Oogenesis And Early Development Of Siniperca Kneri Garman

From Mar. 2005 to Feb. 2006, 260 specimens of Siniperca kneri Garman were collected from Hechuan reach of Jialing River. The development of ovary and oogenesis were studied by anatomy, histology and histochemistry, also the early life history Siniperca kneri were observed. The results were as follows:Based on shape, external color and size, the development of ovary S.kneri was divided into five stages. Ovaries in stage I were transparent. In stage II, the ovary was fresh and semi- transparent. As for the stage III, it was flat and cystiform, and then became club- shaped. As for the stage IV, the eggs were evident, and the ovary was packaged with membrane. Then in the last stage, namely stage V, eggs were dividing. When the abdomen of S.kneri was pressed, there would be eggs flowing out of the abdomen. By means of histology, the development of S.kneri could be divided into five phases according to the existence or absence of spawning plate, the color and the number of nucleolus. The first stage was oogonium, in which cytoplasm had no basiphilic, but was strongly acidphilic. It had a large nucleus-to-cytoplasm ratio, double layers of nuclear membrane, a central nuclear and a big central nucleolus. Then came the Oocyte Phase., where no sporadic follicle cells were observed. The volume of oocyte and the number of nucleolus increased, at the same time, the yolk vesicle appeared. The third was oocyte with yolk globules. The yolk vesicle reached to several layers gradually, with the appearance of yolk granules. Outside of the oocyte, there were two layers of follicle cells. In the fourth phase, oocyte was filled with yolk granules. It had three layers of follicle cells. The fifth one was the phase of mature oocyte. The volume of the oocyte was the largest, with follicle cells and oocyte separated. Histochemical study gave the following results: glucide, fat, protein decreased first, increased later with the extension of oogenesis. By the means of transmission electron microscope, the development of oogenesis was divided into five phases on the basis of vitellogenesis and the change of egg envelop. First, the phase of oogonium, the oogonium was round with a big central nucleolus. Nucleus-like bodies clung to the nuclear membrane. There were a lot of mitochondrium in the cytoplasm. Second, the phase of previtellogenesis, the number of nucleolus increased, with vesicals in the nucleolus. Mitochondrium had moved to the cytoplasm, forming "mitochondria cloud". There were two layers of follicle cells, basic layer lying between them. Microvilli were sticked out of the oocyte and follicle cells. Z1 was formed closing to the oocyte. Third, the phase of early period of vitellogenesis, the number of organelle aggrandized rapidly, altered. There were three layers of follicle cells, designated outer thecal cell, inner thecal cell and follicer cells. Three layers of zone radiata formed, named Z1, Z2 and Z3. Fourth, the phase of late period of vitellogenesis, where all kinds of organelles were activated to vitellogenesis. There were four types of yolk plates altogether. Fifth, the phase of mature oocyte. The volume of oocyte came to the largest. The oocyte was filled with yolk granules. The yolk granules had different volume, moreover, the least yolk granules tended to form the bigger one.The eggs of S.kneri were no sticky, almost spherical in shape, transparent and unpigmented, with 1 or 1-6 oil globules in pale yellow yolks, and they were about 0.5-1.0mm in diameter, but 2.1-2.2mm after absorbing water. According to the morphological characters of embryos and differentiation, embryonic development was devided into Precleavage, Cleavage, Blastula, Gastrula, Neurula, Differentiation period of organ, Hatching. When water temperature is 13.9-19.8℃, 183.3h were needed to hatch the embryos. Newly hatched larvae have a total length of 4.6-5.2mm with about 32-35 myomeres. The fertilized eggs by artificial fertilization were studied as regarding their postembryonic development and larva growth. The development of larval S.kneri can be divided into yolk-sac larva, late-stage larva and juvenile stage. Newly hatched larvae have a total length of 4.6-5.2mm with about 32-35 myomeres. About 45-50d completed changes of the external morphology and internal morphogenesis under the condition of water temperature ranged from 26.5-29.5℃. There existed a linear relation model between total length and age (days) in larval stage. The regression equation as follow: L=0.7865t+1.3275 (R~2=0.9696) , and the ratio of total length to post anus length was between 1.63-2.08.