Effects of Dietary DHA/EPA Ratios on Fatty Acid Composition,Lipid Metabolism‐related Enzyme Activity,and Gene Expression of Juvenile Grass Carp,Ctenopharyngodon idellus

To determine the effects of docosahexaenoic acid/eicosapentaenoic acid (DHA/EPA) ratios on grass carp, Ctenopharyngodon idellus, a 38‐d feeding trial was conducted using six isonitrogenous and isoenergetic semi‐purified diets containing constant n‐3 long‐chain polyunsaturated fatty acid (LC‐PUFA) (0.5% of dry matter), but varying ratios of DHA to EPA and a control diet (no n‐3 LC‐PUFA was included). The results revealed higher final weight and specific growth rate in the DHA/EPA 0.21 group. The n‐3 LC‐PUFA content increased in the CK (control) groups compared with that in the control diet. Lipoprotein lipase (LPL) activity increased in the treatment groups. Malate dehydrogenase showed lower activity in the DHA/EPA 1.08 group, as well as to the change in the level of glucose‐6‐phosphate dehydrogenase (G6PDH). The gene expressions of LPL increased in the treatment groups and that of peroxisome proliferator‐activated receptor α gene showed higher expressions in DHA/EPA 1.08, 0.49, and 0.21 groups. However, no remarkable differences were found among the six groups in the peroxisome proliferator‐activated receptor γ gene expression. Our findings indicated that dietary n‐3 LC‐PUFA affected fatty acid composition and lipid metabolism of grass carp. Further, fish achieved the best effect in decreasing the lipid accumulation when dietary DHA/EPA ratio was not greater than 1.