Aquaculture is one of the main sources of income in many countries worldwide. Intensive farms are often affected by different infectious diseases that can decrease their final production. To control this situation, several antibiotics are frequently used with known environmental consequences. The aim of this study was to analyze different bacterial
strains isolated from of gilthead sea bream, sea bass, sole and meagre guts, for use as
probiotics in aquaculture. The strains were evaluated in vitro through various
mechanisms of selection, such as the production of antagonistic effects against
pathogens, production of antibacterial substance, adhesion to the intestinal mucus,
competition for nutrients or binding site, and growth in intestinal mucus. A total of 50
bacterial strains were analyzed and only one showed excellent in vitro results for
consideration as a candidate to be analyzed in vivo. The strain, identified as Vagococcus
fluvialis, showed good protection against Vibrio anguillarum 975-1 in vivo in the
experimental challenge, showing a relative percent survival of 42.3% higher than positive
control group. Therefore, in conclusion we consider this strain to be a good candidate for
use as a future probiotic in aquaculture.