Mechanisms of multiple spawning of teleosts

许多关于硬骨鱼性腺成熟机制的信息都是以单一产卵物种，如鲑鱼为模型收集的。在这项研究中，多产卵的鲤科鱼类--玫瑰苦鱼Rhodeus ocellatus ocellatus被用作多产卵的模型。短生殖周期中促性腺激素细胞超微结构的变化：苦鱼的短生殖周期分为排卵前、排卵和产卵后三个阶段。只有一种类型的促性腺激素出现在垂体腺的近端和远侧部。在整个周期中，小颗粒的大小和数量变化不大，但大颗粒的大小变化很大，排卵前期大颗粒的直径为13000~15000*，产卵期增大到15000~28000*，产卵后减小到7500~12500*。短生殖周期内卵巢的体外类固醇分泌：将卵黄积聚的卵母细胞分为两组：排卵前的大卵母细胞(直径1.2~1.7 mm)和小卵母细胞(直径0.6~1.1 mm)，分别与或不加鲑鱼脑垂体提取物(SPE；10或100µg/ml)或孕马血清促性腺激素(PMSG；10或100 IU/ml)孵育。在产卵后的鱼中，根据外源促性腺激素的作用，LO和SO产生几乎相同数量的17β雌二醇(E_2；促卵黄生成类固醇)和17，20β-二羟基-4-孕烯-3-酮(17，20f-P；卵母细胞成熟诱导类固醇)。然而，在排卵前的鱼中，SO产生的E_2远远高于LO。相反，LO产生大量的17，20β-P，而SO对促性腺激素的反应是产生大量的17，20β-P。

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.