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This study investigated the influence of dietary astaxanthin (AX) on glucose and lipid metabolism in rainbow trout liver. Two iso-nitrogenous and iso-lipidic diets were tested for 12 weeks in rainbow trout with an initial mean weight of 309 g. The S-ASTA diet was supplemented with 100 mg of synthetic AX per kg of feed, whereas the control diet (CTRL) had no AX. Fish fed the S-ASTA diet displayed lower neutral and higher polar lipids in the liver, associated with smaller hepatocytes and lower cytoplasm vacuolization. Dietary AX upregulated adipose triglyceride lipase (<i>atgl</i>), hormone-sensitive lipase (<i>hsl2</i>) and 1,2-diacylglycerol choline phosphotransferase (<i>chpt</i>), and downregulated diacylglycerol acyltransferase (<i>dgat2</i>), suggesting the AX’s role in triacylglycerol (TAG) turnover and phospholipid (PL) synthesis. Dietary AX may also affect beta-oxidation with the upregulation of carnitine palmitoyltransferase 1 (<i>cpt1α2</i>). Although hepatic cholesterol levels were not affected, dietary AX increased gene expression of sterol regulatory element-binding protein 2 (<i>srebp2</i>). Dietary AX upregulated the expression of 6-phosphogluconate dehydrogenase (<i>6pgdh</i>) and downregulated pyruvate kinase (<i>pkl</i>). Overall, results suggest that dietary AX modulates the oxidative phase of the pentose phosphate pathway and the last step of glycolysis, affecting TAG turnover, β-oxidation, PL and cholesterol synthesis in rainbow trout liver.