We studied the effects of four strains of Bacillus isolated from the guts of healthy wild adult shrimp on survival and rate of development of whiteleg shrimp Litopenaeus vannamei larvae to understand how endemic Bacillus probiotic strains improve the health of larvae. This included bacterial isolation, assays of hemolytic activity, antagonism against pathogenic Vibrio species, growth, and adhesion to shrimp intestinal mucus, and molecular identification. Bacillus strains were tested on larval shrimp using a daily concentration of 1×10⁵CFUmL^–1, starting each bioassay at nauplii V at a density of 225 nauplii L⁻¹. Inoculations of four natural, commercial products and antibiotic oxytetracycline were added directly to the water. All treatments induced a significant increase in survival compared to the control, with strain YC5-2 showing the highest survival (~67%), followed by Alibio^MR (~57%). A mix of two strains induced the highest rate of development (7.00), followed by Alibio^MR (6.35). The results showed remarkable antagonistic activity by the four non-hemolytic Bacillus strains against Vibrio campbelli, V. vulnificus, V. parahaemolyticus, and V. alginolyticus and the potential and efficiency of probiotics isolated from shrimp gut to improve survival of shrimp larvae.