Abstract
Gonad and blood samples were taken from the cultured female Korean sea bass, Lateolabrax japonicus from October to February between 1997 and 1999. Gonadosomatic index began to increase in November and reached the highest value in December (12.8$\pm$1.5) and January (14.8$\pm$3.5), and then decreased sharply in February (2.6$\pm$1.5, p<0.05). The ovarian oocytes developed to tertiary yolk stage and reached fully-Brown stage in December and January, and then underwent atresia without maturation and ovulation in February. The plasma estradio3-17 $\beta$ level increased from November, and reached the highest value in December (1,152.3$\pm$107.2 pg/ml) and January (1,315.4$\pm$99.5 pg/ml), after then decreased in February (P<0.05). The concentration of plasma 17 $\alpha$ ,20 $\beta$-dihydroxy-4-pregnen-3-one was not significantly changed at low levels (86.6$\pm$6.5∼93.8$\pm$2.8 pg/ml) during the experimental period (P<0.05). All the fish with fully-grown oocytes in the ovary were matured and ovulated by HCG injection. The number of floating eggs were 325,000$\pm$26,000 at HCG 1,000 luhg and 195,000$\pm$35,000 at 2,000 lUikg. There was no difference in fertilization rate and hatching rate of the eggs (P<0.05). Considering these results, we could infer that the ovarian oocyte of the cultured Korean sea bass were not matured and ovulated because of the lack of gonadotropin surge. Moreover, HCG injection could induce oocyte maturation and ovulation in the cultured fish, and the effective dose was 1,000 IU/kg.
양식산 농어, Lateolabrax japonius 암컷의 난소와 혈액을 1997년부터 1999년까지 매년 10월부터 2월까지 2회 반복 채취하였다. Gonadosomatic index는 11월부터 증가하기 시작하여 12월(12.8$\pm$1.5)과 1월(14.8$\pm$3.5)에 최고 수준을 나타낸 후 2월(2.6$\pm$1.5)에는 급격히 감소하였다(P<0.05). 난소내 난모세포는 12월과 1월에 3차 난황구기까지 발달하고 성장이 완료되지만, 성숙 및 배란이 되지 않고 2월에는 퇴화되었다. 혈중 estradiol-l7$\beta$의 농도는 11월부터 증가하기 시작하여 12월 (1,152.3$\pm$107.2 pg/ml)과 1월(1,315.4$\pm$99.5 pg/ml)에 최고 수준을 나타낸 후 2월에는 급격히 감소하였다(P<0.05). 17 $\alpha$,20-dihydroxy-4-pregnen-3-one는 실험기간 동안 낮은 농도(86.6$\pm$6.5~93.8$\pm$2.8 pg/ml)를 유지하며 유의한 변화는 없었다(P<0.05). 성장이 완료된 난모세포를 갖고 있는 양식산 농어에 HCG를 주사(1,000 IU/kg과 2,000 IU/kg)하면 모든 개체에서 성숙 및 배란이 유도되었다. HCG 농도에 따른 수정율과 부화율은 차이가 없었으나, 부상란 수는 1,000 lU/kg에서 325,000$\pm$26,000개, 2,000 IU/kg에서 195,000$\pm$35,000개로 차이가 있었다. 이상의 결과를 종합하면, 양식산 농어 암컷은 양식환경 하에서도 난황형성 및 난모세포의 성장은 정상적으로 진행되지만, gonadotropin의 surge가 일어나지 않아 최종성숙과 배란이 되지 않는 것으로 추정되었다. 농어에서 난모세포의 인위적 성숙 및 배란 유도에 의한 난 생산은 HCG 1000 IU/kg가 효과적이었다.