ブリ

Induction of oocyte maturation and ovulation in Japanese yellowtail Seriola quinqueradiataa is necessary for mass production of early juvenile used for sea-farming. Higher water temperature (19℃) and long photoperiod (16L:8D) enhanced the earlier growth of gonads. After confirming the yolk accumulation by monitoring egg diameter through ovarian biopsy, three different ways of hormonal treatment were applied to induce oocyte maturamation and ovulation in cultured four-year-old female fish. Egg quality, represented by the fertilization rate and hatching rate, in the first experimental group (single injection of HCG (500 IU/kg)) showed the highest values among three different hormonal treatments. Moreover, in this group ovulation occurred at around 48 hours after the HCG injection. In the second experimental group (priming injection of HCG (100 or 50 IU/kg)+one day after HCG injection (500 IU/kg)), the largest quantity of ovulated eggs per fish was obtained, however, the egg quality was lowest among the three groups. Quality of the eggs from the third experimental group (single implantation of LHRHa cholesterol pellet, LHRHa 200 or 400 μg/kg) was relatively high, but egg number per fish showed the lowest level. Therefore, it is concluded that a single injection of HCG is the most simple and efficient method to induce oocyte maturation and ovulation for obtaining a large quantity of fertilized eggs with good cluality in the cultured yellowtail.