Most bacterial diseases in aquaculture production systems are caused by Gram-negative bacteria that belong to the Vibrionaceae family. The administration of probiotics is a promising area of research for the biocontrol and prevention of diseases in aquaculture. In this work, the objective was to investigate three probiotic strains of the genus Lactobacillus. Two trials were performed to determine the mean effective dose of the Lactobacillus strains and the mean lethal dose of the pathogenic Vibrio parahaemolyticus strain. The LD50 for V. parahaemolyticus was 5.5 log CFU mL-1. The three probiotic strains, L. plantarum 69Cr with 104 CFU mL-1, L. fermentum 101Cc with 104 CFU mL-1, and L. casei 43Cg with 10³ CFU mL-1 conferred greater survival to the larvae than the control. The bacteria L. plantarum 69Cr and L. fermentum 101Cc conferred protection against the pathogen and significantly improved larval survival with an optimal dose of 104 CFU mL-1, whereas L. casei 43Cg did so with an optimal dose of 10³ CFU mL-1. The best survival percentage was achieved when the probiotic L. plantarum 69Cr was supplied. These results indicate that probiotic bacteria associated with, or originating from, Crassostrea gigas can protect their host from a pathogen such as V. parahaemolyticus. [ABSTRACT FROM AUTHOR]

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