IRAGO Institute, Atsumi, Aichi 441-3605, Japan
Artificial induction of ovarian maturation and ovulation of the common Japanese conger Conger myriaster was achieved in 1998 and 1999. Elvers of common Japanese conger caught in Mikawa bay, central Japan, in autumn in 1996 and 1997 were reared in sea water ponds for one and a half years to adult. Almost all of fish over 250g in body weight (BW) were female and possessed oocytes at the secondary yolk globule stage at the start of the experiment. A total of 48 females were injected with human chorionic gonadotropin (HCG) at a dosage of 100IU/kgBW every two weeks in seawater at about 10°C. After 5 to 10 times of HCG injection, their oocytes developed to the migratory nucleus stage. To induce final oocyte maturation and ovulation 14 females were injected with 17α, 20β, 21-trihydroxy-4-pregnen-3-one at a dosage of 2mg/kgBW. Thereafter 12 of them ovulated. Ovulated eggs were pelagic type possessing 10 to 20 oil droplets and 874 to 1126μm in diameter. Fertile eggs were obtained from one female and their average diameter was 1010±37μm.