Dietary supplementation of L-carnitine relieved detrimental impacts of a high-fat diet in juvenile Trachinotus ovatus

In recent years, the dramatically high lipid level has been used in fish feeds, resulting in low survival rates of fish and huge economic losses. Based on these issues, a six-week feeding experiment was conducted to investigate whether diet supplements with L-carnitine can be used to relieve detrimental impacts on growth performance, hepatic lipid accumulation, antioxidant, anti-inflammatory and non-specific immune status, as well as intestinal morphology of Trachinotus ovatus, fed on a high-fat diet. Three isonitrogenous diets were formulated to either include or exclude high-fat and L-carnitine (lipid positive (LP): 130 g kg⁻¹ lipid, lipid negative (LN): 210 g kg⁻¹ lipid, lipid negative with L-carnitine (LNC): 210 g kg⁻¹ lipid with 0.6 g kg⁻¹L-carnitine). Results indicated that the growth performance and mid-intestine villi length of T. ovatus in the LN group were significantly lower than that of the LP group (p < 0.05), while significantly higher growth performance and better mid-intestine morphology of fish in the LNC group was found compared to the LN group (p < 0.05). mRNA expression levels of hepatic genes associated with the inflammatory and non-specific immune statue of T. ovatus in the LN group were significantly higher compared with the LP group (p < 0.05), while that of the LNC group was significantly lower compared with the LN group (p < 0.05). Hepatic triglyceride content and lipid droplets in the LN group were significantly elevated, compared with the LP group (p < 0.05). On the contrary, diet supplemented with L-carnitine could mitigate hepatic lipid accumulation in fish caused by a high-fat diet. Regarding antioxidant states, higher malondialdehyde content in the LN group (p > 0.05) and significantly higher levels in the LNC group (p < 0.05) were found, compared with the LP group, while no statistical difference was found between the LN and LNC groups (p > 0.05). In conclusion, L-carnitine can relieve the detrimental impact on growth performance of T. ovatus exposed to a high-fat diet treatment by reducing hepatic lipid accumulation and improving intestinal morphology, anti-inflammatory and non-specific immune status, but could not mitigate oxidative pressure.