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The aim of the study was to investigate the effects of fresh fish oil (FFO) and oxidized fish oil (OFO) diets on the muscle quality of hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu). Hybrid grouper were fed with diets containing 9% FFO or OFO for 60 days. Muscle sample were collected at 0, 30, and 60 days and the selected indexes of muscle were measured. Malondialdehyde (MDA), reactive oxygen species (ROS), total cholesterol (TC) and triglycerides (TG) in grouper muscle accumulated gradually with prolonged ingestion time, especially OFO group. Total saturated fatty acids (ΣSAFA) was significantly reduced and total polyunsaturated fatty acids (ΣPUFA) was significantly increased of muscle in FFO group; meanwhile, the muscle ΣSAFA and monounsaturated fatty acids (ΣMUFA) contents in the OFO group were significantly higher than those in the FFO group and the ΣPUFA (especially C22:5n3, C22:6n3) contents was significantly lower than that in the FFO group at 60 days. Consumption of OFO diet for 60 days reduced the diversity of volatile compounds, significantly reduced the content of total esters and increased the content of total aldehydes and total aromatics in grouper muscle. Furthermore, ingestion of OFO diet significantly reduced the mRNA expression of fraction growth factors and antioxidant genes in the muscle of grouper. In conclusion, the increasing MDA content in FO and the oxidative rancidity of PUFA can cause the deterioration of grouper quality and flavor due to oxidative muscle damage.

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This study was conducted to evaluate the effect of dietary choline levels on growth performance, liver histology, lipid metabolism and related gene expression of hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatus) fed high-lipid diets. The fish (initial body weight 6.86 ± 0.01   g ) were fed diets containing different choline levels (0, 5, 10, 15, and 20 g/kg, named D1, D2, D3, D4, and D5, respectively) for 8 weeks. The results shows that (a) dietary choline levels had no significant effect on the final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) compared with the control group ( P > 0.05 ); (b) with the increase in choline levels, triglyceride (TG), total cholesterol (TC), lipoprotein lipase (LDL), and high-density lipoprotein (HDL) of serum, all showed a tendency to increase and then decrease, and the maximum values were obtained in the D4 group ( P < 0.05 ); (c) TG and TC in the liver showed a tendency to decrease first and then increase with the dietary choline levels and reached the minimum value in D3 and D4 groups, respectively ( P < 0.05 ); (d) with increased choline levels, hepatic lipase (HL), lipoprotein lipase (LPL), adipose triglyceride lipase (ATGL), and fatty acid synthetase (FAS) in the liver all showed a tendency to increase and then decrease, and the maximum values were obtained in the D4 group, except ATGL that the maximum value was obtained in the D3 group ( P < 0.05 ); (e) oil red staining showed that dietary choline significantly reduced hepatic lipid deposition; (f) choline supplementation significantly upregulated the expression of lipolytic genes lipoprotein lipase (lpl), hormone-sensitive lipase (hsl), and peroxisome proliferator-activated receptor α (pparα) and inhibited the expression of lipid synthesis genes fatty acid synthetase (fas), acetyl-CoA carboxylase α (accα), and peroxisome proliferator-activated receptor γ (pparγ). In summary, choline can promote lipid metabolism of hybrid grouper by regulating lipid metabolism-related enzyme activity and gene expression and mitigating the negative effects of high-lipid diets.

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