Abstract

Oogenesis and ovarian development in female Panulirus japonicus were examined by light and electron microscopy. Eight substages (oogonium, bouquet, chromatin nucleolus, oil globule, pre-yolk platelet, yolk platelet, pre-maturation and maturation) were distinguished in the typical process of oogenesis (multiplication, pre-vitellogenesis, vitellogenesis and maturation stages). Yolk accumulation started at the late pre-yolk platelet substage, when electron-dense granules appeared. Yolk granules seemed to be accumulated in two ways, being produced endogenously by the abundant rough endoplasmic reticulum during vitellogenesis and exogenously by micropinocytosis from the yolk platelet to pre-maturation substages. Ovulation occurred after oocytes became mature (i.e. after the metaphase of the primary maturation division was reached). The diameter of mature oocytes was 465–477 µm.

The seasonal ovarian development cycle was divided into seven stages: inactive, developing, ripe, re- developing, re-ripe, spawned and recovery. The morphological characteristics relating to the gonadosomatic index (GSI) of each stage are described (GSI was calculated by the formula I = W × 10⁵/L³, where I represents GSI, W is the gonad weight in grams, and L is the carapace length in millimetres). Estimated GSI values ranged from 11.3 to 12.4 in individuals with mature oocytes, and the 99% confidence intervals for GSI values of adjacent oogenesis substages did not overlap. GSI values at the developing and ripe stages were significantly larger than those at the re-developing and re-ripe stages, respectively.