Effects of dietary l-carnitine on growth performance, lipid metabolism, oxidative stress, mitochondrial function and endoplasmic reticulum stress of rice field eel (Monopterus albus) fed high-carbohydrate-diets

To comprehensively investigate effects of dietary l -carnitine (LC) on growth performance, lipid metabolism, oxidative stress, mitochondrial function and endoplasmic reticulum (ER) stress in farmed fish fed high-carbohydrate-diets (HCD), 960 rice field eels (17.09 ± 0.14 g) were chosen and randomly assigned to 16 cages. These fish were fed a control diet (15 % α-starch, CON), a high-carbohydrate-diets (35 % α-starch, HCD), a HCD supplementing with 1.2 ‰ LC (HC/LLC), and a HCD supplementing with 2.4 ‰ LC (HC/HLC). Results of 8-week feeding trial showed that HCD increased liver lipid content, induced liver dysfunction, oxidative stress and ER stress, but not affected growth performance. Dietary LC supplementation significantly increased weight gain rate and specific growth rate and decreased liver lipid content. In the meantime, LC reduced the activity of serum ALT, improved liver's antioxidant capacity, thereby mitigating liver damage. Dietary LC positively regulated expression of genes related to oxidative stress, such as keap1 , nrf2 , cat and sod . Furthermore, LC supplementation upregulated expression of genes related to the mitochondrial function, such as crls1 and lclat1 (cardiolipin metabolism) , pgc1α, pparα and cpt1 (mitochondrial β-oxidation) . Intriguingly, administering LC-fortified diets to fish resulted in downregulation of ER stress-related gene expression, such as grp78, ire1 and atf6 . It is first reported in this study that the incorporation of LC into the diet of HCD-fed fish facilitates lipid metabolism through concurrent enhancement of mitochondrial function, reduction of oxidative stress, and alleviation of ER stress.