Dietary supplementation of ornithine improved the growth, immune response and acute NH3 stress tolerance of Pacific white shrimp, Penaeus vannamei

Ornithine is an arginine family amino acid and is not incorporated into protein. This study evaluated its role in growth, immune response and acute NH 3 stress tolerance of Penaeus vannamei . Six diets with graded levels (0.6, 0.9, 1.2, 1.5, 1.8, 2.1 g kg −1 ) of L-ornithine were formulated, and fed the shrimp for 8 weeks. The growth of shrimp was significantly improved with the dietary ornithine levels increased from 0.6 to 1.5 g kg −1 . Feed efficiency, protein efficiency ratio and protein productive value showed a similar trend to the growth performance of shrimp. Whole body protein and muscle lipid of shrimp were significantly increased in shrimp fed 1.8 g kg −1 ornithine compared to those fed 0.6 g kg −1 ornithine. The contents of several amino acids were increased with the dietary ornithine increased to 1.5 g kg −1 . Elevated levels of ornithine increased the Nitric Oxide (NO) content and suppressed arginase activity in the hemolymph. The relative mRNA expression of superoxide dismutase , heat shock protein 70 , dorsal and caspase 3 were increased with the dietary addition of ornithine, while the mRNA level of arginase was decreased with the increasing dietary ornithine levels. After 9 h acute NH 3 stress, mortality of shrimp reduced with the increasing dietary ornithine levels. The relative mRNA levels of superoxide dismutase , heat shock protein 70 , dorsal and catalase were increased with the dietary addition of ornithine after the acute NH 3 stress. The second-order regression analysis of weight gain and survival after acute stress revealed that the suitable ornithine content in the shrimp diet was 1.4–1.5 g kg −1 .