白斑狗鱼雌性化诱导和雌雄同体现象

Feminization induction and hermaphroditism of northern pike(Esox lucius)

为研究和开发白斑狗鱼雌性化诱导方法,实验将750尾白斑狗鱼仔鱼随机分为5组,其中4组为实验组,分别从不同的发育时间(孵出后第10、20、30和40天)开始投喂用20 mg/L雌二醇浸泡过的水蚯蚓,另外1组为空白对照组,投喂正常水蚯蚓。各实验组喂饲17β-雌二醇30 d,然后将实验组和对照组的所有鱼进行正常饲养。至206 d将实验组和对照组的鱼进行成活情况统计,然后分别进行解剖,取出性腺进行组织学观察。结果显示,投喂用20 mg/L雌二醇浸泡过的水蚯蚓对白斑狗鱼仔鱼具有非常明显的致死效应,成活率由对照组的43.5%下降到14.3%±8.3%;30 d喂药组和40 d喂药组获得较高的雌雄比例,特别是30 d喂药组最高,达到了15∶7,由此推断白斑狗鱼性腺分化的关键时间点可能在孵出后的30~40 d;各实验组和对照组都出现很高比例的雌雄同体现象,即在同一性腺中同时出现了大量的初级卵母细胞(第Ⅱ时相)和精母细胞,而且这些卵母细胞有明显的退化现象,推测其性别分化过程中存在雌性先熟的幼体雌雄同体现象。本研究将为采用激素诱导手段生产白斑狗鱼全雌化苗种以及探讨白斑狗鱼性别决定和分化机制提供依据。

Northern pike（Esox lucius） is a very popular edible fish with high quality and an economically important fish. In China, northern pik is only distributed in the Ertixche River in northern Xinjiang. Northern pike females grow faster than males. To investigate and develop the feminization induction method on northern pike, 750 fries of this fish were divided into five groups in this study. Among them, four groups were used as experimental groups, and fed with Tubifex hattai, which had been soaked with 20 mg/L 17β-estradiol, starting from different developmental time（10 d, 20 d, 30 d and 40 d, respectively after hatching）. The other one group was used as control group, and fed with normal T. hattai. All fish in experimental groups were fed with 17β-estradiol for 30 d, and then all the fish in the experimental groups and the control group were fed normally. On 206 d, survival situations of the fish in all groups were counted, and then all the fish were dissected, gonads were removed to perform histological observation. The results showed that feeding with T. hattai, which had been soaked with 20 mg/L 17β-estradiol,had very obvious lethal effect on northern pike fries, and made the survival rate decreased from 43.5% in the control group to 14.3%±8.3%. Higher ratios of female to male were obtained in 30 d treated group and 40 d treated group, especially the highest ratio, which reached 15∶7, was obtained in the 30 d treated group, so it can be concluded that the key time point of gonad differentiation of northern pike may be in the period of 30–40 d after hatching. There were high proportions of hermaphroditism in both experimental and control groups, that is, a large number of primary oocytes（phase II） and spermatocytes appeared simultaneously in the same gland, and moreover, these oocytes showed marked degeneration. It is presumed that there was a protogynous juvenile hermaphroditism in the process of sexual differentiation of northern pike. This study will provide certain basis for production of all female northern pike fries using hormone induction techniques and further research on sex determining mechanism of northern pike.