Acute hepatopancreatic necrosis disease (AHPND), attributed to the production of PirA/PirB toxins by certain Vibrio sp. strains, poses a significant threat to global shrimp aquaculture, causing substantial mortality and economic losses. To enhance our understanding of this disease within a closed culture system on the northern coast of Peru, we conducted a comparative analysis of the gut microbiomes between healthy and diseased postlarvae. Diseased postlarvae were obtained through exposure to an AHPND-causing strain of Vibrio parahaemolyticus. Five healthy and five diseased postlarvae were randomly sampled from experimental rearing tanks, and their medial guts were extracted. High-throughput sequencing targeting the V4 region of the 16S rRNA gene was employed for amplicon library construction, and assessments of alpha and beta diversities and taxonomic composition were conducted. Our results revealed reduced diversity and distinct compositional profiles in the gut microbiomes of diseased postlarvae. The order Rhodobacteriales was dominant in the gut microbiomes of healthy postlarvae. In contrast, the order Vibrionales (including an unassigned genus within Vibrionales, Vibrio, and Pseudoalteromonas) exhibited the highest abundance in diseased postlarvae. In conclusion, exposure to an AHPND-causing strain of V. parahaemolyticus induces significant dysbiosis in the gut microbiome of whiteleg shrimp postlarvae.