FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

Pond-reared female Japanese eel Anguilla japonica, (n=210) with a mean total length of 83.2±6.3 cm (67.5-103.5 cm) and body weight of 1072±191 g (623-1700 g) were used for induction of maturation. The maturity of females was divided into 6 classes (classes 0-5) based on the black coloration of the pectoral fins. Females were injected with 0.5 or 1 IU/g BW of human chorionic gonadotropin (HCG) at 2 weeks interval in the first month in order to synchronize their maturity up to grades 3-4 one month after hormonal treatment. Subsequently, female with body weight over 800 g were injected with a dosage of 4 catfish pituitary homogenate, and 3 catfish pituitary homogenate for those with the body weight below 800 g. Accompanied with shortening of the injection interval, and reduction of injection dosage at the late stage of induction, final maturation can be attained in 2 months after hormonal treatment. Ovulation was induced by treatment of 17 , 20  - dihydroxy – 4 - pregnen-3-one (DHP, 2 g/g BW). Spawning was found occasionally in 100 L aquarium by mating with 3 - 5 males per fem ale. The goal of producing fertilized eggs all year around can be achieved by inducing the female broodstock to spawn in aquaria using DHP injection, with or without stripping 15-16 h after treatment. The onset of maturation in eel can be enhanced by treatment of HCG, and treatment of HCG together with catfish pituitary homogenate synergistically reduced the induction period. However, only 44.8 % of pond-reared female attained the final maturation. About 70% among matured female attained the final maturation stage within 2 - 4 months after hormonal treatment. The minimum size of female for successful spawning and producing the larvae until the feeding stage is 623 g. The induction period of females to produce viable feeding larvae ranged between 61 and 175 days. Asynchronization of oocyte development and difficulty in time decision for inducing ovulation based on body weight index (BWI) are the main problems of induction maturation in female eels, because the lower BWI was found in the female with long period treatment. For male, the spermatogenesis was induced by treatment of 1-2 IU/g BW HCG per 1 - 2 weeks interval in accordance with to the maturity status of female.
Key words: Anguilla japonica, Induced maturation, Human chorionic gonadotropin (HCG), 17, 20-dihydroxy-4-pregnen-3-one (DHP)