Bacterial antagonism is a common phenomenon in
nature; therefore, microbial interactions play a major
role in the equilibrium between competing beneficial
and potentially pathogenic microorganisms. However,
the composition of microbial communities can be
altered by husbandry practices and environmental
conditions that stimulate the proliferation of selected
bacterial species. It is well known that the microbiota
in the gastrointestinal tract of aquatic animals can be
modified, for example by ingestion of other micro-organisms; therefore, microbial manipulation consti-tutes a viable tool to reduce or eliminate the incidence
of opportunist pathogens