Application and Effects of GDF9 as a Novel Inductive Additive on Early Ovarian Development in Japanese Eel (Anguilla...

Anguilla japonica (Japanese eel) is a commercially valuable aquaculture species, yet large-scale artificial reproduction remains a major unresolved challenge. This study evaluated the potential of growth differentiation factor 9 (GDF9), an oocyte-derived regulator, as a supplementary additive during hormonally induced ovarian development in Japanese eel. Compared with treatment using gonadotropin analogs alone, co-administration of exogenous recombinant GDF9 significantly enhanced early ovarian development, as indicated by an increased gonadosomatic index (GSI), improved follicular growth, and elevated serum estradiol (E2) and vitellogenin (VTG) levels. Transcriptomic analysis showed that differentially expressed genes (DEGs) were significantly enriched in biological processes and pathways related to EGF signaling, angiogenesis, cell proliferation, transmembrane transport, and reproductive signaling, including the GnRH, FoxO, and Apelin pathways. Metabolomic profiling further revealed significant changes in metabolites associated with carbohydrate metabolism, amino acid biosynthesis and metabolism, and steroid-related pathways. Integrated analysis demonstrated coordinated correlations between key DEGs and differential metabolites, particularly in pathways involved in steroidogenesis, nutrient transport, and amino acid metabolism. These findings suggest that GDF9 may promote early ovarian development through coordinated regulation of gene expression and metabolic activity. As a supplementary molecular additive, GDF9 shows promise for improving hormone-based induction strategies in Japanese eel and may provide useful insights for enhancing artificial reproduction in other teleost species.