vein appeared in the zone of ovary. Each oocyte was connected with a single group of capillaries, which were then distributed on the surface of the follicular layer. Lots of small blood vessels could be seen within the partially emptied testis after spermiation. The lobular structures and blood vessel system were still intact in the regressed testis of male fish in the resting period. On the contrary, they became disintegrated in the residues of testis of the female fish. In conclusion, these findings provide the important and fundamental cytological and histological basis for the further studies of ultrastructural changes in bisexual gonad and mechanism of natural and controlled sex change. |
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