To be considered probiotic, live organisms must be resistant to
bile salt, digestive enzymes, and the low pH of the stomach. Probiotics
associated with intestinal mucus can compete for adhesion
sites with pathogenic bacteria, produce bacteriocin, and release
other antimicrobial compounds in the mucus that enhance the
protective function of the mucous layer against pathogens [9e10].
Many pathogens of fish can cause damage to the intestinal epithelium
integrity [13e14]. Probiotics can reduce the number of potential
pathogens in the gastrointestinal tract and possibly reduce
the mucosal damage, leading to a lower maintenance expenditure
associated with the repair of injured tissues and thereby resulting in
improved organization and growth of these tissues.