Effects of dietary n-3 highly unsaturated fatty acids levels on growth, lipid metabolism and innate immunity in juvenile golden pompano (Trachinotus ovatus)

To investigate the effects of dietary n-3 highly unsaturated fatty acids (HUFA) levels on growth, lipid metabolism and innate immunity in juvenile golden pompano Trachinotus ovatus, a marine carnivorous teleost, a total of 450 fish (average body weight: 14.84 g) were randomly distributed into 18 cages at sea, each dietary group with three cages and respectively fed six diets (D1-D6) with 2.30% (D1), 0.64% (D2), 1.00% (D3), 1.24% (D4), 1.73% (D5), or 2.10% (D6) n-3 HUFA. Here, D1 with fish oil as lipid source was set as control, while D2-D6 used a mixed vegetable oil as lipid source and supplemented with docosahexaenoic acid- (DHA) and eicosapentaenoic acid-(EPA) enriched oils to adjust the n-3 HUFA levels. After 8 weeks feeding, the daily growth coefficient (DGC), specific growth rate (SGR) and feed efficiency ratio (FER) showed no significant difference among the six dietary groups (P > 0.05). The levels of EPA and DHA in serum and liver increased with the dietary n-3 HUFA levels. The activity of total superoxide disumutase (T-SOD) in serum of fish fed D4 and D5 were significantly higher than that of the other groups, whereas the opposite was true for serum IL-1 beta and IL-6 levels as well as liver malondialdehyde (MDA) content. The mRNA levels of genes related to hepatic lipid metabolism including sterol regulatory element-binding protein-1 (srebp-1), fatty acid binding protein 1 (fabp1), peroxisome proliferators-activated receptor alpha (ppara), elongase of very long-chain fatty acids 5 (elovl5) and fatty acyl desaturase 2 (fads2) were down-regulated in fish fed the diets with high n-3 HUFA levels, while those of apolipoprotein b 100 (aprob 100) and carnitine palmitoyl transferase 1 (cpt1) increased significantly as increasing n-3 HUFA levels up to 1.73% (D2-D5), but decreased in the 2.10% n-3 HUFA group (D6). In addition, the expression levels of genes related to innate immunity including interleukin-10 (il-10) and transforming growth factor beta 1 (tgf-beta 1) increased significantly when dietary n-3 HUFA increased from 0.64% to 1.73%, whereas the opposite was true for the expression levels of nuclear factor kappa-B (nf-kappa b), interleukin-1 beta (il-1 beta), interleukin-6 (il-6) and interleukin-8 (il-8). Overall, the results indicated that dietary n-3 HUFA at 1.24-1.73% (D4-D5) can effectively improve fatty acid profiles, lipid metabolism, antioxidant capacity and immune response of golden pompano.