Effect of dietary methionine on growth performance, lipid metabolism and antioxidant capacity of large yellow croaker (Larimichthys crocea) fed with high lipid diets

A 10-week feeding trial was conducted to evaluate the effect of dietary methionine (MET) on the growth performance, lipid metabolism and liver antioxidant function in juvenile large yellow croaker ( Larimichthys crocea ) fed with high lipid diets (HLDs). Large yellow croaker with an initial average weight of 8.59 g, were fed with basic HLD (lipid level at 18%, HL), basic HLD supplemented with 0.6% MET (HL/L-MET) and basic HLD supplemented with 1.2% MET (HL/H-MET). Results indicated that dietary MET did not affect weight gain, specific growth rate and feed efficiency ratio ( P  > 0.05). The MET supplementation in large yellow croaker also did not affect the content of total lipid in whole body (HL = 9.57, HL/L-MET = 8.92 and HL/H-MET = 8.71%), liver (7.34 , 16.68 and 14.37%) and muscle (10.87 , 12.11 and 9.94%) ( P >  0.05). However, MET supplementation reduced the size and number of liver lipid droplets as dietary MET increased. Meanwhile, supplementation of MET in HLDs reduced serum total cholesterol (2.65, 2.14 and 1.91 mmol/L), low-density lipoprotein-cholesterol (0.27, 0.21 and 0.16 mmol/L) and triglyceride (4.80, 2.43 and 1.96 mmol/L) ( P  < 0.05), but increased serum high-density lipoprotein-cholesterol (0.68, 0.77 and 0.83 mmol/L) ( P  < 0.05). Dietary MET upregulated significantly the mRNA expression of genes related to mitochondrial fatty acid β-oxidation (PPARα and CPT1) and ER stress (GRP78, ATF6α and CHOP) ( P  < 0.05). Furthermore, feeding fish with MET diets reduced serum alanine transaminase and aspartate transaminase activities, serum and liver malondialdehyde content, and liver 8-hydroxydeoxyguanosine level. Interestingly, feeding fish with MET diets increased liver total antioxidant capacity activity ( P  < 0.05). In conclusion, dietary MET improved lipid metabolism and increased antioxidant capacity in the liver, but did not affect growth performance in juvenile large yellow croaker fed with HLDs.