Artificial induction of ovarian maturation and ovulation in the common Japanese conger Conger myriaster

Artificial induction of ovarian maturation and ovulation of the common Japa nese conger Conger myriaster was achieved in 1998 and 1999. Elvers of commo n Japanese conger caught in Mikawa bay, central Japan, in autumn in 1996 an d 1997 were reared in sea water ponds for one and a half years to adult. Al most all of fish over 250 g in body weight (BW) were female and possessed o ocytes 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 100 IU/kgBW every two weeks in seawater at about 10 degrees C. After 5 to 10 times of HCG injection, their oocytes developed to the mig ratory nucleus stage. To induce final oocyte maturation and ovulation 14 fe males were injected with 17 alpha, 20 beta, 21-trihydroxy-4-pregnen-3-one a t a dosage of 2 mg/kgBW. Thereafter 12 of them ovulated. Ovulated eggs were pelagic type possessing 10 to 20 oil droplets and 874 to 1126 mum in diame ter. Fertile eggs were obtained from one female and their average diameter was 1010 +/- 37 mum.