Dominant intestinal microflora of sea bream and sea bass larvae, from two hatcheries, during larval development

The intestinal microflora of larval sea bream (Dicentrarchus labrax) and sea bass (Sparus aurata) from two marine hatcheries (Greece and Spain) was studied, Samples for bacteriological analysis were taken during feeding regimes of the larvae with rotifers and Artemia. A total of five production cycles was examined: three involved sea bream and two involved sea bass, When the larvae were fed with rotifers, the incidence of Vibrio anguillarum, Vibrio tubiashii and non-vibrio groups was high. During feeding with Artemia, Vibrio alginolyticus, Vibrio proteolyticus, Vibrio harveyi and Vibrio natriegens were mainly isolated. During larval development, no dominant and persistent colonisation of the intestine by any given bacterial species was observed. Fluctuations in the composition of the dominant microflora appeared to reflect the bacterial composition of the ingested live feed. Selection towards the genus Vibrio was not observed until the larvae reached the end of the larval life stage. Two additional samples were taken during massive mortality outbreaks in bream larvae. In both samples, V. anguillarum was dominant as associated with the feeding with rotifers. The results suggest that disease outbreaks can occur when V. anguillarum dominates in the larval intestine. (C) 1997 Elsevier Science B.V.