Growth performance, antioxidant ability, biochemical index in serum, liver histology and hepatic metabolomics analysis of juvenile hybrid grouper (♀ Epinephelus fuscoguttatus x ♂ Epinephelus lanceolatus) fed with oxidized fish oil

Fish oil oxidation is a common phenomenon in aquaculture and produces harmful substances that can cause oxidative stress to aquatic animals. However, the metabolic mechanism of oxidized fish oil in the liver of hybrid groupers (female Epinephelus fuscoguttatus x male Epinephelus lanceolatus) is still unclear. In this study, a rearing experiment was conducted for 65 days with diets containing 0, 3, 6, and 9% oxidized fish oil (referred to as R, L, M, and H respectively) to investigate the effect of oxidative stress on growth performance, liver antioxidant status, biochemical index in serum, liver fat accumulation and hepatic metabolism profile of juvenile hybrid groupers. The results showed the oxidized fish oil inhibited the growth performance of grouper, and the growth performance became worse as the proportion of oxidized fish oil in the diet increased. Meanwhile, oxidized fish oil caused oxidative stress in the liver by reducing antioxidant enzyme activity and increasing the content of malondialdehyde. In addition, oxidative stress disrupted lipid metabolism by lowering low-density lipoproteins and increasing elevated-density lipoproteins in serum, and promoted the formation of fatty livers. To explore the mechanism of oxidative stress in the liver, the samples in the fresh fish oil group and the highest oxidized fish oil group were selected for non-targeted metabolome analysis. The differential metabolites in the livers were mainly phosphatidylcholines, phosphatidylethanolamines, and lysophosphatidylchoines with an upregulated status under oxidative stress. The liver responded to oxidative stress through the glycerophospholipid metabolism and choline metabolism in cancer pathways. In conclusion, oxidized fish oil inhibited growth in hybrid grouper and caused oxidative stress and fat accumulation in the liver. This oxidative stress, in turn, changed the hepatic metabolism profile.