Dietary L-carnitine and nucleotides synergistically enhance growth performance, feed utilization, and antioxidant capacity of largemouth bass (Micropterus salmoides) juvenile fed a high-fat diet

Dietary L-carnitine (LC) and nucleotides (NT) are additives used independently in fish feeds. However, whether they work antagonistically or synergistically in fish nutrition is currently unknown. We explored the interactive effect between dietary LC and NT on growth performance, feed utilization, antioxidant capacity, and hepatic lipid metabolism in juvenile largemouth bass (Micropterus salmoides) juvenile fed a high dietary lipid level of 160 g/kg. Four experimental diets including basal diet (BD; no additives), 0.2 g/kg LC and 0 NT g/kg (LCNT0), 0.2 g/kg LC and 5 g/kg NT (LCNT5), and 0.2 g/kg LC and 10 g/kg NT (LCNT10) were formulated. These diets were administered twice daily to 30 fish weighing 10.3 ± 0.2 g in triplicate tanks for 9 weeks. We found that fish reared on diet LCNT10 increased significantly final body weight and weight gain than those reared on BD and LCNT0 diet (P ˂ 0.05). Feeding LCNT5 diet increased significantly feed intake than LCNT0 diet (P < 0.05). Fish fed with LCNT0 and LCNT10 diets lowered significantly FCR compared to BD and LCNT5 diet (P ˂ 0.05). Retention efficiency of nitrogen, phosphorus, and energy increased significantly in fish fed with LCNT10 diet than on BD and LCNT0 diet (P ˂ 0.05). The LCNT0, LCNT5, and LCNT10 diets reduced serum superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and malondialdehyde content of largemouth bass than BD (P < 0.05). Furthermore, LCNT5 and LCNT10 diets increased liver GSH-Px and CAT activities in fish compared to BD (P < 0.05). The BD upregulated the mRNA expression of carnitine palmitoyltransferase-1 and peroxisome proliferators-activated receptor α genes than LCNT0, LCNT5, and LCNT10 diets (P < 0.05). Taken together, dietary LC and NT supplementation synergistically promote growth rate, feed utilization efficiency, and antioxidant capacity in juvenile largemouth bass.