tIn crustaceans, mating occurs during the ecdysis after female molting. During this period,a male transfers its spermatophore into a female which, in some species, stores the sper-matophore for a long period prior to spawning and fertilization. However, in some speciesincluding the giant freshwater prawn, Macrobrachium rosenbergii, the male deposits itsspermataphore onto the external surface of the thoracic segment of the female which affectsthe spawning time and maternal behavior. This study investigated the spawning behaviorof the M. rosenbergii females, which was divided into pre-spawning, spawning, and post-spawning phases. It was revealed that mated female prawns with attached spermatophoreexhibited an earlier spawning than unmated individuals, leading to assessment of the fac-tors that may elicit this phenomenon. Four groups of female prawns were allocated togroups including mating females with spermatophore still attached, mating females withthe spermatophore removed, artificially inseminated females with spermatophores, andan unmated control. There was a significant reduction in the time of egg-spawning in thepresence of spermatophores, and the mating activity was also a contributing factor. Further-more, over 90% of the mated and artificially inseminated females in which spermatophoreswere deposited carried the eggs in the abdominal brood chamber until completion ofembryonic development while others discarded the eggs within 2 days post-spawning.This study implies that the spermatophore may contain ovulation-inducing factors whichstimulate an earlier spawning and fostering of brooding behavior.