1IRAGO Institute, Tahara, Aichi 441-3605, 2Ocean Research Institute, The University of Tokyo, Nakano, Tokyo 164-0014, Japan
To improve techniques for artificial seed production of the Japanese eel Anguilla japonica, we evaluated two types of artificial fertilization methods: i) the spontaneous spawning method of paired specimens and ii) the stripping-insemination method, by comparing the quality of eggs and larvae obtained. Females artificially matured by the injection of salmon pituitary extract were kept at 20°C before final treatment with 17α,20β-dihydroxy-4-pregnen-3-one. Afterwards, each female for i) the spontaneous spawning method was kept in an individual tank with three males and water temperature was raised to 22°C. For ii) the stripping-insemination method, ovulated fish kept at 20°C for about 15 hrs were stripped and eggs obtained were inseminated. Eggs and larvae obtained by i) the spontaneous spawning method (n＝12) showed significantly higher fertility (80±14%), hatching rate (62±23%), survival rate at 5 days after hatching (54±22%), and lower deformity at 5 days after hatching (60±23%) than those obtained by ii) the stripping-insemination method (n＝14, 41±32%, 31±29%, 27±25%, 79±19%, respectively). These results show that the spontaneous spawning method at 22°C is better than the stripping-insemination method at 20°C for the fish quality in artificial eel seed production.