COMPARISON OF THE GUT BACTERIAL-FLORA OF START-FEEDING LARVAL TURBOT REARED UNDER DIFFERENT CONDITIONS

Bacterial colonization of the gut of turbot larvae coincided with the start of feeding and the gut microflora was then dominated by Vibrio a nd Aeromonas species. The detection of similar bacterial isolates over several days indicated the presence of a stable microflora during the rotifer feeding stage, probably reflecting a stable flora in the roti fer culture. There was no correlation between the number of bacteria i n the gut and larval survival rates; incidences of high mortalities we re not associated with high numbers of recognized fish pathogens, alth ough an Aeromonas species was implicated as an opportunistic pathogen. Potential pathogens were isolated, albeit in low numbers, from batche s of apparently healthy larvae with high survival rates. It is probabl e that the bacterial flora plays an important role in determining the survival of larval fish and that the establishment of a beneficial flo ra is possible, although the criteria for such a flora have still to b e elucidated.