Abalone egg-laying hormone induces rapid ovarian maturation and early spawning of the giant freshwater prawn, Macrobrachium rosenbergii

Egg-laying hormone (ELH) is a peptide hormone that is involved in spawning and egg-laying behaviors in many mollusks. The present study demonstrated the presence of an ELH-like hormone in the ovary of the freshwater prawn, Macrobrachium rosenbergii, using a polyclonal antibody against abalone ELH (aELH). The immunoreactivity against aELH (aELH-ir) was detected in follicular cell type 2 (Fc2) of stages 0 to III ovaries, and in the cytoplasm of mature oocytes of stage IV ovaries. In contrast, there was no aELH-ir detected in the central nervous system (CNS). The effect of aELH on reproductive processes in this species was determined by in vivo bioassays, using intramuscular (i.m.) injections. The gonadosomatic index (GSI) values of control prawns at 15 days post-treatment was 0.5 ± 0.1% (X̅ ± S.D.), but 5.8 ± 0.6% when treated with 50 ng/g BW of aELH, and 5.4 ± 1.1% with a 500 ng/g BW dose. The time for ovarian maturation and spawning of the control group was 40.0 ± 3.4 days, but only 22.0 ± 2.4 days following injections with 50 ng/g BW of aELH, and 21.2 ± 2.8 days with a 500 ng/g BW dose. However, there were no differences in the number of eggs spawned and fertilization rates after aELH treatments. These findings support the hypothesis that an ELH-like hormone is present in M. rosenbergii, and could have a significant role in female spawning.