Abstract: The present study was conducted to determine the effect of small peptides on growth performance and non-specific immune of Penaeus vannamei. Four isonitrogenous and isoenergetic experimental diets were formulated. Diet containing no small peptides served as the control diet. The other three trial diets was added 1%, 2%, 3% small peptides respectively. After 60 d-feeding, growth rate, serum antibacterial activity, lysozyme activity and phenol oxidase(PO) activity were measured, a challenge test was conducted with Vibrio harveyi. The results showed that there was significant difference in length gain, weight gain, feed coefficient and survival rate (P<0.05) of Penaeus vannamei among the control group and the treatments. The length gain of 1%, 2% and 3% trial group was 17.74%, 27.75% and 17.46% higher than that of the control, respectively. The weight gain of shrimp was 12.15%, 31.16% and 19.01% higher than that of the control, respectively. The feed coefficient was 21.57%, 33.99% and 25.49% lower than that of the control, respectively. The survival rate was 12.23%, 18.89% and 8.89% higher than that of the control, respectively. Small peptides significantly enhanced(P<0.05)non-specific immune activity of Penaeus vannamei. The antibacterial activity of 1%, 2% and 3% trial group were 21.05%, 42.10% and 10.53% higher than that of the control, respectively. The lysozyme activity were 16.54%, 24.56% and 15.54%, PO activity were 25.70%, 41.90% and 24.02% higher than that of the control, respectively. The results of Vibrio harveyi challenge showed that cumulative mortality of the control in the five days was 96.7% and higher than that of the trial groups. It was concluded that the upper limit of small peptides for optimal growth performance and non-specific immune function in Penaeus vannamei feed was about 2%．

Key words: small peptides, Penaeus vannamei, larvae, growth, non-specific immunity