抄録
Maturation of female Japanese mitten crabs Eriocheir japonica (De Haan, 1835) was observed and the relationship between maturity and reproductive ecology investigated. The degree of maturity was indicated by juvenile and adult phases from their exoskeleton, gonad index (GI), six developmental stages of oocyte from histological observation, oocyte diameter, and four developmental stages of embryos. The stages of most advanced oocytes were used for assessing ovarian maturity. During the juvenile stage the ovary proceeds to previtellogenesis and primary vitellogenesis but remains immature (at most stage 2, GI < 1.0, oocytes < 100μm diameter). After the pubertal moult, oocytes begin secondary vitellogenesis, and complete development (stages 2-6, GI 0.28-13.2, 120-400μm diameter). The number of developing oocytes varied from ca. 120,000 (40mm at carapace width) to 650,000 (70mm). Copulation is estimated to be possible only when adult females complete vitellogenesis. After oviposition, underdeveloped oocytes start secondary vitellogenesis with the development of embryos, and are spawned as the second or third broods after fertilization by stocked sperm without ecdysis. Most of the developing oocytes are spawned at each oviposition, and unspawned matured oocytes are considered to be digested and absorbed.
