Abstract: The discovery and developing of new protein feedstuff have always been an important research focus in aquatic feed industry. To evaluate the effects of new protein feedstuff Clostridium autoethanogenum protein (CAP) in aquatic feed, oriental river prawn (Macrobrachium nipponense) was studied to detect the growth performance, protein and lipid metabolism when it was fed diet with CAP replacing fishmeal (FM). Six isonitrogen and isolipids diets were formulated including D1 (control group with 25% FM), D2 (CAP replacing 2.5% FM), D3 (CAP replacing 5.0% FM), D4 (CAP replacing 7.5% FM), D5 (CAP replacing 10.0% FM), and D6 (CAP replacing 12.5% FM). A total of 1200 oriental river prawns (average initial body weight 0.102±0.001 g) were randomly divided into six treatments with four replicates. The feeding trail lasted for 8 weeks. Results showed no significant differences in survival rate of prawns in each treatment (P>0.05). The weight gain rate (WGR), specific growth rate (WGR), feed coefficient ratio (FCR), and protein efficiency ratio (PER) of prawns fed diet with CAP replacing 5.0% FM were not significantly different from those in the control group (P>0.05). However, when CAP replaced more than 5.0% FM, the WGR, SGR, and PER significantly decreased, while FCR significantly increased compared to the control group (P<0.05). The whole body composition of prawns, including moisture, crude protein, lipid, and ash, was not significantly affected by the diet with CAP replacing FM (P>0.05). Notably, the non-essential amino acid content, total amino acid content, and especially glycine content in the prawn muscle significantly increased when CAP partially replaced FM in the diet (P<0.05). The total hemolymph protein of the prawn fed diet with CAP replacing 2.5% FM was not significantly different with that of the control group (P>0.05). The hepatopancreatic lipase activities were significantly higher in the D2 group than those in the control group (P<0.05). However, hemolymph total cholesterol and triglycerides were significantly lower, while hemolymph glucose was significantly higher in the prawns fed diet with CAP replacing more than 2.5% FM compared to that in the control group (P<0.05). Gene expression analysis revealed that the relative expression of tor and sr-bⅠ significantly up-regulated in the prawns fed diet with CAP replacing 5.0% FM than that in the control group (P<0.05). Moreover, when CAP replaced more than 5.0% FM, the relative expressions of s6k1, atf4, acc, fas, and hsl were up-regulated significantly compared to the D2 group (P<0.05). Except for the tor and sr-bⅠ genes in D3 group and the fas gene in D6 group, the relative expressions of genes related to protein and lipid metabolism in the hepatopancreas showed no significantly difference from those of the control group (P>0.05). In conclusion, CAP can replace about 5.0% FM in the diet of M. nipponense without negative effect on growth performance. CAP holds potential as a novel feed ingredient in the aquaculture industry.