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

Abstract

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.