Regulation of growth performance and lipid metabolism by dietary n-3 highly unsaturated fatty acids in juvenile grass carp, Ctenopharyngodon idellus

To determine the effects of n-3 highly unsaturated fatty acids (HUFAs) in grass carp (Ctenopharyngodon idellus), 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 HUFAs. Weight gain, specific growth rate, feed efficiency and protein efficiency increased by increasing the dietary HUFAs content from 0% to 0.52%, and declined thereafter. Intraperitoneal fat content and the hepatopancreatic lipid levels were lowest in the 0.52% group. The tissue fatty acid level was well correlated with dietary HUFAs content. Hepatic lipoprotein lipase (LPL) activity was significantly higher in the 0.52% group, while that of malate dehydrogenase (MDH) was stable in the 0-0.52% groups, and was significantly lower in the 1.13% group. Superoxide dismutase (SOD) activity increased significantly with increasing dietary HUFAs content, consistent with the level of malondialdehyde (MDA). 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 HUFAs content up to 0.83%. These results indicate that adequate dietary HUFAs supplementation significantly promotes growth performance and lipid metabolism in freshwater fish grass carp. However, excess HUFAs fortification may exert adverse effects, which might be due to oxidative stress.