Heat-killed Vibrio parahaemolyticus (HVp) works as an immunostimulant in Pacific white shrimp (Litopenaeus vannamei). In controlled trials, a single intramuscular dose raised haemocyte counts, phenoloxidase activity, respiratory burst, lysozyme activity, phagocytosis and bacterial clearance within three to five days, and held those gains for at least a week. When vaccinated shrimp were later challenged with live V. parahaemolyticus, survival reached 66.7% at the low dose and 70.8% at the high dose, against 45.8% in unvaccinated controls. The vaccinated groups also kept steadier haemolymph glucose and lactate profiles and showed far less hepatopancreas damage, which suggests the immune activation came without a heavy metabolic price. One boundary matters here. The strain…