Microalgae are a promising solution in shrimp farming overexploitation. This study assessed the efficacy of microalgae as a food additive for Penaeus vannamei growth and their effect on immune system stimulation against Vibrio parahaemolyticus. Three diets were formulated with 0, 1, and 3% (DC, D1, and D3, respectively) of a mixture of three different microalga species, Tetraselmis suecica, Dunaliella salina, and Chaetoceros muelleri, and growth, survival, and post-harvest quality in shrimp culture were evaluated. Two bioassays were performed: a 60-day feeding trial and an immersion infection bioassay against V. parahaemolyticus. D1 was the best treatment and significantly different to DC (P ≤ 0.05), achieving a food conversion factor of 1.24 ± 0.11 and 1.85 ± 0.38; specific growth rate 1.58 ± 0.03% d-1 and 1.35 ± 0.11% d-1; and weight gain of 5.68 ± 0.32 g and 4.79 ± 0.33 g, respectively. Protein content in shrimp muscle was positively increased by microalgae inclusion, achieving 20.8 ± 0.2% (D1) to 21.7 ± 0.3% (D3), 19.2 ± 0.1% (DC). In the infection bioassay, D1 and D3 reached a 100% survival rate, and histological damage in the hepatopancreas was not observed, suggesting immune system stimulation. These results indicated that microalgae added to food are an excellent source of proteins, carbohydrates, lipids, and promoters of antimicrobial activity that allowed additional protection against mortality caused by V. parahaemolyticus.