Effect of dietary oxidized fish oil on liver function in hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ Epinephelus lanceolatus)

Fish oil oxidation can produce harmful substances, but the specific effects of oxidized fish oil on liver function in the hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ Epinephelus lanceolatus) are not yet clear. In the present study, hybrid grouper was fed diets containing 0, 3, 6, or 9% oxidized fish oil (referred to as the control, L, M, and H groups respectively) for 65 days to investigate its effects on liver physiology. Oxidized fish oil significantly decreased protein content in liver (P < 0.05). Lipid content of liver in the H group was significantly higher than in the control group (P < 0.05), while eicosenoic acid in the L group was significantly lower than in the control group (P < 0.05). Oxidized fish oil substantially decreased the activities of antioxidant enzymes in liver including SOD, CAT, and GSH-Px (P < 0.05), and increased MDA levels (P < 0.05) in a dose-dependent manner. Vitamin E content of liver in the control group was significantly higher than in the L, M, and H groups (P < 0.05). IL-8 in liver was significantly lower in the M group than in the control, L, and H groups (P < 0.05). When the amount of oxidized fish oil in the diet was increased, the amount of IL-10 and TNF-α in the liver rose substantially (P < 0.05). Ballooning degeneration and nuclear migration in the liver became serious as the proportion of oxidized fish oil in the diet increased. Oxidized fish oil caused damage to the liver microstructure, including mitochondria, nucleoli, endoplasmic reticulum, and lipid droplets. The liver mainly functions as a metabolic process under oxidative stress. In detail, the liver mainly responded to oxidative stress through glycine, serine, and threonine metabolism, arginine biosynthesis, and glycerophospholipid metabolism. In conclusion, oxidized fish oil caused nutritional change, oxidative stress, inflammation, morphological abnormalities, and alterations of transcriptome in the liver.