Studies On The Function Of The Pituitary-gonad And Its Regulation-controlling Axis In Cultured Japanese Flounder Paralichthys Olivaceus

In this paper, the pituitary, gonads and sexual steroid hormone of cultured Japanese flounder are studied by the methods of electron microscopy techniques, histological staining techniques, immunohistochemical mehods and radioimmunoassay, the main results and conclusions are as follows:1. Histological study on the ovary and the response of germ cells in ovary ofcultured Japanese flounder to exogenous hormoneThe ovary of cultured Japanese flounder is in stage II in all experimental groups. A mass of phase 2 oocytes are observed under optics microscop. The injection with LHRH-A2 or hCG or LHRH-A₂ plus hCG fails to stimulate more germ cells development in ovary compared with the fish of control group, it is suggested that the response of oocytes to exogenous LHRH-A2 or hCG is lower in that period of time.2. The micro- and ultra-structure study on germ cells and the response ofspermary of cultured Japanese flounder to exogenous hormoneThe spermary of cultured Japanese flounder is lobular type. Gonads of the male experimental fish are almost matured when body length is 24-34cm, and few individuals of maturations are in spermiation stage. Large mumbers of spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids and spermatozoa are observed under electric microscope. The spermatozoon has no acrosome, its tail structure is the style of "9+2". No more spermatozoa increase in seminiferous lobules in male fish injected with LHRH-A₂ or hCG or LHRH-A₂ plus hCG compared with the fish of control group. The results demonstrate that exogenous LHRH-A2 or hCG can not stimulated significantly the development of germ cells in spermary and reproductive process.3. Histological and immunohistochemical study on endocrine cells in thepituitary of cultured Japanese flounderThe shape of the pituitary in Japanese flounder is similar to the heart of chicken, composed of neurohypophysis and adnohypophysis that is divided into RPD, PPD and PI. Using Jafri, HA and Mallory staining techniques, electron microscope techniques and immunohistochemical mehods, the histological structure of the pituitary is observed in details. A mass of PRL and ACTH cells and a small quantity of TSH cells are in RPD, a great deal of GH and GtH and a little TSH are observed in PPD, and besides, MSH cells is in PI. Out of these endocrine cells, GH cells dominate in the number, GtH cells are inactive and ACTH cells are active relatively. No more secretory granule of GtH cells increased when the fish is injected with LHRH-A2 or hCG or their combination, it is suggested that the response of GtH cells to exogenous LHRH-A2 or hCG is lower.4. Effects of exogenous hormone on the plasma T and ï¿¡2 levels in cultured Japanese flounder4.1 The response of plasma testosterone to injection with LHRH-A2 or hCG inmale fishThe plasma T levels decrease significantly post-injection 6 hour, and occure the lowest level at post-injection 12 hour, somewhat increase post-injection 24 hour, and farther increase post-injection 30 hour, but is still lower than the intact fish when male fish is injected with alone LHRH-A2 at dosage of 25ug/kg BW or hCG at dosage of lOOOIU/kg BW. The plasma T level of the fish in control group also decreases as same as these fish treated with hormone. The plasma T levels don't increase when fish injected with LHRH-A2 plus hCG, whereas the lowest value occures at postinjection 24 hour but not 12 hour, and enhances slowly at 30h compared with alone injection. The results suggest that the injection with alone LHRH-A2or hCG or combined LHRH-A2 and hCG fail to increase significantly plasma T levels, on the contrary, suppress T concentration in male Japanese flounder.4.2 The response of plasma estradiol to injection with LHRH-A2 or hCG infemale fishThe plasma E2 levels decrease significantly post-injection 6h, and occure the lowest level at post-injection 24h, somewhat increase post-injection 30h, but is still lower than the intact fish when female fish is injected with alone LHRH-A2 at dosage of 25ug/kg BW. At the same time, the plasma E2 levels of the fish in control group also decrease as these fish treated with hormone. The E2 concentration of the plasma in female fish injected with alone hCG at dosage of lOOOIU/kg BW decreases significantly at postinjection 6h, and unchanged while postinjection 12 to 24h, the lowest value occures at 3 Oh after injection.The plasma E2 levels decrease significantly after injection with LHRH-A2 plus hCG, the lowest value occur at 24h. these results suggest that the injection with alone LHRH-A2 or hCG or combined LHRH-A2 and hCG fail to increase significantly plasma E2 levels, on the contrary, suppress E2 concentration in female Japanese flounder.5. Conclusion and Suggestion5.1 The gonads of male fish can reach maturation, although that, the injection with LHRH-A2 orhCG fail to stimulate spermiation, the results imply that environmental stress may hinder the spermary development and reproductive progress. The individual fecundity is not going to exert if the stressed male fish is selected to be a candidate spawner. The development process of ovary that is only to stage II is postponed in cultured fish compared with wild Japanese flounder, it is suggested that presence inhibition of gonadal development in cultured fish and lower response of HPG axis to exogenous hormone.5.2 A great deal of GH cells in PPD of the pituitary is consistent with fast growth in culturedfish. A little GtH cells and its granules are consistent with gonadal development and lower response of plasma T and E2 to exogenous hormone. Active ACTH cells in RPD of the pituitary represent a high stress degree in cultured fish. Injections with exogenous hormone fail to stimulate GtH cells and its secretory granules in the pituitary of male and female Japanese flounder.53 Failure of injection with LHRH-A2 or hCG to increase the plasma T and E2 demonstrates that HPG axis has not been started, or the environmental stress damaged highly the endocrinefunction in cultured Japanese flounder.5.4 The endocrine function and its mechanism, the stress of environment and gonadaldevelopment progress in cultured Japanese flounder ought to be researched in future. Method of sustained-release delivery systerm ought to be applied in inducing reproduction progress.