Effects of L-Carnitine and Fenofibrate on Lipid Metabolism, Oxidative Status, and Flesh Quality of Yellow River Carp (Cyprinus carpio).

This study aimed to investigate the regulatory effects of dietary supplementation with L-carnitine and fenofibrate under high-fat (HF) diet conditions. Yellow River carp (Cyprinus carpio; initial body weight 156 g) were assigned to control (CO), HF, L-carnitine supplements at 200 and 500 mg/kg (L200 and L500), and fenofibrate supplements at 200 and 500 mg/kg (F200 and F500). Each group consisted of three cages and was reared for 8 and 12 weeks to assess both short-term and long-term responses. At 8 weeks, compared to the CO group, the HF group showed a higher weight gain rate (WGR), intraperitoneal fat index (IFI), serum triglyceride (TG), intramuscular fat (IMF), and elevated hepatopancreas malondialdehyde (MDA) and alanine aminotransferase (ALT). At 12 weeks, only WGR decreased slightly compared to 8 weeks, whereas IMF, IFI, and MDA remained higher than the CO group (p  < 0.05). Both L-carnitine and fenofibrate reduced IMF at 8 and 12 weeks and increased muscle hardness, chewiness, and gumminess. Additionally, the L500 increased the muscle glutathione peroxidase (GSH-Px) at 8 weeks, and the F200 increased the GSH-Px at 12 weeks (p  < 0.05). Muscle fiber analysis showed reduced diameter and increased density in the L200 group at 8 weeks and increased fiber density in the F500 group at 12 weeks. At the molecular level, both supplementations upregulated muscle peroxisome proliferator-activated receptor γ coactivator 1-α (pgc-1α), 5'-AMP-activated protein kinase alpha 2 (ampkα2), and carnitine acyl transferase 1 (cpt-1), while lipogenic gene fatty acid synthase (fas) was downregulated in the F200 and F500 groups, and sterol regulatory element-binding protein 1 (srebp1) was reduced in the F500 group (p < 0.05). At 12 weeks, fas remained downregulated in all supplementation groups, and pgc-1α remained upregulated in the L200 group, whereas cpt-1, ampkα2, and pgc-1α were increased in the F200 group (p < 0.05). Overall, L-carnitine and fenofibrate effectively mitigate HF-induced lipid overaccumulation and oxidative stress, thereby enhancing muscle structural integrity and nutritional value in Yellow River carp.