Growth performance and metabolic responses of hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) to different dietary DHA/EPA ratios

This research aimed to examine how graded dietary DHA/EPA ratios influence growth performance, lipid metabolism, and antioxidant capacity in hybrid grouper ( Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂). Five experimental diets, formulated to have 48% protein and 12% lipid, were designed with DHA/EPA ratios of 0.77, 1.31, 2.44, 3.20, and 4.10. A total of 450 fish (9.87 ± 0.02 g, 40 days of age) were arbitrarily allocated into 5 groups with 3 replicates each for a 56 d experimental period. Analysis results showed that:(1) As dietary DHA/EPA ratios rose, weight gain rate (WG) and specific growth rate (SGR) exhibited a pattern of first increasing and then decreasing. WG and SGR attained its peak value in the 1.31 group, which were notably higher when compared with the control (0.77) and the highest ratio (4.10) groups ( P < 0.05). (2) The relative proportion of DHA in muscle was significantly higher than that in liver. With increasing dietary DHA/EPA ratios, the DHA/EPA ratios in both muscle and liver also increased significantly ( P < 0.05).(3) A higher DHA/EPA ratio significantly decreased the serum contents of triglycerides (TG) and glucose (GLU) ( P < 0.05). Meanwhile, it markedly increased the serum content of high-density lipoprotein cholesterol (HDL-C) ( P < 0.05). (4) When the dietary DHA/EPA ratios were 2.44 and 3.20, the activities of superoxide dismutase (SOD), catalase (CAT) and antioxidant capacity (T-AOC) in serum and liver were the highest ( P < 0.05), and the level of malondialdehyde (MDA) was the lowest ( P < 0.05). Furthermore, When the DHA/EPA ratio was 2.44, the activity and gene expression of hepatic carnitine palmitoyltransferase-1 (CPT-1) were significantly upregulated, while the activity of fatty acid synthase (FAS) was inhibited ( P < 0.05). In summary, dietary DHA/EPA ratios ranging from 1.31 to 3.20 optimized growth performance, enhanced antioxidant capacity, and modulated lipid metabolism in hybrid grouper. However, an excessively high ratio (4.10) may induce oxidative stress and inhibit growth. The WG was fitted using a quadratic regression model, and it was determined that the theoretical optimal ratio of DHA/EPA for achieving the best growth performance in hybrid grouper was 2.125, which falls within the above appropriate range.