- The Pacific white shrimp, Litopenaeus vannamei, is a commercially important species in Thailand. One major drawback in the aquaculture of this shrimp is that female broodstocks must have their eyestalks ablated to stimulate ovarian maturation of the ovary. Stimulation by gonadotropin-releasing hormone (GnRH) could conceivably avoid the eyestalk ablation as it could over-ride the inhibition of the gonad-inhibiting hormone (GIH) produced by the eyestalk. In this proposal, we investigated the effects of GnRHs (octopusGnRH (OctGnRH) and lampreyGnRH-III (lGnRH-III), and dopamine on ovarian maturation and spawning, and study of the existence and possible relationship of GnRH and major neurotransmitters in the CNS and ovaries during ovarian maturation in L. vannamei. We found that both GnRH groups showed significantly shortened ovarian maturation period, increased GSI and OD, whereas DA-injected groups exhibited significantly delayed ovarian maturation, decreased GSI and OD, compared with control groups. The numbers of eggs per spawn among experimental groups showed no statistical difference compared with the control group. Both GnRH-irs were more intense in the follicular cells surrounding Oc2 and Oc3. These findings also suggest that GnRHs have a stimulating effect in stimulating ovarian maturation, while DA may play opposite role. Furthermore, we studied the changes in serotonin (5-HT) and dopamine (DA) levels, and their distribution patterns, in regions of the central nervous system (CNS) and ovary, during the ovarian maturation cycle to better understanding about the relationship of neurotransmitters and GnRHs. 5-HT concentration exhibited a gradual increase in the brain and thoracic ganglia, and reaching a maximum at the mature ovarian stage IV. In contrast, DA showed the highest concentration at ovarian stage II in the brain and thoracic ganglia, and then declined to the lowest concentration at ovarian stage IV. In the ovaries, 5-HT was highest at ovarian stage IV, whereas the concentration of DA was highest at ovarian stage II. 5-HT-ir and DAir were distributed extensively in neurons, fibers, and neuropils in the brain, CEG, SEG, thoracic ganglia and abdominal ganglia. In the ovary, 5-HT-ir exhibited high intensity in late oocytes, whereas DA-ir was more intense in early oocytes. This work showed opposing changes in the levels of these two neurotransmitters, and their specific localizations in the CNS and ovary, during ovarian maturation. Overall, this research could provide a useful knowledge for important involvements of GnRH and neurotransmitters in enhancing female white shrimp reproduction.