人工誘導日本鰻自然產卵排精之研究

Abstract

良好種鰻之育成，可提高人工誘導養殖鰻的自然產卵排精率，育成品質之檢視及改善自不可免，包括誘導時銀化是否有進展及雄魚是否可誘導成熟，與誘導前雌鰻卵細胞發育情形。而為能簡化及整合誘導技術，本研究雌雄鰻皆使用相同之兩階段誘導法誘導，以期能誘導成熟，及雌雄鰻能配合 timing 達到同步自然產卵排精。 本研究採用上市的養殖成鰻，平均體重為 564 ± 102 公克，經海水馴化兩週，於第一階段誘導後，結果發現，種鰻在淡水中激素誘導生殖腺發育，銀化程度無明顯進展，而海水中不論是否經激素誘導生殖腺發育，銀化程度皆有明顯進展，銀化程度與降海野生鰻幾無差異。人工誘導前，雌鰻部份卵細胞發育到表層泡期，已可達到內生性卵黃生成時期。經十至十二週的激素誘導，雄鰻 70 ％可達精子成熟階段，精細管管腔中充滿大量成熟精子，雄鰻精子成熟所需誘導時間較雌鰻成熟排卵約晚二週。雌鰻經第一階段 salmon pituitary homogenate ( SPH ）併用 17α- methyltesto - sterone ( MT ）誘導，其卵巢內卵細胞可達同步發育階段，第二階段催熟以 SPH 併用 1 7α- hydroxyprogesterone ( OHP ) ，全程使用外源性 SPH ，可進一步改善雌鰻無法一次產卵之缺點。成熟種鰻經第二階段催熟後移入 14 噸大水池中，雌雄鰻的 timing 可同時配合，皆在19小時開始自然產卵排精，受精率約60-85 % ，在水溫 22－23℃ 下，受精卵約經 38 小時孵化。因此本研究改進之兩階段誘導法，可同時適用於誘導雌雄鰻發育成熟，種鰻無需事前之分別育成，經誘導成熟之雌雄鰻可經第二階段同步催熟達自然產卵排精，可一次收集大量孵化幼苗，供復續培育研究所需。

As the quality of mature spawners can affect the success in the synchronous spawning and spermiation, the evaluation of the spawners’ characters becomes prerequisite. In addition to evaluation the extent of gonad maturation of both genders, the advancement of silvering-related changes of the eels under seawater condition was also critically examined. This study aims to follow the same two-step strategy to induce both genders of immature Japanese eels (Anguilla japonica) to fertilize under artificial condition. The cultured Japanese eels with body weight of 564±102g, were acclimated to seawater for two weeks. Prior to induction, the extent of ovarian growth had attained the cortical alveolar stage of previtellogenesis. Without hormonal induction, the silvering-related changes also advanced after 6 weeks in the seawater. On the contrary, with or without hormonal induction, silvering-related changes did not advance in the fresh water. Therefore, after the first-step induction in the seawater, the silvering-related changes advanced prominently in association with the gonad maturation. The extent of silvering is comparable to the wild migratory ones in fresh water. In the first-step induction, weekly injections of salmon pituitary homogenate (SPH) plus methyl testosterone (MT) were adopted for 6 weeks, and thereafter, replaced by only SPH until the completion of vitellogenesis or spermatogenesis. The SPH plus 17α-hydroxyprogester- one(OHP) were then adopted further for the second-step induction. The spermiation peak lagged behind the vitellogenesis peak for about two weeks. Two thirds of males spermiated for two to four weeks of duration. Intraovarian oocytes could be induced to mature synchronously by SPH plus MT in the first-step. SPH must be adopted throughout in the process of induction because the supplement of SPH to OHP in the second-step improved the occurrence of spontaneous spawning in the females. Further, the synchronous spawning and spermiation was observed in 14 tons pool, timely on the 19th hour after final induction. The fertilization rate was about 60-85% and the eggs hatched at the 38th hour under 22-23°C water temperature. As results, this modified two-step method can be applied to induce maturation of both genders initially from immature status of gonad to spontaneous spawning and spermiation. This simplifies and integrates the induction technigue of the eels.