Induction of ovarian development and sex differentiation in the giant freshwater prawn Macrobrachium rosenbergii, by serotonin, methyl farnesoate, and phytoecdysone

Abstract

ABSTRAC          Serotonin (5-HT) and methyl farnesoate (MF) are neurohormones that play important roles in stimulating somatic and gonadal development in decapod crustacea. These agents also accelerate molting that is associated with the reproductive cycle. In addition, ecdysteroids has been reported to regulate molting and concurrent female reproduction, but the stage-specific effects of ecdysteroids on both molting and reproduction during a single molting cycle have not yet been determined for any crustacean. Our study was performed in the giant fresh water prawn, Macrobrachium rosenbergii, after randomly dividing sexually mature female prawns into six groups immediately following ovarian stage I. The groups were: (1) a non-injected normal control group (NC); (2) and (3) control groups injected intramuscularly with crustacean physiological saline (VC1), or CPS plus 5 % ethanol (VC2), respectively; (4) and (5) groups injected with 5-HT or MF at a dose of 0.1 µg/g BW, respectively; and (6) a group injected with phytoecdysone (PE) at a dose of 0.05 µg/g BW. The injections were repeated every five days until spawning. It was found that, the ovarian maturation period (OMP) of the three hormone-treated groups was significantly shortened comparing with the controls. They were 23 + 3.4, 19 + 6.6, and 21 + 10.3 days, respectively, while the OMPs of NC, VC1, VC2 groups were 32 + 3.4, 31 + 3.7, and 31 + 3.7 days, respectively. Average duration of embryonic development period (EDP) from spawn to hatching of each group was not significantly different to the controls. Furthermore, the offspring of the 5-HT- treated group exhibited increased male to female sex ratio at 1.1:1, while MF and PE treated group promote sex ratio at 1:1. These findings demonstrated that, 5-HT, MF and PE could induce ovarian development in giant freshwater prawn, M. rosenbergii. The vitellogenin (Vg) and vitellin (Vt) content during ovarian development in female brood stock during reproductive activity is also discussed.