| Summary: | Bacterial communities associated with fish larvae are highly influenced by the microbiota of live prey used as feed (rotifers or <i>Artemia</i>), generally dominated by bacterial strains with a low degree of specialization and high growth rates, (e.g., <i>Vibrionaceae</i>), which can be detrimental to larvae. Co-cultivation of microalgae used in the enrichment of <i>Artemia</i> (e.g., <i>Phaeodactylum tricornutum</i>, or <i>Chlorella minutissima</i>) with <i>Vibrio</i>-antagonistic probiotics belonging to the <i>Roseobacter</i> clade bacteria (e.g., <i>Phaeobacter</i> spp. or <i>Ruegeria</i> spp.) was studied. The introduction of the probiotics did not affect microalgae growth or significantly modify the composition of bacterial communities associated with both microalgae, as revealed by DGGE analysis. The inoculation of <i>P. tricornutum</i> with <i>Ruegeria</i> ALR6 allowed the maintenance of the probiotic in the scale-up of the microalgae cultures, both in axenic and non-axenic conditions. Using <i>Ruegeria</i>-inoculated <i>P. tricornutum</i> cultures in the enrichment of <i>Artemia</i> reduced the total <i>Vibrionaceae</i> count in <i>Artemia</i> by 2 Log units, therefore preventing the introduction of opportunistic or pathogenic bacteria to fish larvae fed with them.
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