Aquaculture Breeding Enhancement: Maturation and Spawning in Sea Cucumbers Using a Recombinant Relaxin-Like Gonad-Stimulating Peptide

Wild sea cucumber resources have been rapidly exhausted and therefore there is an urgent need to develop approaches that will help restocking. Currently, there is a lack of information regarding the genes involved in sea cucumber reproductive processes. The neurohormone relaxin-like gonad-stimulating peptide (RGP) has been identified as the active gonad-stimulating peptide in sea stars (Asteroidea), which could also be present in other echinoderm groups. In this study, a sea cucumber RGP was identified and confirmed by phylogenetic analysis. A recombinant <i>Holothuria scabra</i> RGP was produced in the yeast <i>Pichia pastoris</i> and confirmed by mass spectrometry. To assess bioactivity, four levels of purification were tested in an <i>in vitro</i> germinal vesicle breakdown (GVBD) bioassay. The most pure form induced 98.56 ± 1.19% GVBD in <i>H. scabra</i> and 89.57 ± 1.19% GVBD in <i>Holothuria leucospilota</i>. Cruder levels of purification still resulted in some GVBD. Upon single injection into female <i>H. scabra</i>, the recombinant RGP induced head waving behavior followed by spawning within 90-170 min. Spawned oocytes were fertilized successfully, larvae settled and developed into juveniles. Our results provide a key finding for the development of a break-through new artificial breeding approach in sea cucumber aquaculture.