Effects of different dietary ratios of docosahexaenoic to eicosapentaenoic acid (DHA/EPA) on the growth, non-specific immune indices, tissue fatty acid compositions and expression of genes related to LC-PUFA biosynthesis in juvenile golden pompano Trachinotus ovatus

The n-3 long chain polyunsaturated fatty acid (n-3 LC-PUFA) such as docosahexaenoic and eicosapentaenoic acids (DHA and EPA) are essential fatty acids for marine carnivorous fish. Thus, the determination of optimal dietary DHA/EPA ratio is essential for the development of better feed formulation. In the present study, a marine carnivorous fish species, golden pompano (Trachinotus ovatus) juveniles were subjected to six isoproteic and isolipidic diets contained differential ratios of DHA/EPA (0.53, 0.81, 1.17, 1.48, 1.69, and 2.12) and a constant level of n-3 LC-PUFA (1.20% of the dry weight). After the 10-week feeding trial, fish fed the diet with DHA/EPA ratios of 1.17 and 1.48 achieved the best growth performance, with significantly higher weight gain (WG) and specific growth rate (SGR) than that fish fed the other diets (P < .05). At the DHA/EPA ratio of 1.48 group, non-specific immune indices, including the activities of lysozyme (LZM), catalase (CAT) and superoxide dismutase (SOD) in serum were significantly higher than those of other groups (P < .05). Fatty acid compositions of T. ovatus muscle, liver, eye and brain were significantly affected by the diets. The content of DHA and DHA/EPA in muscle, eye and brain both markedly increased with increasing dietary DHA/EPA ratios, and the concentration of DHA in brain was much higher than other tissues. Both the expression of elovl5-like and Δ6 fad in liver and the expression of elovl4-like and Δ6 fad in brain significantly increased with increasing dietary DHA/EPA ratios (P < .05). When subjecting the WG to the second-order polynomial regression analysis, the maximal growth was achieved at 1.40 of DHA/EPA ratio for the juvenile T. ovatus, which was thought as the recommended optimum requirement of dietary DHA/EPA ratio in the current study.