| To evaluate the effect of n-3 HUFA on growth performance and lipid metabolism in grass carp. Two trial were designed, including dietary n-3 HUFA content (feed 75d) and DHA/EPA ratio (feed 38d). Some indicators were detected, including growth performance, fatty acid profiles, activities of lipogenesis-related enzymes, expression of lipid metabolism-related genes and anti-oxidation status. The result showed:(1)a 75-day feeding experiment was conducted using five isonitrogenous and isoenergetic semi-purified diets containing 0% (control), 0.26%, 0.52%, 0.83% or 1.13% n-3 HUFA. Weight gain, specific growth rate, feed efficiency and protein efficiency increased by increasing the dietary n-3 HUFA content from 0% to 0.52% (P<0.05), and declined thereafter. Intraperitoneal fat content and the hepatopancreatic lipid levels were lowest in the 0.52% group (P<0.05). The tissue fatty acid level was well correlated with dietary n-3 HUFA content. Hepatic lipoprotein lipase (LPL) activity was significantly higher in the 0.52% group (P<0.05), while that of malate dehydrogenase (MDH) was stable in the 0–0.52% groups, and was significantly lower in the 1.13% group (P<0.05). Superoxide dismutase (SOD) activity increased significantly with increasing dietary HUFA content, consistent with the level of malondialdehyde (MDA) (P<0.05). Hepatic mRNA expression of peroxisome proliferator-activated receptor-α(PPAR-α) was greatest in the 0.83% group and that of the LPL gene increased with increasing dietary n-3 HUFA content up to 0.83% (P<0.05).(2)A total of 198 grass carp juveniles (body weight (17.6±1.2)g) were randomly assigned into six groups with triplicate, total 18 tanks with 11 fish each. Grass carp juveniles were reared in glass-steel tanks (200-L volume per tank) with a continuous flow of water and aeration, temperature 28–30°C, dissolved O2 6–8mg/L and pH 7.5–7.7. Grass carp juveniles were fed for 38 days using six experimental diets (CK and I to V) with the same amount of DHA and EPA (0.5% of dried diet), but varying ratios of DHA to EPA (4.93,2.05,1.08,0.49 and 0.21 respectively) and a control diet (CK, no DHA and EPA included ). Final weight, weight gain and specific growth rate in treatment V were significantly higher in control group (P<0.05). The feed efficiency and protein efficiency were significantly higher in treatment I, II, III, IV and V (P <0.05), however, there were no statistically significant differences among treatment I to V. Muscle lipid content in treatment II and III were significant higher (P <0.05). Hepatopancreas lipid content in treatment I to V were significant lower than control group (P <0.05), however, there were no statistically significant differences in hepatopancreas lipid content among treatment I to V. The activities of lipoprotein lipase (LPL) were significantly higher in treatment I, II, III, IV and V (P <0.05), however, there were no statistically significant differences among treatment I to V. The activities of Glucose-6-phosphate dehydrogenase (G6PDH) and Malate Dehydrogenase (MDH) kept constant in all groups (P >0.05); The activities of total anti-oxidative capacity (T-AOC) were no statistically significant differences among groups. The activities of catalase (CAT), SOD and the content of MDA) kept constant in all groups (P >0.05). The activities of total antioxidative capacity (T-Aoc) in control group was significantly higher than treatment I to IV (P <0.05)Conclude: adequate dietary n-3 HUFA supplementation significantly promotes growth performance and lipid metabolism through PPAR-αand LPL in freshwater fish grass carp. However, excess n-3 HUFA fortification may exert adverse effects, which might be due to oxidative stress. Adequate n-3 HUFA could adjust the distribution of body fat among tissues, also might induce oxidative stress, but the growth performance, lipid accumulation and antioxidation system not in?uenced by the ratios of DHA/EPA (4.93–0.21) . |
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