Colonization of the gut in first feeding turbot by bacterial strains added to the water or bioencapsulated in rotifers

Two bacterial strains, 4:44 and PB52, isolated from turbot (Scophthalmus maximus L.) were used during a first feeding experiment with turbot larvae. Bacteria were either added directly to the water on the day of hatching of the larvae (day 0), or bioencapsulated in rotifers (Brachionus plicatilis) distributed on day 2 after hatching. The two bacterial strains were found to be present in the water of the rearing tanks throughout the experiment. The addition of bacteria influenced the species-composition of the microflora associated with intensively produced rotifers added to the tanks, and resulted in colonization of the gut of the larvae by the added bacterial strains. The strain 4:44 showed a peak on day 9 after hatching, and reached a mean(sem) of 2.5(1.4) x 10(4) bacteria per larva, when added in a mixture with PB52, and 0.4(0.1) x 10(4) bacteria per larva, when added alone. The strain PB52, on day 12 after hatching, reached 5.2(1.5) x 10(4) bacteria per larva when added in a mixture with strain 4:44, and 12.5(0.7) x 10(4) bacteria per larva, when added alone. The added bacteria colonized the gut turbot larvae, whereas the bacterial land, the survival and growth of the larvae were in most cases not influenced in a negative way by the addition of bacteria.