The aquaculture industry must often deal in its cultures with bacterial contamination by Vibrio parahaemolyticus, which causes gastroenteritis in humans when they eat contaminated organisms. Until recently these pathogens were treated with antibiotics which are now forbidden because of their negative effects on humans and on the ecosystem. In the last few years there have been attempts to solve this problem by searching for active metabolites from antagonist bacteria. The objetive of this work was to evaluate the decrease of the load of the pathogen V. parahaemolyticus in Argopecten purpuratus scallops by the addition of oleic acid and diketopiperazines isolated from marine bacteria known for having an antibacterial effect against the pathogen, and with commercially available products similar to the molecular structures isolated from the bacteria. The decrease of the pathogen load was determined by the most probable number method from the absence in the samples of the gene tdh that codes for thermostable direct hemolysin (TDH), the main virulence factor in this species. The A. purpuratus bivalves treated with the oleic acid and diketopiperazines isolated from the bacteria showed preliminarily that they cause a reduction of the bacterial load of the V. parahaemolyticus pathogen. The same trend was seen when the scallops were treated with commercial oleic acid and diketopiperazines. Based on the inhibiting activity seen with the commercial products we suggest the possibility of experimenting with these products against V. parahaemolyticus or other pathogens in different commercially important organisms, mainly in depuration systems that require a short time (12 to 24 hours) to reduce the concentration of human pathogens like V. parahaemolyticus.