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, nonspecific 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 Delta 6 fad in liver and the expression of elovl4-like and Delta 6 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.