Ovarian re-maturation following the first spawning in the Chinese mitten crab, Eriocheir sinensis (H. Milne-Edwards)

Abstract

The present study investigated the external and histological changes in the ovary and measured the gonadosomatic index (GSI) and hepatosomatic index (HSI) during the re-maturation of the Chinese mitten crab Eriocheir sinensis. The results show that the ovarian re-maturation cycle of this crab species can be divided into four stages, i.e. Stage I: the ovary had an X shape and appeared milky white or with a mottled buff colour, and the dominant gametocyte at the stage were oogonia (OG, 28.3%) and previtellogenic oocytes (PR, 31.6%); Stage II: the ovary appeared light yellow or tan in colour, dominated by endogenous vitellogeic oocytes (EN, 69.3%). The yolk globules of unreleased mature oocytes (MO) from the previous spawn were absorbed, leaving many vacuoles in the retrogressing MO; Stage III: the ovary appeared crimson red or deep purple, and although the main type of gametocyte was exogenous vitellogenic oocytes (EX), near-mature oocytes (NO) could also be found in the late phase of the ovarian development stage; Stage IV: the ovary was ripe and filled with MO that contained large yolk globules. During the period of the second ovarian maturation cycle, the GSI increased significantly from the time just after the first spawning (P<0.01). However, although HSI appeared to decrease within days after spawning (DAS), no significant correlation was found between GSI and HSI or between HSI and DAS (P>0.05). Furthermore, the final GSI and the volume of MO of E. sinensis during the second maturation cycle were drastically lower than those of the first maturation cycle.