Impact of Dietary Docosahexaenoic Acid : Eicosapentaenoic Acid Ratio on Growth, Fatty Acid Composition, Lipid Metabolism, and Antioxidant Status of Juvenile Hybrid Grouper (Brown‐marbled Grouper Epinephelus fuscoguttatus ♀ × Giant Grouper E. lanceolatus ♂)

Abstract The present study was conducted to evaluate the effects of dietary docosahexaenoic acid : eicosapentaenoic acid (DHA:EPA) ratio on growth, lipid metabolism, and antioxidant status of hybrid grouper (Brown‐marbled Grouper Epinephelus fuscoguttatus ♀ × Giant Grouper E. lanceolatus ♀). Fish (initial body weight = 20.8 ± 0.03 g; mean ± SE) were fed six different isoproteic (53%) and isolipidic (7%) diets containing graded DHA:EPA ratios (D/E) of 0.54, 0.97, 1.51, 2.01, 2.41, and 2.85. No significant difference in weight gain was recorded in fish fed with different dietary DHA:EPA ratios. The DHA:EPA ratio in fish muscle was significantly increased as the dietary ratio increased. Relative messenger RNA expression of hepatic elongase of very long fatty acids 5 ( elovl5* ) and delta‐6 fatty acyl desaturase (Δ 6 fad* ) in the D/E 2.41 and 2.85 groups was significantly higher than that in the other treatments. Lipid droplet accumulation was significantly higher in the liver of the D/E 0.54 and 0.97 groups than in the other groups. Lipogenesis‐related genes (fatty acid synthase [ FAS* ] and acetyl coenzyme A carboxylase [ ACC* ]) were up‐regulated by lower dietary DHA:EPA ratios (0.54 and 0.97), whereas lipolysis‐related genes (peroxisome proliferator‐activated receptor alpha [ PPAR α * ] and hormone‐sensitive lipase [ HSL* ]) were down‐regulated. The expression of genes related to antioxidative capacity, including nuclear factor erythroid 2‐related factor 2 ( Nrf2* ), manganese superoxide dismutase ( MnSOD* ), and peroxiredoxin ( Prx* ), was significantly down‐regulated in the D/E 1.51 and 2.01 groups compared with other treatments, while Kelch‐like ECH‐associated protein 1 ( Keap1* ) was up‐regulated. The above results suggest that dietary DHA:EPA ratio influences muscle fatty acid composition and lipid metabolism by altering the expression of lipogenesis‐ and lipolysis‐related genes, and dietary DHA:EPA ratio may also regulate the antioxidant capacity of juvenile hybrid grouper.