| Summary: | 碩士 === 國立臺灣大學 === 漁業科學研究所 === 89 === The cultivated Japanese eel (Anguilla japonica) is usually immature in reproduction, it cannot proceed to accomplish final maturation without first inducing the vitellogenesis. Artificial induction of maturation in Japanese eel has been performed by serial injections of Salmon Pituitary Homogenate (SPH) and DHP, yet still not so effectively. The induction rate of vitellogenesis is not more than 50% by SPH treatment, and eggs with good quality cannot always be spontaneously obtained finally by DHP treatment. Therefore, this experiment was designed to follow Wang (1999), using SPH cotreated with exogenous steroids to improve the induction rate of
vitellogenesis, then induced eels to the final maturation.
The Japanese eel (504±84 grams) were tagged and separated into three groups randomly: SPH treatment, and SPH cotreated with MT (for 6 weeks only, or weekly injection). The injections were performed once a week to induce vitellogenesis. In addition to in vivo study, this study also examined the effect of DHP and OHP in final maturation in vitro. Result showed that SPH cotreated with MT for 6 weeks could induce more eels to start vitellogenesis than those of SPH alone after 7~8 weeks of the treatments. However, the existence of MT during late vitellogenesis stage would delay but cannot inhibit the hydration to occur. The eels with hydrated oocytes can proceed with induction of final maturation by DHP or OHP. In morphology examination, the intra-ovarian oocytes were transparent and with oil droplets centrally located under a binocular microscope. It was suitable for those oocytes to proceed
with induction of final maturation.
All of the eels with hydrated oocytes could be induced to GVBD and ovulate at 14~20 hrs after DHP or OHP injection. The eels oviposied at 2~7 hrs after ovulation induced by DHP. In contrast, the eels oviposited within 4 hrs after ovulation by OHP. As the quality of eggs retained in body cavity decreased rapidly after ovulation. The time interval between ovulation and oviposition in OHP group were obviously shorter than in DHP group. Therefore, better eggs can be obtained if the spawner is
induced to oviposite spontaneously by OHP.
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