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The accumulation of bacteria in Brachionus plicatilis and Artemia franciscana during a short-term incubation was quantified using immunocolony blot (ICB) and an enzyme-linked immunosorbent assay (ELISA). Four bacterial strains, isolated from turbot and halibut, were grazed effectively by both species when given at high concentrations (≥5×10 7 bacteria ml −1 ). B. plicatilis accumulated 21–63×10 3 bacteria per rotifer and A. franciscana up to 45×10 3 bacteria per metanauplius after 20–60 min of grazing. The composition of the bacterial microflora of the live food organisms changed drastically, as the bioencapsulated strains comprised up to 100% of the total count of colony-forming units. After incubation in the bacterial suspensions, B. plicatilis and A. franciscana were transferred to seawater with added microalgae ( Tetraselmis sp., 2 mg C l −1 ), to evaluate the persistence of the changed bacterial composition in conditions similar to those present in a first feeding tank. The bioencapsulated bacteria decreased in numbers, but in most cases remained present in both live food organisms after 24 h. It is possible, after a short-term incubation, to replace opportunistic (r-selected) bacteria present in the live food cultures with other bacteria, which persist as a dominant part of the bacterial flora of the live food for a relatively long period of time (4–24 h).

Two bacterial strains, 4:44 and PB52, isolated from turbot(Scophthalmus maximus L.) were used during a first feedingexperiment with turbot larvae. Bacteria were either added directly tothe water on the day of hatching of the larvae (day 0), orbioencapsulated in rotifers (Brachionus plicatilis) distributedon day 2 after hatching. The two bacterial strains were found to bepresent in the water of the rearing tanks throughout the experiment. Theaddition of bacteria influenced the species-composition of themicroflora associated with intensively produced rotifers added to thetanks, and resulted in colonization of the gut of the larvae by theadded bacterial strains. The strain 4:44 showed a peak on day 9 afterhatching, and reached a mean(sem) of 2.5(1.4) × 104bacteria per larva, when added in a mixture with PB52, and 0.4(0.1)× 104 bacteria per larva, when added alone. The strainPB52, on day 12 after hatching, reached 5.2(1.5) × 104bacteria per larva when added in a mixture with strain 4:44, and12.5(0.7) × 104 bacteria per larva, when added alone.The added bacteria colonized the gut turbot larvae, whereas thebacterial land, the survival and growth of the larvae were in most casesnot influenced in a negative way by the addition of bacteria.