Effects of gonadotropin-releasing hormones and dopamine on ovarian maturation in the Pacific white shrimp, Litopenaeus vannamei, and their presence in the ovary during ovarian development

We investigated the effects of two isoforms of gonadotropin-releasing hormone (GnRH), namely octopus GnRH (octGnRH) and lamprey GnRH-III (IGnRH-III), and a neurotransmitter, dopamine (DA), on ovarian maturation and spawning in the Pacific white shrimp, Litopenaeus vannamei. The effects of GnRHs and DA were examined by evaluating gonadosomatic indices (GSIs), oocyte diameters (ODs), proliferation of the germ cells, and hemolymph vitellogenin (Vg) concentrations. Both GnRH groups at the doses of 25 and 250 nglg BW showed significantly shortened ovarian maturation period, increased GSI and OD, whereas DA-injected groups at doses of 2.5 x 10(-7) and 2.5 x 10(-6) mol/shrimp showed significantly delayed ovarian maturation, decreased GSI and OD, compared with control groups. However, the numbers of eggs per spawn among experimental groups showed no statistical difference compared with the control group. Injecting GnRHs into shrimps significantly increased hemolymph Vg concentrations at ovarian stage IV compared with the control group, whereas injecting DA had the opposite effect. PCNA staining was detected in oogonia and pre-vitellogenic oocytes in both groups of GnRHs, and showed significant increases of cell proliferation, at day 14, compared with the control groups. In contrast, the groups injected with DA showed statistical decrease of cell proliferation at the same clay. GnRH-immunoreactivities (-irs) and DA-ir were both detected in the ovaries. Both GnRH-irs were more intense in the follicular cells surrounding Oc2 and Oc3, whereas DA-ir was intense in the early steps of oocytes. These findings suggest that GnRHs have a stimulating effect on ovarian maturation, while DA may play an opposite role. This study could provide a useful knowledge for enhancing female white shrimp reproduction. (C) 2013 Elsevier B.V. All rights resented,