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

Two bacterial strains, 4:44 and PB52, isolated from turbot (Scophthalmus ma ximus L.) were used during a first feeding experiment with turbot larvae. B acteria were either added directly to the water on the day of hatching of t he larvae (day 0), or bioencapsulated in rotifers (Brachionus plicatilis) d istributed on day 2 after hatching. The two bacterial strains were found to be present in the water of the rearing tanks throughout the experiment. Th e addition of bacteria influenced the species-composition of the microflora associated with intensively produced rotifers added to the tanks, and resu lted in colonization of the gut of the larvae by the added bacterial strain s. The strain 4:44 showed a peak on day 9 after hatching, and reached a mea n(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 strai n PB52, on day 12 after hatching, reached 5.2(1.5) x 10(4) bacteria per lar va 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 l arvae, whereas the bacterial land, the survival and growth of the larvae we re in most cases not influenced in a negative way by the addition of bacter ia.