| Chinese mitten crab（Eriocheir sinensis）,commonly known as river crab and hairy crab,belongs to Crustacea,Decapoda,Fangcrabidae,and Eriocheir,which is mainly distributed in rivers and lakes in the eastern coastal areas of China.As the main traditional cultured crab in China,it is also a special aquatic product in Jiangsu Province.Highly unsaturated fatty acids（HUFA）,mainly include eicosapentaenoic acid（EPA）,docosahexaenoic acid（DHA）and arachidonic acid（ARA）,which are important for the growth,metabolism,molting of crustaceans.However,few researches on the ARA requirement of E.sinensis have been explored,and restricting the healthy development of river crab aquaculture.It has great theoretical and rarely significance to explore the influence of dietary ARA on E.sinensis.Therefore,this study investigated the effects of dietary ARA on the survival,growth,fatty acid composition,non-specific immunity and antioxidant capacity,intestinal inflammatory factors and intestinal flora of mitten crab juveniles,so as to evaluate the appropriate amount of dietary ARA by E.sinensis,to provide reference for healthy aquaculture and functional feed development of crabs.1.A 12-week feeding trial was conducted to determine the effect of dietary arachidonic acid（ARA）levels on growth performance,feed utilization,muscle fatty acid composition and body proximate composition of juvenile Chinese mitten crab,E.sinensis.Six experimental diets containing 0.11%（control group）,1.20%,2.37%,3.52%,4.76%and 7.39%ARA of total lipid content were formulated,to feed six groups of crabs（the initial weight,1.01±0.12 g）,respectively.No significant differences were found in survival rate among dietary treatments.Crabs fed with the 2.37%of total lipid content showed the highest final weight（Wt）,weight gain rate（WGR）and specific growth rate（SGR）.The highest feed conversion ratio（FCR）was found in crabs fed with the control diet.Moreover,dietary ARA levels had no significant effect on the content of moisture,crude protein,crude lipid and crude ash among all six groups.By contrast,the fatty acid composition of muscle was significantly affected by dietary ARA levels.The highest C16:1n-9 and C18:1n-9 content was found in G1,the highest C18:3n-3 content was found in G5.With the dietary ARA level increased,the content of C18:2n-6 and C22:6n-3 significantly increased,the highest values were found in crabs of G6.For ARA,C22:2 and C20:5n-3,with the dietary ARA level increased,their contents increased first and then decreased,the highest values were all found in crabs of G4.Based on the results of the quadratic regression analysis of SGR,the optimum level of ARA for E.sinensis was suggested to be 4.54%of total lipid content.2.The present study aimed to evaluate the effects of ARA on the antioxidant capacity,immune response intestinal inflammatory factors and intestinal flora composition of E.sinensis.Dietary ARA level did not affect the total hemacyte counts（THC）and phagocytic activity（RBs）of crabs（p>0.05）,but RBs activity in G4 was significantly higher than that in G6（P<0.05）.Dietary ARA significantly enhanced the activity of antioxidant enzymes,including SOD,CAT,GST and GPx（p<0.05）.For two antibacterial genes,the highest gene expression of lysozyme was found in G5（p<0.05）,the highest gene expression of crustin was found in G5 and G6（p<0.05）,in contrast,the moderate dietary ARA levels（1.20%-3.52%of total fatty acids）significantly inhibited their gene expression（p<0.05）.Higher dietary ARA level significantly decreased the gene expression of IL-1β and TNF-α（p<0.05）,which indicated that ARA might be linked to reduced inflammation.Furthermore,dietary ARA significantly affected the intestinal microbiota composition（p<0.05）,and the opportunistic pathogens,including Shewanella,Vibrio,Citrobacter,CandidatusBacilloplasma,Dysgonomonas,were enriched in the intestines of crabs fed with the lowest or highest ARA level. |
