In Vitro Hatching of Scylla paramamosain Embryos: Insights from Developmental and Transcriptomic Analyses

Scylla paramamosain is a commercially important crab species widely cultured in China. However, artificial breeding remains limited by the high mortality of ovigerous females and asynchronous embryo hatching. In vitro embryo hatching has emerged as a promising alternative, yet its practical feasibility and underlying molecular mechanisms have not been systematically investigated. In this study, we examined the developmental characteristics of S. paramamosain embryos under different temperature regimes and hatching modes, evaluated embryo viability following maternal death, and compared transcriptomic profiles of Zoea I larvae between in vitro and maternal hatching. Our results demonstrated that temperature had a pronounced effect on embryogenesis and survival, with 27-30 °C identified as the optimal range for development and hatching. Both low and high temperature extremes markedly reduced embryo survival. Developmental trajectories were largely comparable between in vitro and maternal hatching, confirming the reliability and feasibility of the in vitro approach. Embryos collected within 4 h after maternal death exhibited high hatching success, whereas those obtained after 8 h failed to hatch. Transcriptomic analysis revealed 3505 differentially expressed genes, including 1933 upregulated and 1572 downregulated, which were significantly enriched in pathways related to cell cycle regulation, energy metabolism, immune defense, and ion transport. These findings implied that in vitro embryos could maintain developmental competence by stabilizing genomic integrity, reallocating energy resources, and activating stress responsive mechanisms. This study provides the first comprehensive evidence supporting the feasibility of in vitro embryo hatching in S. paramamosain and offers practical insights for optimizing temperature regimes, improving the utilization of maternal resources, and advancing large scale seedstock production in crab aquaculture.