Abstract: The effect of breeding on muscle metabolites of landlocked Oncorhynchus masou was explored by untargeted metabolomics technology, which provided a theoretical basis for breeding efforts. Muscle tissues were collected from 10 non selected landlocked O. masou and 10 fifth generation (F₅) selected individuals, with untargeted metabolomics studies using liquid-mass coupling (LC-MS) technology. Metabolite differences between F₅ selected and non-selected groups were compared, with differential metabolites identified using thresholds of P<0.05, VIP value>1.0, and FC≥1.5 (up-regulated) or FC≤0.667 (down-regulated). Pathway annotation of the metabolites through KEGG database, phenylpropane biosynthesis and metabolic, fat metabolism, and eicosanoids metabolism pathway were analyzed. Significant differences in muscle metabolites were observed between F₅ selected and non-selected groups: compared with the non-selected group, 213 differential metabolites were significantly up-regulated and 348 were significantly down-regulated, mainly annotated to secondary metabolites biosynthesis, bile secretion, and metabolism pathway. KEGG bubble chart analysis showed that phenylpropane biosynthesis, phenylalanine metabolism, and methane metabolism pathway had important effects on muscle growth during selection. Breeding exerted a significant effect on muscle metabolites in landlocked O. masou. Metabolomics analysis showed that post-selection, improvements in muscle nutritional quality relative to the non-selected group may be linked to metabolites changes such as DHA, EPA, AMPK, and PPARα in the phenylpropane biosynthesis and metabolism, fat metabolism, and arachidonic acid metabolism pathway.