Systemic effect of dietary lipid levels and α-lipoic acid supplementation on nutritional metabolism in zebrafish (Danio rerio): focusing on the transcriptional level.

Considering the excessive lipid accumulation status caused by the increased dietary lipid intake in farmed fish, this study aimed to investigate the systemic effect of dietary lipid levels and α-lipoic acid supplementation on nutritional metabolism in zebrafish. A total of 540 male zebrafish (0.17 g) were fed with normal (CT) and high lipid level (HL) diets for 6 weeks, then fed on 1000 mg/kg α-lipoic acid supplementation diets for the second 6 weeks. HL diets did not affect whole fish protein content, but increased ASNS expression (P < 0.05). Dietary α-lipoic acid increased whole fish protein content, and decreased the expressions of protein catabolism-related genes in muscle of high lipid level groups (P < 0.05). Furthermore, HL diets increased the whole fish lipid content and the expressions of gluconeogenesis and lipogenesis-related genes (P < 0.05), and α-lipoic acid counteracted these effects and decreased the whole fish triglyceride and cholesterol contents and expressions of lipogenesis-related genes, with the enhanced expressions of lipolytic genes, especially in high lipid groups (P < 0.05). HL diets did not affect hepatocyte mitochondrial quantity or the mRNA expressions of mitochondrial biogenesis and electron transport chain-related genes; they were significantly increased by dietary α-lipoic acid (P < 0.05). These results indicated that high dietary lipid promotes lipid accumulation, while α-lipoic acid increases protein content in association of enhanced lipid catabolism. Thus, dietary α-lipoic acid supplementation could reduce lipid accumulation under high lipid, which provides a promising new approach in solving the problem of lipid accumulation in farmed fish.