| Budget Amount *help |
¥2,700,000 (Direct Cost: ¥2,700,000)
Fiscal Year 1998: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1997: ¥1,900,000 (Direct Cost: ¥1,900,000)
|
|---|
| Research Abstract |
Much information on the mechanisms of gonadal maturation in teleosts has been collected using single spawning species, such as salmonids, as a model. In this study the rose bitterling Rhodeus ocellatus ocellatus, a multiple spawning cyprinid was used as a model for multiple spawners.
1. changes in fine structure of gonadotrophs during short reproductive cycle : Short reproductive cycle of the bitterling was divided into three phases ; pre-ovulation, ovulation, and post-spawning. Only one type of gonadotroph was observed in the proximal pars distalis of the pituitary. Throughout the cycle, the size and number of small granules did not change significantly.However, the size of large globules (LG) changed drastically ; the diameter of LG was 13000-15000* in the pre-ovulation phase, then it increased to 15000-28000* in the spawning phase, and decreased to7500-12500* in the post-spawning pahse.
2. In vitro steroid production in the ovary during short reproducitve cycle : Yolk accumulated oocytes were divided into two groups ; pre-ovulating large oocytes (LO, longer diameter 1.2-1.7 mm) and small oocytes (SO, 0.6-1.1 mm) .LO or SO were incubated with or without salmon pituitary extract (SPE ; 10 or 100 mug/ml) or pregnant mare serum gonadotropin (PMSG ; 10 or 100 IU/ml) . In the post-spawning fish, both LO and SO produced almost the same amount of estradiol 17beta(E2 ; yolk production stimulating steroid) and 17, 20beta-dihydroxy-4-pregnen-3-one (17, 20fbeta- P ; oocyte maturation inducing steoid) in accordance with the administration of external gonadotropin. In the pre-ovulation fish, however, the production of E2 was much higher in SO than that in LO.In contrast, LO produced large amount of 17, 2Obeta-P compared to that produced by SO in response to gonadotropin administration.
|
