Effects of different dietary linolenic acid/linoleic acid ratios on growth performance and fatty acid composition of juvenile Litopenaeus vannamei.

This experiment was conducted to study the effects of different dietary linolenic acid (C18:3n-3)/linoleic acid (C18:2n-6) ratios on growth performance and fatty acid composition of juvenile Litopenaeus vannamei.Four isonitrogenous diets with crude fat level at about 7.2% were formulated using three different lipid sources (fish oil,linseed oil and soybean oil) in variable proportions to prepare diets with different C18:3n-3/C18:2n-6 ratios of 0.17,0.30,0.56 and 0.68,respectively.Four hundred and eighty juvenile Litopenaeus vannamei with an average body weight of (0.573±0.002) g were randomly divided into 4 groups (3 replicates per group and 40 shrimp each replicate),and remarked L0.17,L0.30,L0.56 and L0.68.The experiment lasted for 8 weeks.Results showed as follows:with the C18:3n-3/C18:2n-6 ratio increasing,weight gain rate of shrimp was increased firstly and then decreased while feed conversation rate was decreased firstly and then increased,but the difference was not significant among all groups (P0.05).According to the bivariate regression analysis,the relationship between the weight growth rate (y) and the C18:3n-3/C18:2n-6 ratio (x) as was y=-1 333.2x2+1 175.5x+785.66 (R2=0.723 8).As C18:3n-3/C18:2n-6 ratio was 0.44,juvenile shrimp showed the highest weight gain rate.The highest crude protein content of the whole body was found in L0.68 group which was significantly higher than that in other groups (P0.05).There was no significant difference on moisture and crude fat contents of the whole body and hepatopancreas index among all groups (P0.05).The contents of C18:2n-6 and C18:3n-3 in muscle of all groups were lower than those in hepatopancreas,but the contrary was for the contents of C20:4n-6,C20:5n-3 (EPA) and C22:6n-3 (DHA).The content of EPA in hepatopancreas in L0.68 group was markedly higher than that in L0.30 group,and the content of DHA in hepatopancreas in L0.68 group was significantly higher than that in other groups (P0.05).In muscle,the highest contents of EPA and DHA were found in L0.30 group,but no significant difference was found among all groups (P0.05).In conclusion,the dietary C18:3n-3/C18:2n-6 ratio affects the growth performance of juvenile Litopenaeus vannamei to a certain extent,and significantly affects contents of C18:2n-6 and C18:3n-3 set fatty acids in hepatopancreas and muscle of juvenile Litopenaeus vannamei.When dietary C18:3n-3/C18:2n-6 ratio is 0.44,juvenile shrimp show the best growth performance.