Gonadotropin-releasing hormone (GnRH) and a GnRH analog induce ovarian maturation in the giant freshwater prawn, Macrobrachium rosenbergii

Abstract

Gonadotropin-releasing hormone (GnRH) is a highly conserved peptide that plays a role in regulating reproduction in both vertebrates and invertebrates. The present study investigated the effects of lamprey (l)GnRH-I, lGnRH-III, octopus (oct)GnRH and buserelin, a GnRH analog (GnRHa), on ovarian maturation and spawning in the giant freshwater prawn, Macrobrachium rosenbergii. We demonstrated that the times for ovarian maturation in prawns treated with octGnRH (at 50 and 500 ng/g BW), lGnRH-I and lGnRH-III (at 500 ng/g BW), and GnRHa (at 1,000 ng/g BW) were significantly shorter (23.50 ± 2.12 and 22.50 ± 1.15, 25.50 ± 4.04 and 25.50± 4.03, and 26.67 ± 4.04 days) than the controls (40.0 ± 3.40 days). On day 22 post-treatment, the gonadosomatic index (GSI) values of the prawns treated with octGnRH (at 50 and 500 ng/g BW), lGnRH-I and lGnRH-III (at 500 ng/g BW), and GnRHa (at 1,000 ng/g BW) were significantly greater (2.50 ± 0.72 and 4.64 ± 0.95, 6.07 ± 1.29 and 8.90 ± 1.04, and 3.88 ± 1.34%) than the controls (0.45 ± 0.15%). Vitellin protein was first detected in the ovary on day 15 and had increased significantly by day 22 in prawns treated with GnRHs at 500 ng/g BW, while it was not detected in the controls. The prawns treated with the GnRHs and GnRHa showed similar numbers and percentages of spawned and fertilized eggs to those of the control group. These findings indicate that GnRH controls ovarian maturation and spawning in this prawn, as in other species.