Abstract:White shrimp Litopenaeus vannamei fed diets containing the hot-water extract of Gracilaria tenuistipitata at 0 (control), 0.5, 1.0 and 2.0 g kg− 1 for 21 days, were exposed to 5 mg L− 1 ammonia-N (ammonia as nitrogen), and immune parameters, including hyaline cells (HCs), granular cells (GCs, including semi-granular cells), the total hemocyte count (THC), phenoloxidase (PO) activity, respiratory bursts (RBs), superoxide dismutase (SOD) activity, and hemolymph protein level, were examined 6–120 h post-stress. Shrimp fed the control diet with no ammonia stress served as the background control. Results indicated that the immune parameters of shrimp fed the 2.0 g kg− 1 diet had returned to the background values at 12–24 h post-stress, whereas the immune parameters of control shrimp had returned to the background values at 72–≥ 120 h post-stress. It was therefore concluded that L. vannamei fed the extract-containing diets at 2.0 g kg− 1 or less exhibited a protective effect against ammonia stress as evidenced by the earlier recovery of immune parameters. Shrimp subjected to ammonia stress showed a greater decrease in PO activity and later recovery to the background value compared to the decrease and recovery of RBs and SOD activity indicating progressive perturbation of the humoral immunity.