The goals of this study were to determine the assembly sequence of phylotypes from a river into a bacterial biofilm as well as determining how the biofilm of putative fish probiotics influenced the natural assembly of a river biofilm. The putative probiotic strains had been isolated previously from sturgeon eggs and prior investigations indicated that some strains decreased egg mortality under hatchery conditions. By using probiotic strains early in hatchery protocols we hoped to alter the assembly of biofilm by preventing the establishment of pathogens within the biofilm and thereby reducing egg mortality. We successful showed that under laboratory conditions we could block the integration of known fish pathogens into biofilm by pretreating surfaces with specific strains and strain combinations.