Hemolymph vitellogenin levels and ovarian development during the reproductive and non-reproductive molt cycles in the giant freshwater prawn Macrobrachium rosenbergii

Abstract

In this study, ovarian development and vitellogenin levels were determined during the reproductive and non-reproductive molt cycles in the giant freshwater prawn Macrobrachium rosenbergii in order to examine the relationship between vitellogenesis and molting. During the reproductive molt cycle, the ovary developed synchronously with the advancement of molting stage. At molting stages B-C0, the ovaries contained oogonia and oocytes at the previtellogenic and endogenous vitellogenic stages, and hemolymph vitellogenin levels were relatively low (2.4-3.0 mg/mL). At stage C1, yolk accumulation commenced in oocytes at the endogenous vitellogenic stage, after which oocytes entered the exogenous vitellogenic stage. Vitellogenin levels increased (4.9 mg/mL) at this stage. During premolt stages D0-D3, vitellogenin titers were high (4.7-7.3 mg/mL), and gonadosomatic index (GSI) increased rapidly due to the yolk accumulation in the oocytes. Following ecdysis, yolk accumulation was completed at stage A0, and oviposition occurred. Entering stage A, vitellogenin levels became low (0.6-1.3 mg/mL). In contrast, throughout the non-reproductive molt cycle, GSI remained low, and oocytes did not develop beyond the previtellogenic or endogenous vitellogenic stage. Some atretic oocytes at the exogenous vitellogenic stage were observed in a few females. During the non-reproductive molt cycle, vitellogenin levels did not show distinct changes in relation to the molt cycle.