The Vibrio genus of bacteria includes several species naturally occurring in Gulf waters that can be pathogenic to larval oysters. Aquaculture facilities and hatcheries handling larval oysters are at risk of mass mortality events if these Vibrio species infect their larval stock, leading to significant economic challenges. Vibrio strains were isolated from water samples collected at two hatcheries in 2022 & 2024 following mass mortality events. After isolation and purification, selected strains were tested for pathogenicity in a 7–day experiment. Approximately 30 oyster larvae (Crassostrea virginica), which were spawned at the Louisiana Sea Grant Oyster Research Lab between April and September 2024, were exposed to about 4*104 CFU/ml of Vibrio species in 2 ml of sea water. The larvae were fed 25 µl of algae daily, also collected at the Oyster Research Lab. The graph below compares the 7-day mortality rates of several Vibrio strains to a control group (larvae suspended in sea water fed algae without Vibrio exposure).