Bacteries associees aux production de Brachionus plicatilis

Bacteria associated with semi-continuous culture of Brachionus plicatilis , which is used as the first food of marine fish larvae, were counted on Zobell 2216 E medium and identified. The numbers of bacteria were very high in both Brachionus (about 10 super(11) bact. per ml of digestive content) and in water (from 1.6.10 super(6) to 4.7.10 super(7) bact. per ml). The cultures were studied at driving a time when mortalities occurred frequently. The introduction of a Pseudomonas) phenon at a proportion of about 50% to the dominant microflora persisted in time and was little influenced by diet. It has been the cause of the repression of the Vibrio, Aeromonas group which was found in an unusually small proportion. It induced a lack of microflora diversity and reduced its potentialities. The activity of this microflora would not be sufficient to allow the recycling of toxic metabolites which would accumulate or induce a deficiency of growth factors. The increase in the number of bacteria present in Brachionus at the time of the mortalities could be explained by the toxins blocking movement of these organisms.