Objectives The effects of growth trait selection on the genes expression and metabolites levels in the eggs of landlocked Oncorhynchus masou were investigated by transcriptomics and metabolomics.

Methods Collected 15 non selected landlocked O. masou and 15 the fifth generation (F₅) of selected landlocked O. masou egg tissue, and the differences in gene expression and metabolites levels between the eggs of the two species were analyzed by combining transcriptomics and metabolomics.

Results The results of the transcriptome analysis revealed a total of 10,880 differentially expressed genes (DEGs), primarily enriched in ribosomes, oxidative phosphorylation, lysosomes, and FoxO signaling pathways. Compared to generation F₅ of selected and non selected landlocked O. masou showed increased expression of genes related to oocyte development, including gonadotropin (Gn), gonadotropin-releasing hormone (Gnrh), and follicle-stimulating hormone (FSH). Additionally, the expression of genes related to oocyte development, such as gonadotropin-inhibitory hormone (GnIH), was decreased. The results of the metabolomics analysis revealed 583 differentially expressed metabolites. Among these, the levels of Vn, AKP, MDH, α-tocopherol, DHA, and EPA were higher in the selected group compared to the non-selected group. Conversely, the levels of vitamin B2, spermine, and adenosine were lower in the selected group compared to the non-selected group. The combined analysis revealed that phospholipid, lysine, glucose and fatty acid metabolic signaling pathways participate in ovarian development by enhancing lipid and fatty acid metabolic pathways.

Conclusions Continuous selection had significant effects on gene expression and metabolite levels of landlocked O. masou eggs, and phospholipid, lysine, glucose and fatty acid metabolic signaling pathways played important roles in the development of ovarian and egg.