1Kanagawa Prefectural Fisheries Research Institute, Miura, Kanagawa 238-0237, 2Japan NUS Co., Ltd., Tokyo 108-0022, Japan
The maturation process of female alfonsino Beryx splendens in the spawning season was studied by histological examination and gonad index (GI). A total of 281 specimens were collected in the fishery grounds around Izu Islands from July to August in 1993. Ovarian development of the fish ranging from 23.3 to 49.0 cm in fork length (FL) was divided into 7 stages, where GI was regarded as a good marker for sexual maturation. The minimum size for maturation and the size at which 50% of the population attained sexual maturity (FL50) were 31.8 cm and 32.5 cm, respectively. The specimens collected off Izu Peninsula in July showed advanced maturity compared with those collected off Hachijo Island. The results suggested that alfonsino in water around Izu Islands have different maturation rate depending on the sea area.