IRAGO Institute, 377 Ehima-Shinden, Atsumi, Aichi 441-3605, Japan
We sought effective hormonal treatments to induce ovarian maturation and ovulation in the common Japanese conger Conger myriaster by using females cultured for 1.5 years from elver. Effective treatments were human chorionic gonadotropin (HCG; 100IUkg−1 body weight every 2 weeks) in combination with one of three maturation-inducing steroids* (2mgkg−1 body weight). Of these treatments, the combination of HCG and 20β-S seemed to be the most effective. In all fish treated with this combination that survived the experiment, the oocytes developed to the migratory nucleus stage. The survival rate of the HCG-treated females was 79%, and buoyant eggs were obtained from 42% of the females injected with 20β-S. The fertilization rate (no. eggs fertilized/total no. eggs ovulated) was 61%±30%. Furthermore, handling stress seemed to affect the egg quality of C. myriaster, because fertilized eggs were not obtained from females that had been handled more than 12 times.
*Maturation-inducing steroids used: 17α,20β,21-trihydroxy-4-pregnen-3-one (20β-S), 17α,20β-dihydroxy-4-pregnen-3-one (DHP), and 17α-hydroxy-4-pregnen-3,20-dione (17αP).