Study On High Efficiency And Low Nitrogen Ecological Feed For Penaeus Vannamei

The problems of high feed protein content and low utilization rate in Penaeus vannamei aquaculture generally lead to serious eutrophication of aquatic environment,frequent diseases and low success rate in shrimp aquaculture.Reducing feed protein content and improving feed utilization rate are undoubtedly effective ways to solve these problems.Therefore,the aim of this study was to develop an efficient and low nitrogen ecological feed for P.vannamei.Nine kinds of feed were designed and manufactured by four factors and three levels orthogonal design.The feed was fed to P.vannamei for six weeks.The optimum dietary protein,fat,calcium and phosphorus contents were screened by taking specific growth rate of the shrimp as a consideration index.Adding 0,0.5%,1%and 2%Chlorella vulgaris to the basic feed,the optimum dosage of C.vulgaris was determined by measuring the growth index,digestive enzyme activity and immune related enzyme activity.The results showed that the optimum dietary protein,fat,calcium and phosphorus contents were 36.93%,6.89%,2.59%and 1.12%respectively.The effect of C.vulgaris on P.vannamei increased with the increase of its dosage.When the dosage increased from 1%to 2%,the effect tended to be stable,and the optimum dosage of C.vulgaris was 1%.RT-PCR and real-time fluorescence quantitative PCR were used to investigate the effects of C.vulgaris on Toll-like receptor(Toll),IMD immune signaling pathway(IMD),prophenoloxidase(proPO),catalase(CAT),lysozyme(Lyz)and manganese superoxide dismutase(cMnSOD)gene expression.The results showed that C.vulgaris could significantly increase the relative expression of Toll and cMnSOD genes in hepatopancreas of P.vannamei(p<0.01,p<0.05),but had no significant effect on the relative expression of other immune related genes(p>0.05);C.vulgaris could significantly increase the relative expression of cMnSOD genes in hemolymph of P.vannamei(p<0.05),but had no significant effect on other immune related genes(p>0.05).The fatty acid composition of C.vulgaris feed and muscle of P.vannamei was analyzed by gas chromatography.The results showed that the types of fatty acids detected in 1%C.vulgaris feed were the same as those in control feed,and the proportion of total polyunsaturated fatty acids(PUFA)and total PUFA in C.vulgaris feed was slightly higher than that in control feed(p>0.05,P>0.05).Fourteen kinds of fatty acids were detected in the muscle of 1%C.vulgaris group and control group,and the PUFA content of shrimp muscle was 53.55%and 53.51%,respectively.There was no significant difference(p>0.05).However,the contents of arachidonic acid(ARA),eicosapentaenoic acid(EPA)and docosahexaenoic acid(DHA)in 1%C.vulgaris group were higher than those in control group(p<0.05,p<0.01,p<0.01).In addition,high throughput sequencing results confirmed that C.vulgaris could significantly improve the intestinal flora composition of P.vannamei.Compared with the commercial feed,the developed ecological feed can significantly improve the survival rate and specific growth rate of P.vannamei,although the protein content of the ecological feed is significantly reduced.