COMPARISON OF THE GROWTH AND SURVIVAL OF LARVAL TURBOT IN THE ABSENCEOF CULTURABLE BACTERIA WITH THOSE IN THE PRESENCE OF VIBRIO-ANGUILLARUM, VIBRIO-ALGINOLYTICUS, OR A MARINE AEROMONAS SP

Larval turbot (Scophthalmus maximus) were reared on rotifers (Brachion us plicatilis) in the absence of culturable bacteria for up to 14 days and exhibited growth and high rates of survival (>55% in five experim ents). Low numbers of known bacteria were introduced into similar cult ures by exposure of the rotifers to a suspension of bacteria prior to addition of rotifers to the larval cultures; Vibrio anguillarum 91079 caused a highly significant decrease (P <0.01) in the proportion of su rvivors in two separate trials. With an Aeronomas sp. previously isola ted from a healthy batch of copepod-fed larvae, there was no significa nt difference in survival compared with control larvae, even though th e density of bacteria in the water of larval cultures reached 10(7) ml (-1). Bacteria colonized the gut of larvae exposed to Aeromonas-treate d rotifers to levels similar to those in conventionally reared fish (> 4 x 10(4) CFU per larva). Rearing of larvae in the presence of known b acteria provides a means of investigating the interaction of specific bacteria with turbot larvae and could provide a method for the selecti on of bacteria which may restrict the growth of opportunistic pathogen s which would be harmful to turbot larvae.