The aerobic bacterial flora in the gut of turbot larvae and their influence on larval survival was examined. Two turbot experiments were run with six replicates each time. Large variation, from 0% up to 44%, was observed in the survival percentage of turbot larvae. There was no correlation between the number of bacteria present in the gut of turbot larvae and the larval survival rate. During both experiments, all replicates followed nearly the same rate of bacterial development in the gut of turbot larvae going from circa 10(2) CFU larva(-1) just before first feeding at day 3 post hatch to 10(5) CFU larva(-1) at day 9 post hatch.